source: trunk/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory.CSharp-5.5.0/Resolver/CSharpResolver.cs

// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
// 
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// software and associated documentation files (the "Software"), to deal in the Software
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// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
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using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using ICSharpCode.NRefactory.CSharp.TypeSystem;
using ICSharpCode.NRefactory.Semantics;
using ICSharpCode.NRefactory.TypeSystem;
using ICSharpCode.NRefactory.TypeSystem.Implementation;
using ICSharpCode.NRefactory.Utils;

namespace ICSharpCode.NRefactory.CSharp.Resolver
{
  /// <summary>
  /// Contains the main resolver logic.
  /// </summary>
  /// <remarks>
  /// This class is thread-safe.
  /// </remarks>
  public class CSharpResolver : ICodeContext
  {
    static readonly ResolveResult ErrorResult = ErrorResolveResult.UnknownError;
    readonly ICompilation compilation;
    internal readonly CSharpConversions conversions;
    readonly CSharpTypeResolveContext context;
    readonly bool checkForOverflow;
    readonly bool isWithinLambdaExpression;
    
    #region Constructor
    public CSharpResolver(ICompilation compilation)
    {
      if (compilation == null)
        throw new ArgumentNullException("compilation");
      this.compilation = compilation;
      this.conversions = CSharpConversions.Get(compilation);
      this.context = new CSharpTypeResolveContext(compilation.MainAssembly);
      
      var pc = compilation.MainAssembly.UnresolvedAssembly as CSharpProjectContent;
      if (pc != null) {
        this.checkForOverflow = pc.CompilerSettings.CheckForOverflow;
      }
    }
    
    public CSharpResolver(CSharpTypeResolveContext context)
    {
      if (context == null)
        throw new ArgumentNullException("context");
      this.compilation = context.Compilation;
      this.conversions = CSharpConversions.Get(compilation);
      this.context = context;
      if (context.CurrentTypeDefinition != null)
        currentTypeDefinitionCache = new TypeDefinitionCache(context.CurrentTypeDefinition);
    }
    
    private CSharpResolver(ICompilation compilation, CSharpConversions conversions, CSharpTypeResolveContext context, bool checkForOverflow, bool isWithinLambdaExpression, TypeDefinitionCache currentTypeDefinitionCache, ImmutableStack<IVariable> localVariableStack, ObjectInitializerContext objectInitializerStack)
    {
      this.compilation = compilation;
      this.conversions = conversions;
      this.context = context;
      this.checkForOverflow = checkForOverflow;
      this.isWithinLambdaExpression = isWithinLambdaExpression;
      this.currentTypeDefinitionCache = currentTypeDefinitionCache;
      this.localVariableStack = localVariableStack;
      this.objectInitializerStack = objectInitializerStack;
    }
    #endregion
    
    #region Properties
    /// <summary>
    /// Gets the compilation used by the resolver.
    /// </summary>
    public ICompilation Compilation {
      get { return compilation; }
    }
    
    /// <summary>
    /// Gets the current type resolve context.
    /// </summary>
    public CSharpTypeResolveContext CurrentTypeResolveContext {
      get { return context; }
    }

    IAssembly ITypeResolveContext.CurrentAssembly {
      get { return context.CurrentAssembly; }
    }
    
    CSharpResolver WithContext(CSharpTypeResolveContext newContext)
    {
      return new CSharpResolver(compilation, conversions, newContext, checkForOverflow, isWithinLambdaExpression, currentTypeDefinitionCache, localVariableStack, objectInitializerStack);
    }
    
    /// <summary>
    /// Gets whether the current context is <c>checked</c>.
    /// </summary>
    public bool CheckForOverflow {
      get { return checkForOverflow; }
    }
    
    /// <summary>
    /// Sets whether the current context is <c>checked</c>.
    /// </summary>
    public CSharpResolver WithCheckForOverflow(bool checkForOverflow)
    {
      if (checkForOverflow == this.checkForOverflow)
        return this;
      return new CSharpResolver(compilation, conversions, context, checkForOverflow, isWithinLambdaExpression, currentTypeDefinitionCache, localVariableStack, objectInitializerStack);
    }
    
    /// <summary>
    /// Gets whether the resolver is currently within a lambda expression or anonymous method.
    /// </summary>
    public bool IsWithinLambdaExpression {
      get { return isWithinLambdaExpression; }
    }
    
    /// <summary>
    /// Sets whether the resolver is currently within a lambda expression.
    /// </summary>
    public CSharpResolver WithIsWithinLambdaExpression(bool isWithinLambdaExpression)
    {
      return new CSharpResolver(compilation, conversions, context, checkForOverflow, isWithinLambdaExpression, currentTypeDefinitionCache, localVariableStack, objectInitializerStack);
    }
    
    /// <summary>
    /// Gets the current member definition that is used to look up identifiers as parameters
    /// or type parameters.
    /// </summary>
    public IMember CurrentMember {
      get { return context.CurrentMember; }
    }
    
    /// <summary>
    /// Sets the current member definition.
    /// </summary>
    /// <remarks>Don't forget to also set CurrentTypeDefinition when setting CurrentMember;
    /// setting one of the properties does not automatically set the other.</remarks>
    public CSharpResolver WithCurrentMember(IMember member)
    {
      return WithContext(context.WithCurrentMember(member));
    }
    
    ITypeResolveContext ITypeResolveContext.WithCurrentMember(IMember member)
    {
      return WithCurrentMember(member);
    }
    
    /// <summary>
    /// Gets the current using scope that is used to look up identifiers as class names.
    /// </summary>
    public ResolvedUsingScope CurrentUsingScope {
      get { return context.CurrentUsingScope; }
    }
    
    /// <summary>
    /// Sets the current using scope that is used to look up identifiers as class names.
    /// </summary>
    public CSharpResolver WithCurrentUsingScope(ResolvedUsingScope usingScope)
    {
      return WithContext(context.WithUsingScope(usingScope));
    }
    #endregion
    
    #region Per-CurrentTypeDefinition Cache
    readonly TypeDefinitionCache currentTypeDefinitionCache;
    
    /// <summary>
    /// Gets the current type definition.
    /// </summary>
    public ITypeDefinition CurrentTypeDefinition {
      get { return context.CurrentTypeDefinition; }
    }
    
    /// <summary>
    /// Sets the current type definition.
    /// </summary>
    public CSharpResolver WithCurrentTypeDefinition(ITypeDefinition typeDefinition)
    {
      if (this.CurrentTypeDefinition == typeDefinition)
        return this;
      
      TypeDefinitionCache newTypeDefinitionCache;
      if (typeDefinition != null)
        newTypeDefinitionCache = new TypeDefinitionCache(typeDefinition);
      else
        newTypeDefinitionCache = null;
      
      return new CSharpResolver(compilation, conversions, context.WithCurrentTypeDefinition(typeDefinition),
                                checkForOverflow, isWithinLambdaExpression, newTypeDefinitionCache, localVariableStack, objectInitializerStack);
    }
    
    ITypeResolveContext ITypeResolveContext.WithCurrentTypeDefinition(ITypeDefinition typeDefinition)
    {
      return WithCurrentTypeDefinition(typeDefinition);
    }
    
    sealed class TypeDefinitionCache
    {
      public readonly ITypeDefinition TypeDefinition;
      public readonly Dictionary<string, ResolveResult> SimpleNameLookupCacheExpression = new Dictionary<string, ResolveResult>();
      public readonly Dictionary<string, ResolveResult> SimpleNameLookupCacheInvocationTarget = new Dictionary<string, ResolveResult>();
      public readonly Dictionary<string, ResolveResult> SimpleTypeLookupCache = new Dictionary<string, ResolveResult>();
      
      public TypeDefinitionCache(ITypeDefinition typeDefinition)
      {
        this.TypeDefinition = typeDefinition;
      }
    }
    #endregion
    
    #region Local Variable Management
    
    // We store the local variables in an immutable stack.
    // The beginning of a block is marked by a null entry.
    
    // This data structure is used to allow efficient cloning of the resolver with its local variable context.
    readonly ImmutableStack<IVariable> localVariableStack = ImmutableStack<IVariable>.Empty;
    
    CSharpResolver WithLocalVariableStack(ImmutableStack<IVariable> stack)
    {
      return new CSharpResolver(compilation, conversions, context, checkForOverflow, isWithinLambdaExpression, currentTypeDefinitionCache, stack, objectInitializerStack);
    }
    
    /// <summary>
    /// Opens a new scope for local variables.
    /// </summary>
    public CSharpResolver PushBlock()
    {
      return WithLocalVariableStack(localVariableStack.Push(null));
    }
    
    /// <summary>
    /// Closes the current scope for local variables; removing all variables in that scope.
    /// </summary>
    public CSharpResolver PopBlock()
    {
      var stack = localVariableStack;
      IVariable removedVar;
      do {
        removedVar = stack.Peek();
        stack = stack.Pop();
      } while (removedVar != null);
      return WithLocalVariableStack(stack);
    }
    
    /// <summary>
    /// Adds a new variable or lambda parameter to the current block.
    /// </summary>
    public CSharpResolver AddVariable(IVariable variable)
    {
      if (variable == null)
        throw new ArgumentNullException("variable");
      return WithLocalVariableStack(localVariableStack.Push(variable));
    }
    
    /// <summary>
    /// Removes the variable that was just added.
    /// </summary>
    public CSharpResolver PopLastVariable()
    {
      if (localVariableStack.Peek() == null)
        throw new InvalidOperationException("There is no variable within the current block.");
      return WithLocalVariableStack(localVariableStack.Pop());
    }
    
    /// <summary>
    /// Gets all currently visible local variables and lambda parameters.
    /// Does not include method parameters.
    /// </summary>
    public IEnumerable<IVariable> LocalVariables {
      get {
        return localVariableStack.Where(v => v != null);
      }
    }
    #endregion
    
    #region Object Initializer Context
    sealed class ObjectInitializerContext
    {
      internal readonly ResolveResult initializedObject;
      internal readonly ObjectInitializerContext prev;
      
      public ObjectInitializerContext(ResolveResult initializedObject, CSharpResolver.ObjectInitializerContext prev)
      {
        this.initializedObject = initializedObject;
        this.prev = prev;
      }
    }
    
    readonly ObjectInitializerContext objectInitializerStack;
    
    CSharpResolver WithObjectInitializerStack(ObjectInitializerContext stack)
    {
      return new CSharpResolver(compilation, conversions, context, checkForOverflow, isWithinLambdaExpression, currentTypeDefinitionCache, localVariableStack, stack);
    }
    
    /// <summary>
    /// Pushes the type of the object that is currently being initialized.
    /// </summary>
    public CSharpResolver PushObjectInitializer(ResolveResult initializedObject)
    {
      if (initializedObject == null)
        throw new ArgumentNullException("initializedObject");
      return WithObjectInitializerStack(new ObjectInitializerContext(initializedObject, objectInitializerStack));
    }
    
    public CSharpResolver PopObjectInitializer()
    {
      if (objectInitializerStack == null)
        throw new InvalidOperationException();
      return WithObjectInitializerStack(objectInitializerStack.prev);
    }
    
    /// <summary>
    /// Gets whether this context is within an object initializer.
    /// </summary>
    public bool IsInObjectInitializer {
      get { return objectInitializerStack != null; }
    }
    
    /// <summary>
    /// Gets the current object initializer. This usually is an <see cref="InitializedObjectResolveResult"/>
    /// or (for nested initializers) a semantic tree based on an <see cref="InitializedObjectResolveResult"/>.
    /// Returns ErrorResolveResult if there is no object initializer.
    /// </summary>
    public ResolveResult CurrentObjectInitializer {
      get {
        return objectInitializerStack != null ? objectInitializerStack.initializedObject : ErrorResult;
      }
    }
    
    /// <summary>
    /// Gets the type of the object currently being initialized.
    /// Returns SharedTypes.Unknown if no object initializer is currently open (or if the object initializer
    /// has unknown type).
    /// </summary>
    public IType CurrentObjectInitializerType {
      get { return CurrentObjectInitializer.Type; }
    }
    #endregion
    
    #region Clone
    /// <summary>
    /// Creates a copy of this CSharp resolver.
    /// </summary>
    [Obsolete("CSharpResolver is immutable, cloning is no longer necessary")]
    public CSharpResolver Clone()
    {
      return this;
    }
    #endregion
    
    #region ResolveUnaryOperator
    #region ResolveUnaryOperator method
    public ResolveResult ResolveUnaryOperator(UnaryOperatorType op, ResolveResult expression)
    {
      if (expression.Type.Kind == TypeKind.Dynamic) {
        if (op == UnaryOperatorType.Await) {
          return new AwaitResolveResult(SpecialType.Dynamic, new DynamicInvocationResolveResult(new DynamicMemberResolveResult(expression, "GetAwaiter"), DynamicInvocationType.Invocation, EmptyList<ResolveResult>.Instance), SpecialType.Dynamic, null, null, null);
        }
        else {
          return UnaryOperatorResolveResult(SpecialType.Dynamic, op, expression);
        }
      }
      
      // C# 4.0 spec: §7.3.3 Unary operator overload resolution
      string overloadableOperatorName = GetOverloadableOperatorName(op);
      if (overloadableOperatorName == null) {
        switch (op) {
          case UnaryOperatorType.Dereference:
            PointerType p = expression.Type as PointerType;
            if (p != null)
              return UnaryOperatorResolveResult(p.ElementType, op, expression);
            else
              return ErrorResult;
          case UnaryOperatorType.AddressOf:
            return UnaryOperatorResolveResult(new PointerType(expression.Type), op, expression);
          case UnaryOperatorType.Await: {
            ResolveResult getAwaiterMethodGroup = ResolveMemberAccess(expression, "GetAwaiter", EmptyList<IType>.Instance, NameLookupMode.InvocationTarget);
            ResolveResult getAwaiterInvocation = ResolveInvocation(getAwaiterMethodGroup, new ResolveResult[0], argumentNames: null, allowOptionalParameters: false);

            var lookup = CreateMemberLookup();
            IMethod getResultMethod;
            IType awaitResultType;
            var getResultMethodGroup = lookup.Lookup(getAwaiterInvocation, "GetResult", EmptyList<IType>.Instance, true) as MethodGroupResolveResult;
            if (getResultMethodGroup != null) {
              var getResultOR = getResultMethodGroup.PerformOverloadResolution(compilation, new ResolveResult[0], allowExtensionMethods: false, conversions: conversions);
              getResultMethod = getResultOR.FoundApplicableCandidate ? getResultOR.GetBestCandidateWithSubstitutedTypeArguments() as IMethod : null;
              awaitResultType = getResultMethod != null ? getResultMethod.ReturnType : SpecialType.UnknownType;
            }
            else {
              getResultMethod = null;
              awaitResultType = SpecialType.UnknownType;
            }

            var isCompletedRR = lookup.Lookup(getAwaiterInvocation, "IsCompleted", EmptyList<IType>.Instance, false);
            var isCompletedProperty = (isCompletedRR is MemberResolveResult ? ((MemberResolveResult)isCompletedRR).Member as IProperty : null);
            if (isCompletedProperty != null && (!isCompletedProperty.ReturnType.IsKnownType(KnownTypeCode.Boolean) || !isCompletedProperty.CanGet))
              isCompletedProperty = null;

            var interfaceOnCompleted = compilation.FindType(KnownTypeCode.INotifyCompletion).GetMethods().FirstOrDefault(x => x.Name == "OnCompleted");
            var interfaceUnsafeOnCompleted = compilation.FindType(KnownTypeCode.ICriticalNotifyCompletion).GetMethods().FirstOrDefault(x => x.Name == "UnsafeOnCompleted");

            IMethod onCompletedMethod = null;
            var candidates = getAwaiterInvocation.Type.GetMethods().Where(x => x.ImplementedInterfaceMembers.Select(y => y.MemberDefinition).Contains(interfaceUnsafeOnCompleted)).ToList();
            if (candidates.Count == 0) {
              candidates = getAwaiterInvocation.Type.GetMethods().Where(x => x.ImplementedInterfaceMembers.Select(y => y.MemberDefinition).Contains(interfaceOnCompleted)).ToList();
              if (candidates.Count == 1)
                onCompletedMethod = candidates[0];
            }
            else if (candidates.Count == 1) {
              onCompletedMethod = candidates[0];
            }

            return new AwaitResolveResult(awaitResultType, getAwaiterInvocation, getAwaiterInvocation.Type, isCompletedProperty, onCompletedMethod, getResultMethod);
          }

          default:
            return ErrorResolveResult.UnknownError;
        }
      }
      // If the type is nullable, get the underlying type:
      IType type = NullableType.GetUnderlyingType(expression.Type);
      bool isNullable = NullableType.IsNullable(expression.Type);
      
      // the operator is overloadable:
      OverloadResolution userDefinedOperatorOR = CreateOverloadResolution(new[] { expression });
      foreach (var candidate in GetUserDefinedOperatorCandidates(type, overloadableOperatorName)) {
        userDefinedOperatorOR.AddCandidate(candidate);
      }
      if (userDefinedOperatorOR.FoundApplicableCandidate) {
        return CreateResolveResultForUserDefinedOperator(userDefinedOperatorOR, UnaryOperatorExpression.GetLinqNodeType(op, this.CheckForOverflow));
      }
      
      expression = UnaryNumericPromotion(op, ref type, isNullable, expression);
      CSharpOperators.OperatorMethod[] methodGroup;
      CSharpOperators operators = CSharpOperators.Get(compilation);
      switch (op) {
        case UnaryOperatorType.Increment:
        case UnaryOperatorType.Decrement:
        case UnaryOperatorType.PostIncrement:
        case UnaryOperatorType.PostDecrement:
          // C# 4.0 spec: §7.6.9 Postfix increment and decrement operators
          // C# 4.0 spec: §7.7.5 Prefix increment and decrement operators
          TypeCode code = ReflectionHelper.GetTypeCode(type);
          if ((code >= TypeCode.Char && code <= TypeCode.Decimal) || type.Kind == TypeKind.Enum || type.Kind == TypeKind.Pointer)
            return UnaryOperatorResolveResult(expression.Type, op, expression, isNullable);
          else
            return new ErrorResolveResult(expression.Type);
        case UnaryOperatorType.Plus:
          methodGroup = operators.UnaryPlusOperators;
          break;
        case UnaryOperatorType.Minus:
          methodGroup = CheckForOverflow ? operators.CheckedUnaryMinusOperators : operators.UncheckedUnaryMinusOperators;
          break;
        case UnaryOperatorType.Not:
          methodGroup = operators.LogicalNegationOperators;
          break;
        case UnaryOperatorType.BitNot:
          if (type.Kind == TypeKind.Enum) {
            if (expression.IsCompileTimeConstant && !isNullable && expression.ConstantValue != null) {
              // evaluate as (E)(~(U)x);
              var U = compilation.FindType(expression.ConstantValue.GetType());
              var unpackedEnum = new ConstantResolveResult(U, expression.ConstantValue);
              var rr = ResolveUnaryOperator(op, unpackedEnum);
              rr = WithCheckForOverflow(false).ResolveCast(type, rr);
              if (rr.IsCompileTimeConstant)
                return rr;
            } 
            return UnaryOperatorResolveResult(expression.Type, op, expression, isNullable);
          } else {
            methodGroup = operators.BitwiseComplementOperators;
            break;
          }
        default:
          throw new InvalidOperationException();
      }
      OverloadResolution builtinOperatorOR = CreateOverloadResolution(new[] { expression });
      foreach (var candidate in methodGroup) {
        builtinOperatorOR.AddCandidate(candidate);
      }
      CSharpOperators.UnaryOperatorMethod m = (CSharpOperators.UnaryOperatorMethod)builtinOperatorOR.BestCandidate;
      IType resultType = m.ReturnType;
      if (builtinOperatorOR.BestCandidateErrors != OverloadResolutionErrors.None) {
        if (userDefinedOperatorOR.BestCandidate != null) {
          // If there are any user-defined operators, prefer those over the built-in operators.
          // It'll be a more informative error.
          return CreateResolveResultForUserDefinedOperator(userDefinedOperatorOR, UnaryOperatorExpression.GetLinqNodeType(op, this.CheckForOverflow));
        } else if (builtinOperatorOR.BestCandidateAmbiguousWith != null) {
          // If the best candidate is ambiguous, just use the input type instead
          // of picking one of the ambiguous overloads.
          return new ErrorResolveResult(expression.Type);
        } else {
          return new ErrorResolveResult(resultType);
        }
      } else if (expression.IsCompileTimeConstant && m.CanEvaluateAtCompileTime) {
        object val;
        try {
          val = m.Invoke(this, expression.ConstantValue);
        } catch (ArithmeticException) {
          return new ErrorResolveResult(resultType);
        }
        return new ConstantResolveResult(resultType, val);
      } else {
        expression = Convert(expression, m.Parameters[0].Type, builtinOperatorOR.ArgumentConversions[0]);
        return UnaryOperatorResolveResult(resultType, op, expression,
                                          builtinOperatorOR.BestCandidate is OverloadResolution.ILiftedOperator);
      }
    }
    
    OperatorResolveResult UnaryOperatorResolveResult(IType resultType, UnaryOperatorType op, ResolveResult expression, bool isLifted = false)
    {
      return new OperatorResolveResult(
        resultType, UnaryOperatorExpression.GetLinqNodeType(op, this.CheckForOverflow),
        null, isLifted, new[] { expression });
    }
    #endregion
    
    #region UnaryNumericPromotion
    ResolveResult UnaryNumericPromotion(UnaryOperatorType op, ref IType type, bool isNullable, ResolveResult expression)
    {
      // C# 4.0 spec: §7.3.6.1
      TypeCode code = ReflectionHelper.GetTypeCode(type);
      if (isNullable && type.Kind == TypeKind.Null)
        code = TypeCode.SByte; // cause promotion of null to int32
      switch (op) {
        case UnaryOperatorType.Minus:
          if (code == TypeCode.UInt32) {
            type = compilation.FindType(KnownTypeCode.Int64);
            return Convert(expression, MakeNullable(type, isNullable),
                           isNullable ? Conversion.ImplicitNullableConversion : Conversion.ImplicitNumericConversion);
          }
          goto case UnaryOperatorType.Plus;
        case UnaryOperatorType.Plus:
        case UnaryOperatorType.BitNot:
          if (code >= TypeCode.Char && code <= TypeCode.UInt16) {
            type = compilation.FindType(KnownTypeCode.Int32);
            return Convert(expression, MakeNullable(type, isNullable),
                           isNullable ? Conversion.ImplicitNullableConversion : Conversion.ImplicitNumericConversion);
          }
          break;
      }
      return expression;
    }
    #endregion
    
    #region GetOverloadableOperatorName
    static string GetOverloadableOperatorName(UnaryOperatorType op)
    {
      switch (op) {
        case UnaryOperatorType.Not:
          return "op_LogicalNot";
        case UnaryOperatorType.BitNot:
          return "op_OnesComplement";
        case UnaryOperatorType.Minus:
          return "op_UnaryNegation";
        case UnaryOperatorType.Plus:
          return "op_UnaryPlus";
        case UnaryOperatorType.Increment:
        case UnaryOperatorType.PostIncrement:
          return "op_Increment";
        case UnaryOperatorType.Decrement:
        case UnaryOperatorType.PostDecrement:
          return "op_Decrement";
        default:
          return null;
      }
    }
    #endregion
    #endregion
    
    #region ResolveBinaryOperator
    #region ResolveBinaryOperator method
    public ResolveResult ResolveBinaryOperator(BinaryOperatorType op, ResolveResult lhs, ResolveResult rhs)
    {
      if (lhs.Type.Kind == TypeKind.Dynamic || rhs.Type.Kind == TypeKind.Dynamic) {
        lhs = Convert(lhs, SpecialType.Dynamic);
        rhs = Convert(rhs, SpecialType.Dynamic);
        return BinaryOperatorResolveResult(SpecialType.Dynamic, lhs, op, rhs);
      }
      
      // C# 4.0 spec: §7.3.4 Binary operator overload resolution
      string overloadableOperatorName = GetOverloadableOperatorName(op);
      if (overloadableOperatorName == null) {
        
        // Handle logical and/or exactly as bitwise and/or:
        // - If the user overloads a bitwise operator, that implicitly creates the corresponding logical operator.
        // - If both inputs are compile-time constants, it doesn't matter that we don't short-circuit.
        // - If inputs aren't compile-time constants, we don't evaluate anything, so again it doesn't matter that we don't short-circuit
        if (op == BinaryOperatorType.ConditionalAnd) {
          overloadableOperatorName = GetOverloadableOperatorName(BinaryOperatorType.BitwiseAnd);
        } else if (op == BinaryOperatorType.ConditionalOr) {
          overloadableOperatorName = GetOverloadableOperatorName(BinaryOperatorType.BitwiseOr);
        } else if (op == BinaryOperatorType.NullCoalescing) {
          // null coalescing operator is not overloadable and needs to be handled separately
          return ResolveNullCoalescingOperator(lhs, rhs);
        } else {
          return ErrorResolveResult.UnknownError;
        }
      }
      
      // If the type is nullable, get the underlying type:
      bool isNullable = NullableType.IsNullable(lhs.Type) || NullableType.IsNullable(rhs.Type);
      IType lhsType = NullableType.GetUnderlyingType(lhs.Type);
      IType rhsType = NullableType.GetUnderlyingType(rhs.Type);
      
      // the operator is overloadable:
      OverloadResolution userDefinedOperatorOR = CreateOverloadResolution(new[] { lhs, rhs });
      HashSet<IParameterizedMember> userOperatorCandidates = new HashSet<IParameterizedMember>();
      userOperatorCandidates.UnionWith(GetUserDefinedOperatorCandidates(lhsType, overloadableOperatorName));
      userOperatorCandidates.UnionWith(GetUserDefinedOperatorCandidates(rhsType, overloadableOperatorName));
      foreach (var candidate in userOperatorCandidates) {
        userDefinedOperatorOR.AddCandidate(candidate);
      }
      if (userDefinedOperatorOR.FoundApplicableCandidate) {
        return CreateResolveResultForUserDefinedOperator(userDefinedOperatorOR, BinaryOperatorExpression.GetLinqNodeType(op, this.CheckForOverflow));
      }
      
      if (lhsType.Kind == TypeKind.Null && rhsType.IsReferenceType == false
          || lhsType.IsReferenceType == false && rhsType.Kind == TypeKind.Null)
      {
        isNullable = true;
      }
      if (op == BinaryOperatorType.ShiftLeft || op == BinaryOperatorType.ShiftRight) {
        // special case: the shift operators allow "var x = null << null", producing int?.
        if (lhsType.Kind == TypeKind.Null && rhsType.Kind == TypeKind.Null)
          isNullable = true;
        // for shift operators, do unary promotion independently on both arguments
        lhs = UnaryNumericPromotion(UnaryOperatorType.Plus, ref lhsType, isNullable, lhs);
        rhs = UnaryNumericPromotion(UnaryOperatorType.Plus, ref rhsType, isNullable, rhs);
      } else {
        bool allowNullableConstants = op == BinaryOperatorType.Equality || op == BinaryOperatorType.InEquality;
        if (!BinaryNumericPromotion(isNullable, ref lhs, ref rhs, allowNullableConstants))
          return new ErrorResolveResult(lhs.Type);
      }
      // re-read underlying types after numeric promotion
      lhsType = NullableType.GetUnderlyingType(lhs.Type);
      rhsType = NullableType.GetUnderlyingType(rhs.Type);
      
      IEnumerable<CSharpOperators.OperatorMethod> methodGroup;
      CSharpOperators operators = CSharpOperators.Get(compilation);
      switch (op) {
        case BinaryOperatorType.Multiply:
          methodGroup = operators.MultiplicationOperators;
          break;
        case BinaryOperatorType.Divide:
          methodGroup = operators.DivisionOperators;
          break;
        case BinaryOperatorType.Modulus:
          methodGroup = operators.RemainderOperators;
          break;
        case BinaryOperatorType.Add:
          methodGroup = operators.AdditionOperators;
          {
            if (lhsType.Kind == TypeKind.Enum) {
              // E operator +(E x, U y);
              IType underlyingType = MakeNullable(GetEnumUnderlyingType(lhsType), isNullable);
              if (TryConvertEnum(ref rhs, underlyingType, ref isNullable, ref lhs)) {
                return HandleEnumOperator(isNullable, lhsType, op, lhs, rhs);
              }
            }
            if (rhsType.Kind == TypeKind.Enum) {
              // E operator +(U x, E y);
              IType underlyingType = MakeNullable(GetEnumUnderlyingType(rhsType), isNullable);
              if (TryConvertEnum(ref lhs, underlyingType, ref isNullable, ref rhs)) {
                return HandleEnumOperator(isNullable, rhsType, op, lhs, rhs);
              }
            }
            
            if (lhsType.Kind == TypeKind.Delegate && TryConvert(ref rhs, lhsType)) {
              return BinaryOperatorResolveResult(lhsType, lhs, op, rhs);
            } else if (rhsType.Kind == TypeKind.Delegate && TryConvert(ref lhs, rhsType)) {
              return BinaryOperatorResolveResult(rhsType, lhs, op, rhs);
            }
            
            if (lhsType is PointerType) {
              methodGroup = new [] {
                PointerArithmeticOperator(lhsType, lhsType, KnownTypeCode.Int32),
                PointerArithmeticOperator(lhsType, lhsType, KnownTypeCode.UInt32),
                PointerArithmeticOperator(lhsType, lhsType, KnownTypeCode.Int64),
                PointerArithmeticOperator(lhsType, lhsType, KnownTypeCode.UInt64)
              };
            } else if (rhsType is PointerType) {
              methodGroup = new [] {
                PointerArithmeticOperator(rhsType, KnownTypeCode.Int32, rhsType),
                PointerArithmeticOperator(rhsType, KnownTypeCode.UInt32, rhsType),
                PointerArithmeticOperator(rhsType, KnownTypeCode.Int64, rhsType),
                PointerArithmeticOperator(rhsType, KnownTypeCode.UInt64, rhsType)
              };
            }
            if (lhsType.Kind == TypeKind.Null && rhsType.Kind == TypeKind.Null)
              return new ErrorResolveResult(SpecialType.NullType);
          }
          break;
        case BinaryOperatorType.Subtract:
          methodGroup = operators.SubtractionOperators;
          {
            if (lhsType.Kind == TypeKind.Enum) {
              // U operator –(E x, E y);
              if (TryConvertEnum(ref rhs, lhs.Type, ref isNullable, ref lhs, allowConversionFromConstantZero: false)) {
                return HandleEnumSubtraction(isNullable, lhsType, lhs, rhs);
              }

              // E operator –(E x, U y);
              IType underlyingType = MakeNullable(GetEnumUnderlyingType(lhsType), isNullable);
              if (TryConvertEnum(ref rhs, underlyingType, ref isNullable, ref lhs)) {
                return HandleEnumOperator(isNullable, lhsType, op, lhs, rhs);
              }
            }
            if (rhsType.Kind == TypeKind.Enum) {
              // U operator –(E x, E y);
              if (TryConvertEnum(ref lhs, rhs.Type, ref isNullable, ref rhs, allowConversionFromConstantZero: false)) {
                return HandleEnumSubtraction(isNullable, rhsType, lhs, rhs);
              }

              // E operator -(U x, E y);
              IType underlyingType = MakeNullable(GetEnumUnderlyingType(rhsType), isNullable);
              if (TryConvertEnum(ref lhs, underlyingType, ref isNullable, ref rhs)) {
                return HandleEnumOperator(isNullable, rhsType, op, lhs, rhs);
              }
            }
            
            if (lhsType.Kind == TypeKind.Delegate && TryConvert(ref rhs, lhsType)) {
              return BinaryOperatorResolveResult(lhsType, lhs, op, rhs);
            } else if (rhsType.Kind == TypeKind.Delegate && TryConvert(ref lhs, rhsType)) {
              return BinaryOperatorResolveResult(rhsType, lhs, op, rhs);
            }
            
            if (lhsType is PointerType) {
              if (rhsType is PointerType) {
                IType int64 = compilation.FindType(KnownTypeCode.Int64);
                if (lhsType.Equals(rhsType)) {
                  return BinaryOperatorResolveResult(int64, lhs, op, rhs);
                } else {
                  return new ErrorResolveResult(int64);
                }
              }
              methodGroup = new [] {
                PointerArithmeticOperator(lhsType, lhsType, KnownTypeCode.Int32),
                PointerArithmeticOperator(lhsType, lhsType, KnownTypeCode.UInt32),
                PointerArithmeticOperator(lhsType, lhsType, KnownTypeCode.Int64),
                PointerArithmeticOperator(lhsType, lhsType, KnownTypeCode.UInt64)
              };
            }
            
            if (lhsType.Kind == TypeKind.Null && rhsType.Kind == TypeKind.Null)
              return new ErrorResolveResult(SpecialType.NullType);
          }
          break;
        case BinaryOperatorType.ShiftLeft:
          methodGroup = operators.ShiftLeftOperators;
          break;
        case BinaryOperatorType.ShiftRight:
          methodGroup = operators.ShiftRightOperators;
          break;
        case BinaryOperatorType.Equality:
        case BinaryOperatorType.InEquality:
        case BinaryOperatorType.LessThan:
        case BinaryOperatorType.GreaterThan:
        case BinaryOperatorType.LessThanOrEqual:
        case BinaryOperatorType.GreaterThanOrEqual:
          {
            if (lhsType.Kind == TypeKind.Enum && TryConvert(ref rhs, lhs.Type)) {
              // bool operator op(E x, E y);
              return HandleEnumComparison(op, lhsType, isNullable, lhs, rhs);
            } else if (rhsType.Kind == TypeKind.Enum && TryConvert(ref lhs, rhs.Type)) {
              // bool operator op(E x, E y);
              return HandleEnumComparison(op, rhsType, isNullable, lhs, rhs);
            } else if (lhsType is PointerType && rhsType is PointerType) {
              return BinaryOperatorResolveResult(compilation.FindType(KnownTypeCode.Boolean), lhs, op, rhs);
            }
            if (op == BinaryOperatorType.Equality || op == BinaryOperatorType.InEquality) {
              if (lhsType.IsReferenceType == true && rhsType.IsReferenceType == true) {
                // If it's a reference comparison
                if (op == BinaryOperatorType.Equality)
                  methodGroup = operators.ReferenceEqualityOperators;
                else
                  methodGroup = operators.ReferenceInequalityOperators;
                break;
              } else if (lhsType.Kind == TypeKind.Null && IsNullableTypeOrNonValueType(rhs.Type)
                         || IsNullableTypeOrNonValueType(lhs.Type) && rhsType.Kind == TypeKind.Null) {
                // compare type parameter or nullable type with the null literal
                return BinaryOperatorResolveResult(compilation.FindType(KnownTypeCode.Boolean), lhs, op, rhs);
              }
            }
            switch (op) {
              case BinaryOperatorType.Equality:
                methodGroup = operators.ValueEqualityOperators;
                break;
              case BinaryOperatorType.InEquality:
                methodGroup = operators.ValueInequalityOperators;
                break;
              case BinaryOperatorType.LessThan:
                methodGroup = operators.LessThanOperators;
                break;
              case BinaryOperatorType.GreaterThan:
                methodGroup = operators.GreaterThanOperators;
                break;
              case BinaryOperatorType.LessThanOrEqual:
                methodGroup = operators.LessThanOrEqualOperators;
                break;
              case BinaryOperatorType.GreaterThanOrEqual:
                methodGroup = operators.GreaterThanOrEqualOperators;
                break;
              default:
                throw new InvalidOperationException();
            }
          }
          break;
        case BinaryOperatorType.BitwiseAnd:
        case BinaryOperatorType.BitwiseOr:
        case BinaryOperatorType.ExclusiveOr:
          {
            if (lhsType.Kind == TypeKind.Enum) {
              // bool operator op(E x, E y);
              if (TryConvertEnum(ref rhs, lhs.Type, ref isNullable, ref lhs)) {
                return HandleEnumOperator(isNullable, lhsType, op, lhs, rhs);
              }
            }

            if (rhsType.Kind == TypeKind.Enum) {
              // bool operator op(E x, E y);
              if (TryConvertEnum (ref lhs, rhs.Type, ref isNullable, ref rhs)) {
                return HandleEnumOperator(isNullable, rhsType, op, lhs, rhs);
              }
            }
            
            switch (op) {
              case BinaryOperatorType.BitwiseAnd:
                methodGroup = operators.BitwiseAndOperators;
                break;
              case BinaryOperatorType.BitwiseOr:
                methodGroup = operators.BitwiseOrOperators;
                break;
              case BinaryOperatorType.ExclusiveOr:
                methodGroup = operators.BitwiseXorOperators;
                break;
              default:
                throw new InvalidOperationException();
            }
          }
          break;
        case BinaryOperatorType.ConditionalAnd:
          methodGroup = operators.LogicalAndOperators;
          break;
        case BinaryOperatorType.ConditionalOr:
          methodGroup = operators.LogicalOrOperators;
          break;
        default:
          throw new InvalidOperationException();
      }
      OverloadResolution builtinOperatorOR = CreateOverloadResolution(new[] { lhs, rhs });
      foreach (var candidate in methodGroup) {
        builtinOperatorOR.AddCandidate(candidate);
      }
      CSharpOperators.BinaryOperatorMethod m = (CSharpOperators.BinaryOperatorMethod)builtinOperatorOR.BestCandidate;
      IType resultType = m.ReturnType;
      if (builtinOperatorOR.BestCandidateErrors != OverloadResolutionErrors.None) {
        // If there are any user-defined operators, prefer those over the built-in operators.
        // It'll be a more informative error.
        if (userDefinedOperatorOR.BestCandidate != null)
          return CreateResolveResultForUserDefinedOperator(userDefinedOperatorOR, BinaryOperatorExpression.GetLinqNodeType(op, this.CheckForOverflow));
        else
          return new ErrorResolveResult(resultType);
      } else if (lhs.IsCompileTimeConstant && rhs.IsCompileTimeConstant && m.CanEvaluateAtCompileTime) {
        object val;
        try {
          val = m.Invoke(this, lhs.ConstantValue, rhs.ConstantValue);
        } catch (ArithmeticException) {
          return new ErrorResolveResult(resultType);
        }
        return new ConstantResolveResult(resultType, val);
      } else {
        lhs = Convert(lhs, m.Parameters[0].Type, builtinOperatorOR.ArgumentConversions[0]);
        rhs = Convert(rhs, m.Parameters[1].Type, builtinOperatorOR.ArgumentConversions[1]);
        return BinaryOperatorResolveResult(resultType, lhs, op, rhs,
                                           builtinOperatorOR.BestCandidate is OverloadResolution.ILiftedOperator);
      }
    }
    
    bool IsNullableTypeOrNonValueType(IType type)
    {
      return NullableType.IsNullable(type) || type.IsReferenceType != false;
    }
    
    ResolveResult BinaryOperatorResolveResult(IType resultType, ResolveResult lhs, BinaryOperatorType op, ResolveResult rhs, bool isLifted = false)
    {
      return new OperatorResolveResult(
        resultType, BinaryOperatorExpression.GetLinqNodeType(op, this.CheckForOverflow),
        null, isLifted, new[] { lhs, rhs });
    }
    #endregion
    
    #region Pointer arithmetic
    CSharpOperators.BinaryOperatorMethod PointerArithmeticOperator(IType resultType, IType inputType1, KnownTypeCode inputType2)
    {
      return PointerArithmeticOperator(resultType, inputType1, compilation.FindType(inputType2));
    }
    
    CSharpOperators.BinaryOperatorMethod PointerArithmeticOperator(IType resultType, KnownTypeCode inputType1, IType inputType2)
    {
      return PointerArithmeticOperator(resultType, compilation.FindType(inputType1), inputType2);
    }
    
    CSharpOperators.BinaryOperatorMethod PointerArithmeticOperator(IType resultType, IType inputType1, IType inputType2)
    {
      return new CSharpOperators.BinaryOperatorMethod(compilation) {
        ReturnType = resultType,
        Parameters = {
          new DefaultParameter(inputType1, string.Empty),
          new DefaultParameter(inputType2, string.Empty)
        }
      };
    }
    #endregion
    
    #region Enum helper methods
    IType GetEnumUnderlyingType(IType enumType)
    {
      ITypeDefinition def = enumType.GetDefinition();
      return def != null ? def.EnumUnderlyingType : SpecialType.UnknownType;
    }
    
    /// <summary>
    /// Handle the case where an enum value is compared with another enum value
    /// bool operator op(E x, E y);
    /// </summary>
    ResolveResult HandleEnumComparison(BinaryOperatorType op, IType enumType, bool isNullable, ResolveResult lhs, ResolveResult rhs)
    {
      // evaluate as ((U)x op (U)y)
      IType elementType = GetEnumUnderlyingType(enumType);
      if (lhs.IsCompileTimeConstant && rhs.IsCompileTimeConstant && !isNullable && elementType.Kind != TypeKind.Enum) {
        var rr = ResolveBinaryOperator(op, ResolveCast(elementType, lhs), ResolveCast(elementType, rhs));
        if (rr.IsCompileTimeConstant)
          return rr;
      }
      IType resultType = compilation.FindType(KnownTypeCode.Boolean);
      return BinaryOperatorResolveResult(resultType, lhs, op, rhs, isNullable);
    }
    
    /// <summary>
    /// Handle the case where an enum value is subtracted from another enum value
    /// U operator –(E x, E y);
    /// </summary>
    ResolveResult HandleEnumSubtraction(bool isNullable, IType enumType, ResolveResult lhs, ResolveResult rhs)
    {
      // evaluate as (U)((U)x – (U)y)
      IType elementType = GetEnumUnderlyingType(enumType);
      if (lhs.IsCompileTimeConstant && rhs.IsCompileTimeConstant && !isNullable && elementType.Kind != TypeKind.Enum) {
        var rr = ResolveBinaryOperator(BinaryOperatorType.Subtract, ResolveCast(elementType, lhs), ResolveCast(elementType, rhs));
        rr = WithCheckForOverflow(false).ResolveCast(elementType, rr);
        if (rr.IsCompileTimeConstant)
          return rr;
      }
      IType resultType = MakeNullable(elementType, isNullable);
      return BinaryOperatorResolveResult(resultType, lhs, BinaryOperatorType.Subtract, rhs, isNullable);
    }
    
    /// <summary>
    /// Handle the following enum operators:
    /// E operator +(E x, U y);
    /// E operator +(U x, E y);
    /// E operator –(E x, U y);
    /// E operator &amp;(E x, E y);
    /// E operator |(E x, E y);
    /// E operator ^(E x, E y);
    /// </summary>
    ResolveResult HandleEnumOperator(bool isNullable, IType enumType, BinaryOperatorType op, ResolveResult lhs, ResolveResult rhs)
    {
      // evaluate as (E)((U)x op (U)y)
      if (lhs.IsCompileTimeConstant && rhs.IsCompileTimeConstant && !isNullable) {
        IType elementType = GetEnumUnderlyingType(enumType);
        if (elementType.Kind != TypeKind.Enum) {
          var rr = ResolveBinaryOperator(op, ResolveCast(elementType, lhs), ResolveCast(elementType, rhs));
          rr = WithCheckForOverflow(false).ResolveCast(enumType, rr);
          if (rr.IsCompileTimeConstant) // only report result if it's a constant; use the regular OperatorResolveResult codepath otherwise
            return rr;
        }
      }
      IType resultType = MakeNullable(enumType, isNullable);
      return BinaryOperatorResolveResult(resultType, lhs, op, rhs, isNullable);
    }
    
    IType MakeNullable(IType type, bool isNullable)
    {
      if (isNullable)
        return NullableType.Create(compilation, type);
      else
        return type;
    }
    #endregion
    
    #region BinaryNumericPromotion
    bool BinaryNumericPromotion(bool isNullable, ref ResolveResult lhs, ref ResolveResult rhs, bool allowNullableConstants)
    {
      // C# 4.0 spec: §7.3.6.2
      TypeCode lhsCode = ReflectionHelper.GetTypeCode(NullableType.GetUnderlyingType(lhs.Type));
      TypeCode rhsCode = ReflectionHelper.GetTypeCode(NullableType.GetUnderlyingType(rhs.Type));
      // if one of the inputs is the null literal, promote that to the type of the other operand
      if (isNullable && lhs.Type.Kind == TypeKind.Null && rhsCode >= TypeCode.Boolean && rhsCode <= TypeCode.Decimal) {
        lhs = CastTo(rhsCode, isNullable, lhs, allowNullableConstants);
        lhsCode = rhsCode;
      } else if (isNullable && rhs.Type.Kind == TypeKind.Null && lhsCode >= TypeCode.Boolean && lhsCode <= TypeCode.Decimal) {
        rhs = CastTo(lhsCode, isNullable, rhs, allowNullableConstants);
        rhsCode = lhsCode;
      }
      bool bindingError = false;
      if (lhsCode >= TypeCode.Char && lhsCode <= TypeCode.Decimal
          && rhsCode >= TypeCode.Char && rhsCode <= TypeCode.Decimal)
      {
        TypeCode targetType;
        if (lhsCode == TypeCode.Decimal || rhsCode == TypeCode.Decimal) {
          targetType = TypeCode.Decimal;
          bindingError = (lhsCode == TypeCode.Single || lhsCode == TypeCode.Double
                          || rhsCode == TypeCode.Single || rhsCode == TypeCode.Double);
        } else if (lhsCode == TypeCode.Double || rhsCode == TypeCode.Double) {
          targetType = TypeCode.Double;
        } else if (lhsCode == TypeCode.Single || rhsCode == TypeCode.Single) {
          targetType = TypeCode.Single;
        } else if (lhsCode == TypeCode.UInt64 || rhsCode == TypeCode.UInt64) {
          targetType = TypeCode.UInt64;
          bindingError = IsSigned(lhsCode, lhs) || IsSigned(rhsCode, rhs);
        } else if (lhsCode == TypeCode.Int64 || rhsCode == TypeCode.Int64) {
          targetType = TypeCode.Int64;
        } else if (lhsCode == TypeCode.UInt32 || rhsCode == TypeCode.UInt32) {
          targetType = (IsSigned(lhsCode, lhs) || IsSigned(rhsCode, rhs)) ? TypeCode.Int64 : TypeCode.UInt32;
        } else {
          targetType = TypeCode.Int32;
        }
        lhs = CastTo(targetType, isNullable, lhs, allowNullableConstants);
        rhs = CastTo(targetType, isNullable, rhs, allowNullableConstants);
      }
      return !bindingError;
    }
    
    bool IsSigned(TypeCode code, ResolveResult rr)
    {
      // Determine whether the rr with code==ReflectionHelper.GetTypeCode(NullableType.GetUnderlyingType(rr.Type))
      // is a signed primitive type.
      switch (code) {
        case TypeCode.SByte:
        case TypeCode.Int16:
          return true;
        case TypeCode.Int32:
          // for int, consider implicit constant expression conversion
          if (rr.IsCompileTimeConstant && rr.ConstantValue != null && (int)rr.ConstantValue >= 0)
            return false;
          else
            return true;
        case TypeCode.Int64:
          // for long, consider implicit constant expression conversion
          if (rr.IsCompileTimeConstant && rr.ConstantValue != null && (long)rr.ConstantValue >= 0)
            return false;
          else
            return true;
        default:
          return false;
      }
    }
    
    ResolveResult CastTo(TypeCode targetType, bool isNullable, ResolveResult expression, bool allowNullableConstants)
    {
      IType elementType = compilation.FindType(targetType);
      IType nullableType = MakeNullable(elementType, isNullable);
      if (nullableType.Equals(expression.Type))
        return expression;
      if (allowNullableConstants && expression.IsCompileTimeConstant) {
        if (expression.ConstantValue == null)
          return new ConstantResolveResult(nullableType, null);
        ResolveResult rr = ResolveCast(elementType, expression);
        if (rr.IsError)
          return rr;
        Debug.Assert(rr.IsCompileTimeConstant);
        return new ConstantResolveResult(nullableType, rr.ConstantValue);
      } else {
        return Convert(expression, nullableType,
                       isNullable ? Conversion.ImplicitNullableConversion : Conversion.ImplicitNumericConversion);
      }
    }
    #endregion
    
    #region GetOverloadableOperatorName
    static string GetOverloadableOperatorName(BinaryOperatorType op)
    {
      switch (op) {
        case BinaryOperatorType.Add:
          return "op_Addition";
        case BinaryOperatorType.Subtract:
          return "op_Subtraction";
        case BinaryOperatorType.Multiply:
          return "op_Multiply";
        case BinaryOperatorType.Divide:
          return "op_Division";
        case BinaryOperatorType.Modulus:
          return "op_Modulus";
        case BinaryOperatorType.BitwiseAnd:
          return "op_BitwiseAnd";
        case BinaryOperatorType.BitwiseOr:
          return "op_BitwiseOr";
        case BinaryOperatorType.ExclusiveOr:
          return "op_ExclusiveOr";
        case BinaryOperatorType.ShiftLeft:
          return "op_LeftShift";
        case BinaryOperatorType.ShiftRight:
          return "op_RightShift";
        case BinaryOperatorType.Equality:
          return "op_Equality";
        case BinaryOperatorType.InEquality:
          return "op_Inequality";
        case BinaryOperatorType.GreaterThan:
          return "op_GreaterThan";
        case BinaryOperatorType.LessThan:
          return "op_LessThan";
        case BinaryOperatorType.GreaterThanOrEqual:
          return "op_GreaterThanOrEqual";
        case BinaryOperatorType.LessThanOrEqual:
          return "op_LessThanOrEqual";
        default:
          return null;
      }
    }
    #endregion
    
    #region Null coalescing operator
    ResolveResult ResolveNullCoalescingOperator(ResolveResult lhs, ResolveResult rhs)
    {
      if (NullableType.IsNullable(lhs.Type)) {
        IType a0 = NullableType.GetUnderlyingType(lhs.Type);
        if (TryConvert(ref rhs, a0)) {
          return BinaryOperatorResolveResult(a0, lhs, BinaryOperatorType.NullCoalescing, rhs);
        }
      }
      if (TryConvert(ref rhs, lhs.Type)) {
        return BinaryOperatorResolveResult(lhs.Type, lhs, BinaryOperatorType.NullCoalescing, rhs);
      }
      if (TryConvert(ref lhs, rhs.Type)) {
        return BinaryOperatorResolveResult(rhs.Type, lhs, BinaryOperatorType.NullCoalescing, rhs);
      } else {
        return new ErrorResolveResult(lhs.Type);
      }
    }
    #endregion
    #endregion
    
    #region Get user-defined operator candidates
    IEnumerable<IParameterizedMember> GetUserDefinedOperatorCandidates(IType type, string operatorName)
    {
      if (operatorName == null)
        return EmptyList<IMethod>.Instance;
      TypeCode c = ReflectionHelper.GetTypeCode(type);
      if (TypeCode.Boolean <= c && c <= TypeCode.Decimal || c == TypeCode.String) {
        // The .NET framework contains some of C#'s built-in operators as user-defined operators.
        // However, we must not use those as user-defined operators (we would skip numeric promotion).
        return EmptyList<IMethod>.Instance;
      }
      // C# 4.0 spec: §7.3.5 Candidate user-defined operators
      var operators = type.GetMethods(m => m.IsOperator && m.Name == operatorName).ToList();
      LiftUserDefinedOperators(operators);
      return operators;
    }
    
    void LiftUserDefinedOperators(List<IMethod> operators)
    {
      int nonLiftedMethodCount = operators.Count;
      // Construct lifted operators
      for (int i = 0; i < nonLiftedMethodCount; i++) {
        var liftedMethod = LiftUserDefinedOperator(operators[i]);
        if (liftedMethod != null)
          operators.Add(liftedMethod);
      }
    }
    
    LiftedUserDefinedOperator LiftUserDefinedOperator(IMethod m)
    {
      if (IsComparisonOperator(m)) {
        if (!m.ReturnType.Equals(compilation.FindType(KnownTypeCode.Boolean)))
          return null; // cannot lift this operator
      } else {
        if (!NullableType.IsNonNullableValueType(m.ReturnType))
          return null; // cannot lift this operator
      }
      for (int i = 0; i < m.Parameters.Count; i++) {
        if (!NullableType.IsNonNullableValueType(m.Parameters[i].Type))
          return null; // cannot lift this operator
      }
      return new LiftedUserDefinedOperator(m);
    }
    
    static bool IsComparisonOperator(IMethod m)
    {
      var type = OperatorDeclaration.GetOperatorType(m.Name);
      return type.HasValue && type.Value.IsComparisonOperator();
    }
    
    sealed class LiftedUserDefinedOperator : SpecializedMethod, OverloadResolution.ILiftedOperator
    {
      internal readonly IParameterizedMember nonLiftedOperator;
      
      public LiftedUserDefinedOperator(IMethod nonLiftedMethod)
        : base((IMethod)nonLiftedMethod.MemberDefinition, nonLiftedMethod.Substitution)
      {
        this.nonLiftedOperator = nonLiftedMethod;
        var substitution = new MakeNullableVisitor(nonLiftedMethod.Compilation, nonLiftedMethod.Substitution);
        this.Parameters = base.CreateParameters(substitution);
        // Comparison operators keep the 'bool' return type even when lifted.
        if (IsComparisonOperator(nonLiftedMethod))
          this.ReturnType = nonLiftedMethod.ReturnType;
        else
          this.ReturnType = nonLiftedMethod.ReturnType.AcceptVisitor(substitution);
      }
      
      public IList<IParameter> NonLiftedParameters {
        get { return nonLiftedOperator.Parameters; }
      }
      
      public override bool Equals(object obj)
      {
        LiftedUserDefinedOperator op = obj as LiftedUserDefinedOperator;
        return op != null && this.nonLiftedOperator.Equals(op.nonLiftedOperator);
      }
      
      public override int GetHashCode()
      {
        return nonLiftedOperator.GetHashCode() ^ 0x7191254;
      }
    }
    
    sealed class MakeNullableVisitor : TypeVisitor
    {
      readonly ICompilation compilation;
      readonly TypeParameterSubstitution typeParameterSubstitution;
      
      public MakeNullableVisitor(ICompilation compilation, TypeParameterSubstitution typeParameterSubstitution)
      {
        this.compilation = compilation;
        this.typeParameterSubstitution = typeParameterSubstitution;
      }
      
      public override IType VisitTypeDefinition(ITypeDefinition type)
      {
        return NullableType.Create(compilation, type.AcceptVisitor(typeParameterSubstitution));
      }
      
      public override IType VisitTypeParameter(ITypeParameter type)
      {
        return NullableType.Create(compilation, type.AcceptVisitor(typeParameterSubstitution));
      }
      
      public override IType VisitParameterizedType(ParameterizedType type)
      {
        return NullableType.Create(compilation, type.AcceptVisitor(typeParameterSubstitution));
      }
      
      public override IType VisitOtherType(IType type)
      {
        return NullableType.Create(compilation, type.AcceptVisitor(typeParameterSubstitution));
      }
    }
    
    ResolveResult CreateResolveResultForUserDefinedOperator(OverloadResolution r, System.Linq.Expressions.ExpressionType operatorType)
    {
      if (r.BestCandidateErrors != OverloadResolutionErrors.None)
        return r.CreateResolveResult(null);
      IMethod method = (IMethod)r.BestCandidate;
      return new OperatorResolveResult(method.ReturnType, operatorType, method,
                                       isLiftedOperator: method is OverloadResolution.ILiftedOperator,
                                       operands: r.GetArgumentsWithConversions());
    }
    #endregion
    
    #region ResolveCast
    bool TryConvert(ref ResolveResult rr, IType targetType)
    {
      Conversion c = conversions.ImplicitConversion(rr, targetType);
      if (c.IsValid) {
        rr = Convert(rr, targetType, c);
        return true;
      } else {
        return false;
      }
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="rr">The input resolve result that should be converted.
    /// If a conversion exists, it is applied to the resolve result</param>
    /// <param name="targetType">The target type that we should convert to</param>
    /// <param name="isNullable">Whether we are dealing with a lifted operator</param>
    /// <param name="enumRR">The resolve result that is enum-typed.
    /// If necessary, a nullable conversion is applied.</param>
    /// <param name="allowConversionFromConstantZero">
    /// Whether the conversion from the constant zero is allowed.
    /// </param>
    /// <returns>True if the conversion is successful; false otherwise.
    /// If the conversion is not successful, the ref parameters will not be modified.</returns>
    bool TryConvertEnum(ref ResolveResult rr, IType targetType, ref bool isNullable, ref ResolveResult enumRR, bool allowConversionFromConstantZero = true)
    {
      Conversion c;
      if (!isNullable) {
        // Try non-nullable
        c = conversions.ImplicitConversion(rr, targetType);
        if (c.IsValid && (allowConversionFromConstantZero || !c.IsEnumerationConversion)) {
          rr = Convert(rr, targetType, c);
          return true;
        }
      }
      // make targetType nullable if it isn't already:
      if (!targetType.IsKnownType(KnownTypeCode.NullableOfT))
        targetType = NullableType.Create(compilation, targetType);
      
      c = conversions.ImplicitConversion(rr, targetType);
      if (c.IsValid && (allowConversionFromConstantZero || !c.IsEnumerationConversion)) {
        rr = Convert(rr, targetType, c);
        isNullable = true;
        // Also convert the enum-typed RR to nullable, if it isn't already
        if (!enumRR.Type.IsKnownType(KnownTypeCode.NullableOfT)) {
          var nullableType = NullableType.Create(compilation, enumRR.Type);
          enumRR = new ConversionResolveResult(nullableType, enumRR, Conversion.ImplicitNullableConversion);
        }
        return true;
      }
      return false;
    }
    
    ResolveResult Convert(ResolveResult rr, IType targetType)
    {
      return Convert(rr, targetType, conversions.ImplicitConversion(rr, targetType));
    }
    
    ResolveResult Convert(ResolveResult rr, IType targetType, Conversion c)
    {
      if (c == Conversion.IdentityConversion)
        return rr;
      else if (rr.IsCompileTimeConstant && c != Conversion.None && !c.IsUserDefined)
        return ResolveCast(targetType, rr);
      else
        return new ConversionResolveResult(targetType, rr, c, checkForOverflow);
    }
    
    public ResolveResult ResolveCast(IType targetType, ResolveResult expression)
    {
      // C# 4.0 spec: §7.7.6 Cast expressions
      Conversion c = conversions.ExplicitConversion(expression, targetType);
      if (expression.IsCompileTimeConstant && !c.IsUserDefined) {
        TypeCode code = ReflectionHelper.GetTypeCode(targetType);
        if (code >= TypeCode.Boolean && code <= TypeCode.Decimal && expression.ConstantValue != null) {
          try {
            return new ConstantResolveResult(targetType, CSharpPrimitiveCast(code, expression.ConstantValue));
          } catch (OverflowException) {
            return new ErrorResolveResult(targetType);
          } catch (InvalidCastException) {
            return new ErrorResolveResult(targetType);
          }
        } else if (code == TypeCode.String) {
          if (expression.ConstantValue == null || expression.ConstantValue is string)
            return new ConstantResolveResult(targetType, expression.ConstantValue);
          else
            return new ErrorResolveResult(targetType);
        } else if (targetType.Kind == TypeKind.Enum) {
          code = ReflectionHelper.GetTypeCode(GetEnumUnderlyingType(targetType));
          if (code >= TypeCode.SByte && code <= TypeCode.UInt64 && expression.ConstantValue != null) {
            try {
              return new ConstantResolveResult(targetType, CSharpPrimitiveCast(code, expression.ConstantValue));
            } catch (OverflowException) {
              return new ErrorResolveResult(targetType);
            } catch (InvalidCastException) {
              return new ErrorResolveResult(targetType);
            }
          }
        }
      }
      return new ConversionResolveResult(targetType, expression, c, checkForOverflow);
    }
    
    internal object CSharpPrimitiveCast(TypeCode targetType, object input)
    {
      return Utils.CSharpPrimitiveCast.Cast(targetType, input, this.CheckForOverflow);
    }
    #endregion
    
    #region ResolveSimpleName
    public ResolveResult ResolveSimpleName(string identifier, IList<IType> typeArguments, bool isInvocationTarget = false)
    {
      // C# 4.0 spec: §7.6.2 Simple Names
      
      return LookupSimpleNameOrTypeName(
        identifier, typeArguments,
        isInvocationTarget ? NameLookupMode.InvocationTarget : NameLookupMode.Expression);
    }
    
    public ResolveResult LookupSimpleNameOrTypeName(string identifier, IList<IType> typeArguments, NameLookupMode lookupMode)
    {
      // C# 4.0 spec: §3.8 Namespace and type names; §7.6.2 Simple Names
      
      if (identifier == null)
        throw new ArgumentNullException("identifier");
      if (typeArguments == null)
        throw new ArgumentNullException("typeArguments");
      
      int k = typeArguments.Count;
      
      if (k == 0) {
        if (lookupMode == NameLookupMode.Expression || lookupMode == NameLookupMode.InvocationTarget) {
          // Look in local variables
          foreach (IVariable v in this.LocalVariables) {
            if (v.Name == identifier) {
              return new LocalResolveResult(v);
            }
          }
          // Look in parameters of current method
          IParameterizedMember parameterizedMember = this.CurrentMember as IParameterizedMember;
          if (parameterizedMember != null) {
            foreach (IParameter p in parameterizedMember.Parameters) {
              if (p.Name == identifier) {
                return new LocalResolveResult(p);
              }
            }
          }
        }
        
        // look in type parameters of current method
        IMethod m = this.CurrentMember as IMethod;
        if (m != null) {
          foreach (ITypeParameter tp in m.TypeParameters) {
            if (tp.Name == identifier)
              return new TypeResolveResult(tp);
          }
        }
      }
      
      bool parameterizeResultType = !(typeArguments.Count != 0 && typeArguments.All(t => t.Kind == TypeKind.UnboundTypeArgument));
      
      ResolveResult r = null;
      if (currentTypeDefinitionCache != null) {
        Dictionary<string, ResolveResult> cache = null;
        bool foundInCache = false;
        if (k == 0) {
          switch (lookupMode) {
            case NameLookupMode.Expression:
              cache = currentTypeDefinitionCache.SimpleNameLookupCacheExpression;
              break;
            case NameLookupMode.InvocationTarget:
              cache = currentTypeDefinitionCache.SimpleNameLookupCacheInvocationTarget;
              break;
            case NameLookupMode.Type:
              cache = currentTypeDefinitionCache.SimpleTypeLookupCache;
              break;
          }
          if (cache != null) {
            lock (cache)
              foundInCache = cache.TryGetValue(identifier, out r);
          }
        }
        if (foundInCache) {
          r = (r != null ? r.ShallowClone() : null);
        } else {
          r = LookInCurrentType(identifier, typeArguments, lookupMode, parameterizeResultType);
          if (cache != null) {
            // also cache missing members (r==null)
            lock (cache)
              cache[identifier] = r;
          }
        }
        if (r != null)
          return r;
      }
      
      if (context.CurrentUsingScope == null) {
        // If no using scope was specified, we still need to look in the global namespace:
        r = LookInUsingScopeNamespace(null, compilation.RootNamespace, identifier, typeArguments, parameterizeResultType);
      } else {
        if (k == 0 && lookupMode != NameLookupMode.TypeInUsingDeclaration) {
          if (context.CurrentUsingScope.ResolveCache.TryGetValue(identifier, out r)) {
            r = (r != null ? r.ShallowClone() : null);
          } else {
            r = LookInCurrentUsingScope(identifier, typeArguments, false, false);
            context.CurrentUsingScope.ResolveCache.TryAdd(identifier, r);
          }
        } else {
          r = LookInCurrentUsingScope(identifier, typeArguments, lookupMode == NameLookupMode.TypeInUsingDeclaration, parameterizeResultType);
        }
      }
      if (r != null)
        return r;
      
      if (typeArguments.Count == 0 && identifier == "dynamic") {
        return new TypeResolveResult(SpecialType.Dynamic);
      } else {
        return new UnknownIdentifierResolveResult(identifier, typeArguments.Count);
      }
    }
    
    public bool IsVariableReferenceWithSameType (ResolveResult rr, string identifier, out TypeResolveResult trr)
    {
      if (!(rr is MemberResolveResult || rr is LocalResolveResult)) {
        trr = null;
        return false;
      }
      trr = LookupSimpleNameOrTypeName (identifier, EmptyList<IType>.Instance, NameLookupMode.Type) as TypeResolveResult;
      return trr != null && trr.Type.Equals (rr.Type);
    }
    
    ResolveResult LookInCurrentType(string identifier, IList<IType> typeArguments, NameLookupMode lookupMode, bool parameterizeResultType)
    {
      int k = typeArguments.Count;
      MemberLookup lookup = CreateMemberLookup(lookupMode);
      // look in current type definitions
      for (ITypeDefinition t = this.CurrentTypeDefinition; t != null; t = t.DeclaringTypeDefinition) {
        if (k == 0) {
          // Look for type parameter with that name
          var typeParameters = t.TypeParameters;
          // Look at all type parameters, including those copied from outer classes,
          // so that we can fetch the version with the correct owner.
          for (int i = 0; i < typeParameters.Count; i++) {
            if (typeParameters[i].Name == identifier)
              return new TypeResolveResult(typeParameters[i]);
          }
        }
        
        if (lookupMode == NameLookupMode.BaseTypeReference && t == this.CurrentTypeDefinition) {
          // don't look in current type when resolving a base type reference
          continue;
        }
        
        ResolveResult r;
        if (lookupMode == NameLookupMode.Expression || lookupMode == NameLookupMode.InvocationTarget) {
          var targetResolveResult = (t == this.CurrentTypeDefinition ? ResolveThisReference() : new TypeResolveResult(t));
          r = lookup.Lookup(targetResolveResult, identifier, typeArguments, lookupMode == NameLookupMode.InvocationTarget);
        } else {
          r = lookup.LookupType(t, identifier, typeArguments, parameterizeResultType);
        }
        if (!(r is UnknownMemberResolveResult)) // but do return AmbiguousMemberResolveResult
          return r;
      }
      return null;
    }
    
    ResolveResult LookInCurrentUsingScope(string identifier, IList<IType> typeArguments, bool isInUsingDeclaration, bool parameterizeResultType)
    {
      // look in current namespace definitions
      ResolvedUsingScope currentUsingScope = this.CurrentUsingScope;
      for (ResolvedUsingScope u = currentUsingScope; u != null; u = u.Parent) {
        var resultInNamespace = LookInUsingScopeNamespace(u, u.Namespace, identifier, typeArguments, parameterizeResultType);
        if (resultInNamespace != null)
          return resultInNamespace;
        // then look for aliases:
        if (typeArguments.Count == 0) {
          if (u.ExternAliases.Contains(identifier)) {
            return ResolveExternAlias(identifier);
          }
          if (!(isInUsingDeclaration && u == currentUsingScope)) {
            foreach (var pair in u.UsingAliases) {
              if (pair.Key == identifier) {
                return pair.Value.ShallowClone();
              }
            }
          }
        }
        // finally, look in the imported namespaces:
        if (!(isInUsingDeclaration && u == currentUsingScope)) {
          IType firstResult = null;
          foreach (var importedNamespace in u.Usings) {
            ITypeDefinition def = importedNamespace.GetTypeDefinition(identifier, typeArguments.Count);
            if (def != null) {
              IType resultType;
              if (parameterizeResultType && typeArguments.Count > 0)
                resultType = new ParameterizedType(def, typeArguments);
              else
                resultType = def;
              
              if (firstResult == null || !TopLevelTypeDefinitionIsAccessible(firstResult.GetDefinition())) {
                if (TopLevelTypeDefinitionIsAccessible(resultType.GetDefinition()))
                  firstResult = resultType;
              } else if (TopLevelTypeDefinitionIsAccessible(def)) {
                return new AmbiguousTypeResolveResult(firstResult);
              }
            }
          }
          if (firstResult != null)
            return new TypeResolveResult(firstResult);
        }
        // if we didn't find anything: repeat lookup with parent namespace
      }
      return null;
    }

    ResolveResult LookInUsingScopeNamespace(ResolvedUsingScope usingScope, INamespace n, string identifier, IList<IType> typeArguments, bool parameterizeResultType)
    {
      if (n == null)
        return null;
      // first look for a namespace
      int k = typeArguments.Count;
      if (k == 0) {
        INamespace childNamespace = n.GetChildNamespace(identifier);
        if (childNamespace != null) {
          if (usingScope != null && usingScope.HasAlias(identifier))
            return new AmbiguousTypeResolveResult(new UnknownType(null, identifier));
          return new NamespaceResolveResult(childNamespace);
        }
      }
      // then look for a type
      ITypeDefinition def = n.GetTypeDefinition(identifier, k);
      if (def != null) {
        IType result = def;
        if (parameterizeResultType && k > 0) {
          result = new ParameterizedType(def, typeArguments);
        }
        if (usingScope != null && usingScope.HasAlias(identifier))
          return new AmbiguousTypeResolveResult(result);
        else
          return new TypeResolveResult(result);
      }
      return null;
    }
    
    bool TopLevelTypeDefinitionIsAccessible(ITypeDefinition typeDef)
    {
      if (typeDef.IsInternal) {
        return typeDef.ParentAssembly.InternalsVisibleTo(compilation.MainAssembly);
      }
      return true;
    }
    
    /// <summary>
    /// Looks up an alias (identifier in front of :: operator)
    /// </summary>
    public ResolveResult ResolveAlias(string identifier)
    {
      if (identifier == "global")
        return new NamespaceResolveResult(compilation.RootNamespace);
      
      for (ResolvedUsingScope n = this.CurrentUsingScope; n != null; n = n.Parent) {
        if (n.ExternAliases.Contains(identifier)) {
          return ResolveExternAlias(identifier);
        }
        foreach (var pair in n.UsingAliases) {
          if (pair.Key == identifier) {
            return (pair.Value as NamespaceResolveResult) ?? ErrorResult;
          }
        }
      }
      return ErrorResult;
    }
    
    ResolveResult ResolveExternAlias(string alias)
    {
      INamespace ns = compilation.GetNamespaceForExternAlias(alias);
      if (ns != null)
        return new NamespaceResolveResult(ns);
      else
        return ErrorResult;
    }
    #endregion
    
    #region ResolveMemberAccess
    public ResolveResult ResolveMemberAccess(ResolveResult target, string identifier, IList<IType> typeArguments, NameLookupMode lookupMode = NameLookupMode.Expression)
    {
      // C# 4.0 spec: §7.6.4
      
      bool parameterizeResultType = !(typeArguments.Count != 0 && typeArguments.All(t => t.Kind == TypeKind.UnboundTypeArgument));
      NamespaceResolveResult nrr = target as NamespaceResolveResult;
      if (nrr != null) {
        return ResolveMemberAccessOnNamespace(nrr, identifier, typeArguments, parameterizeResultType);
      }
      
      if (target.Type.Kind == TypeKind.Dynamic)
        return new DynamicMemberResolveResult(target, identifier);
      
      MemberLookup lookup = CreateMemberLookup(lookupMode);
      ResolveResult result;
      switch (lookupMode) {
        case NameLookupMode.Expression:
          result = lookup.Lookup(target, identifier, typeArguments, isInvocation: false);
          break;
        case NameLookupMode.InvocationTarget:
          result = lookup.Lookup(target, identifier, typeArguments, isInvocation: true);
          break;
        case NameLookupMode.Type:
        case NameLookupMode.TypeInUsingDeclaration:
        case NameLookupMode.BaseTypeReference:
          // Don't do the UnknownMemberResolveResult/MethodGroupResolveResult processing,
          // it's only relevant for expressions.
          return lookup.LookupType(target.Type, identifier, typeArguments, parameterizeResultType);
        default:
          throw new NotSupportedException("Invalid value for NameLookupMode");
      }
      if (result is UnknownMemberResolveResult) {
        // We intentionally use all extension methods here, not just the eligible ones.
        // Proper eligibility checking is only possible for the full invocation
        // (after we know the remaining arguments).
        // The eligibility check in GetExtensionMethods is only intended for code completion.
        var extensionMethods = GetExtensionMethods(identifier, typeArguments);
        if (extensionMethods.Count > 0) {
          return new MethodGroupResolveResult(target, identifier, EmptyList<MethodListWithDeclaringType>.Instance, typeArguments) {
            extensionMethods = extensionMethods
          };
        }
      } else {
        MethodGroupResolveResult mgrr = result as MethodGroupResolveResult;
        if (mgrr != null) {
          Debug.Assert(mgrr.extensionMethods == null);
          // set the values that are necessary to make MethodGroupResolveResult.GetExtensionMethods() work
          mgrr.resolver = this;
        }
      }
      return result;
    }
    
    [Obsolete("Use ResolveMemberAccess() with NameLookupMode.Type instead")]
    public ResolveResult ResolveMemberType(ResolveResult target, string identifier, IList<IType> typeArguments)
    {
      return ResolveMemberAccess(target, identifier, typeArguments, NameLookupMode.Type);
    }
    
    ResolveResult ResolveMemberAccessOnNamespace(NamespaceResolveResult nrr, string identifier, IList<IType> typeArguments, bool parameterizeResultType)
    {
      if (typeArguments.Count == 0) {
        INamespace childNamespace = nrr.Namespace.GetChildNamespace(identifier);
        if (childNamespace != null)
          return new NamespaceResolveResult(childNamespace);
      }
      ITypeDefinition def = nrr.Namespace.GetTypeDefinition(identifier, typeArguments.Count);
      if (def != null) {
        if (parameterizeResultType && typeArguments.Count > 0)
          return new TypeResolveResult(new ParameterizedType(def, typeArguments));
        else
          return new TypeResolveResult(def);
      }
      return ErrorResult;
    }
    
    /// <summary>
    /// Creates a MemberLookup instance using this resolver's settings.
    /// </summary>
    public MemberLookup CreateMemberLookup()
    {
      ITypeDefinition currentTypeDefinition = this.CurrentTypeDefinition;
      bool isInEnumMemberInitializer = this.CurrentMember != null && this.CurrentMember.SymbolKind == SymbolKind.Field
        && currentTypeDefinition != null && currentTypeDefinition.Kind == TypeKind.Enum;
      return new MemberLookup(currentTypeDefinition, this.Compilation.MainAssembly, isInEnumMemberInitializer);
    }
    
    /// <summary>
    /// Creates a MemberLookup instance using this resolver's settings.
    /// </summary>
    public MemberLookup CreateMemberLookup(NameLookupMode lookupMode)
    {
      if (lookupMode == NameLookupMode.BaseTypeReference && this.CurrentTypeDefinition != null) {
        // When looking up a base type reference, treat us as being outside the current type definition
        // for accessibility purposes.
        // This avoids a stack overflow when referencing a protected class nested inside the base class
        // of a parent class. (NameLookupTests.InnerClassInheritingFromProtectedBaseInnerClassShouldNotCauseStackOverflow)
        return new MemberLookup(this.CurrentTypeDefinition.DeclaringTypeDefinition, this.Compilation.MainAssembly, false);
      } else {
        return CreateMemberLookup();
      }
    }
    #endregion
    
    #region ResolveIdentifierInObjectInitializer
    public ResolveResult ResolveIdentifierInObjectInitializer(string identifier)
    {
      MemberLookup memberLookup = CreateMemberLookup();
      return memberLookup.Lookup(this.CurrentObjectInitializer, identifier, EmptyList<IType>.Instance, false);
    }
    #endregion
    
    #region GetExtensionMethods
    /// <summary>
    /// Gets all extension methods that are available in the current context.
    /// </summary>
    /// <param name="name">Name of the extension method. Pass null to retrieve all extension methods.</param>
    /// <param name="typeArguments">Explicitly provided type arguments.
    /// An empty list will return all matching extension method definitions;
    /// a non-empty list will return <see cref="SpecializedMethod"/>s for all extension methods
    /// with the matching number of type parameters.</param>
    /// <remarks>
    /// The results are stored in nested lists because they are grouped by using scope.
    /// That is, for "using SomeExtensions; namespace X { using MoreExtensions; ... }",
    /// the return value will be
    /// new List {
    ///    new List { all extensions from MoreExtensions },
    ///    new List { all extensions from SomeExtensions }
    /// }
    /// </remarks>
    public List<List<IMethod>> GetExtensionMethods(string name = null, IList<IType> typeArguments = null)
    {
      return GetExtensionMethods(null, name, typeArguments);
    }
    
    /// <summary>
    /// Gets the extension methods that are called 'name'
    /// and are applicable with a first argument type of 'targetType'.
    /// </summary>
    /// <param name="targetType">Type of the 'this' argument</param>
    /// <param name="name">Name of the extension method. Pass null to retrieve all extension methods.</param>
    /// <param name="typeArguments">Explicitly provided type arguments.
    /// An empty list will return all matching extension method definitions;
    /// a non-empty list will return <see cref="SpecializedMethod"/>s for all extension methods
    /// with the matching number of type parameters.</param>
    /// <param name="substituteInferredTypes">
    /// Specifies whether to produce a <see cref="SpecializedMethod"/>
    /// when type arguments could be inferred from <paramref name="targetType"/>. This parameter
    /// is only used for inferred types and has no effect if <paramref name="typeArguments"/> is non-empty.
    /// </param>
    /// <remarks>
    /// The results are stored in nested lists because they are grouped by using scope.
    /// That is, for "using SomeExtensions; namespace X { using MoreExtensions; ... }",
    /// the return value will be
    /// new List {
    ///    new List { all extensions from MoreExtensions },
    ///    new List { all extensions from SomeExtensions }
    /// }
    /// </remarks>
    public List<List<IMethod>> GetExtensionMethods(IType targetType, string name = null, IList<IType> typeArguments = null, bool substituteInferredTypes = false)
    {
      var lookup = CreateMemberLookup();
      List<List<IMethod>> extensionMethodGroups = new List<List<IMethod>>();
      foreach (var inputGroup in GetAllExtensionMethods(lookup)) {
        List<IMethod> outputGroup = new List<IMethod>();
        foreach (var method in inputGroup) {
          if (name != null && method.Name != name)
            continue;
          if (!lookup.IsAccessible(method, false))
            continue;
          IType[] inferredTypes;
          if (typeArguments != null && typeArguments.Count > 0) {
            if (method.TypeParameters.Count != typeArguments.Count)
              continue;
            var sm = method.Specialize(new TypeParameterSubstitution(null, typeArguments));
            if (IsEligibleExtensionMethod(compilation, conversions, targetType, sm, false, out inferredTypes))
              outputGroup.Add(sm);
          } else {
            if (IsEligibleExtensionMethod(compilation, conversions, targetType, method, true, out inferredTypes)) {
              if (substituteInferredTypes && inferredTypes != null) {
                outputGroup.Add(method.Specialize(new TypeParameterSubstitution(null, inferredTypes)));
              } else {
                outputGroup.Add(method);
              }
            }
          }
        }
        if (outputGroup.Count > 0)
          extensionMethodGroups.Add(outputGroup);
      }
      return extensionMethodGroups;
    }
    
    /// <summary>
    /// Checks whether the specified extension method is eligible on the target type.
    /// </summary>
    /// <param name="targetType">Target type that is passed as first argument to the extension method.</param>
    /// <param name="method">The extension method.</param>
    /// <param name="useTypeInference">Whether to perform type inference for the method.
    /// Use <c>false</c> if <paramref name="method"/> is already parameterized (e.g. when type arguments were given explicitly).
    /// Otherwise, use <c>true</c>.
    /// </param>
    /// <param name="outInferredTypes">If the method is generic and <paramref name="useTypeInference"/> is <c>true</c>,
    /// and at least some of the type arguments could be inferred, this parameter receives the inferred type arguments.
    /// Since only the type for the first parameter is considered, not all type arguments may be inferred.
    /// If an array is returned, any slot with an uninferred type argument will be set to the method's
    /// corresponding type parameter.
    /// </param>
    public static bool IsEligibleExtensionMethod(IType targetType, IMethod method, bool useTypeInference, out IType[] outInferredTypes)
    {
      if (targetType == null)
        throw new ArgumentNullException("targetType");
      if (method == null)
        throw new ArgumentNullException("method");
      var compilation = method.Compilation;
      return IsEligibleExtensionMethod(compilation, CSharpConversions.Get(compilation), targetType, method, useTypeInference, out outInferredTypes);
    }
    
    static bool IsEligibleExtensionMethod(ICompilation compilation, CSharpConversions conversions, IType targetType, IMethod method, bool useTypeInference, out IType[] outInferredTypes)
    {
      outInferredTypes = null;
      if (targetType == null)
        return true;
      if (method.Parameters.Count == 0)
        return false;
      IType thisParameterType = method.Parameters[0].Type;
      if (useTypeInference && method.TypeParameters.Count > 0) {
        // We need to infer type arguments from targetType:
        TypeInference ti = new TypeInference(compilation, conversions);
        ResolveResult[] arguments = { new ResolveResult(targetType) };
        IType[] parameterTypes = { method.Parameters[0].Type };
        bool success;
        var inferredTypes = ti.InferTypeArguments(method.TypeParameters, arguments, parameterTypes, out success);
        var substitution = new TypeParameterSubstitution(null, inferredTypes);
        // Validate that the types that could be inferred (aren't unknown) satisfy the constraints:
        bool hasInferredTypes = false;
        for (int i = 0; i < inferredTypes.Length; i++) {
          if (inferredTypes[i].Kind != TypeKind.Unknown && inferredTypes[i].Kind != TypeKind.UnboundTypeArgument) {
            hasInferredTypes = true;
            if (!OverloadResolution.ValidateConstraints(method.TypeParameters[i], inferredTypes[i], substitution, conversions))
              return false;
          } else {
            inferredTypes[i] = method.TypeParameters[i]; // do not substitute types that could not be inferred
          }
        }
        if (hasInferredTypes)
          outInferredTypes = inferredTypes;
        thisParameterType = thisParameterType.AcceptVisitor(substitution);
      }
      Conversion c = conversions.ImplicitConversion(targetType, thisParameterType);
      return c.IsValid && (c.IsIdentityConversion || c.IsReferenceConversion || c.IsBoxingConversion);
    }
    
    /// <summary>
    /// Gets all extension methods available in the current using scope.
    /// This list includes inaccessible methods.
    /// </summary>
    IList<List<IMethod>> GetAllExtensionMethods(MemberLookup lookup)
    {
      var currentUsingScope = context.CurrentUsingScope;
      if (currentUsingScope == null)
        return EmptyList<List<IMethod>>.Instance;
      List<List<IMethod>> extensionMethodGroups = LazyInit.VolatileRead(ref currentUsingScope.AllExtensionMethods);
      if (extensionMethodGroups != null) {
        return extensionMethodGroups;
      }
      extensionMethodGroups = new List<List<IMethod>>();
      List<IMethod> m;
      for (ResolvedUsingScope scope = currentUsingScope; scope != null; scope = scope.Parent) {
        INamespace ns = scope.Namespace;
        if (ns != null) {
          m = GetExtensionMethods(lookup, ns).ToList();
          if (m.Count > 0)
            extensionMethodGroups.Add(m);
        }
        
        m = scope.Usings
          .Distinct()
          .SelectMany(importedNamespace =>  GetExtensionMethods(lookup, importedNamespace))
          .ToList();
        if (m.Count > 0)
          extensionMethodGroups.Add(m);
      }
      return LazyInit.GetOrSet(ref currentUsingScope.AllExtensionMethods, extensionMethodGroups);
    }
    
    IEnumerable<IMethod> GetExtensionMethods(MemberLookup lookup, INamespace ns)
    {
      // TODO: maybe make this a property on INamespace?
      return
        from c in ns.Types
        where c.IsStatic && c.HasExtensionMethods && c.TypeParameters.Count == 0 && lookup.IsAccessible(c, false)
        from m in c.Methods
        where m.IsExtensionMethod
        select m;
    }
    #endregion
    
    #region ResolveInvocation

    IList<ResolveResult> AddArgumentNamesIfNecessary(ResolveResult[] arguments, string[] argumentNames) {
      if (argumentNames == null) {
        return arguments;
      }
      else {
        var result = new ResolveResult[arguments.Length];
        for (int i = 0; i < arguments.Length; i++) {
          result[i] = (argumentNames[i] != null ? new NamedArgumentResolveResult(argumentNames[i], arguments[i]) : arguments[i]);
        }
        return result;
      }
    }

    private ResolveResult ResolveInvocation(ResolveResult target, ResolveResult[] arguments, string[] argumentNames, bool allowOptionalParameters)
    {
      // C# 4.0 spec: §7.6.5
      
      if (target.Type.Kind == TypeKind.Dynamic) {
        return new DynamicInvocationResolveResult(target, DynamicInvocationType.Invocation, AddArgumentNamesIfNecessary(arguments, argumentNames));
      }
      
      bool isDynamic = arguments.Any(a => a.Type.Kind == TypeKind.Dynamic);
      MethodGroupResolveResult mgrr = target as MethodGroupResolveResult;
      if (mgrr != null) {
        if (isDynamic) {
          // If we have dynamic arguments, we need to represent the invocation as a dynamic invocation if there is more than one applicable method.
          var or2 = CreateOverloadResolution(arguments, argumentNames, mgrr.TypeArguments.ToArray());
          var applicableMethods = mgrr.MethodsGroupedByDeclaringType.SelectMany(m => m, (x, m) => new { x.DeclaringType, Method = m }).Where(x => OverloadResolution.IsApplicable(or2.AddCandidate(x.Method))).ToList();

          if (applicableMethods.Count > 1) {
            ResolveResult actualTarget;
            if (applicableMethods.All(x => x.Method.IsStatic) && !(mgrr.TargetResult is TypeResolveResult))
              actualTarget = new TypeResolveResult(mgrr.TargetType);
            else
              actualTarget = mgrr.TargetResult;

            var l = new List<MethodListWithDeclaringType>();
            foreach (var m in applicableMethods) {
              if (l.Count == 0 || l[l.Count - 1].DeclaringType != m.DeclaringType)
                l.Add(new MethodListWithDeclaringType(m.DeclaringType));
              l[l.Count - 1].Add(m.Method);
            }
            return new DynamicInvocationResolveResult(new MethodGroupResolveResult(actualTarget, mgrr.MethodName, l, mgrr.TypeArguments), DynamicInvocationType.Invocation, AddArgumentNamesIfNecessary(arguments, argumentNames));
          }
        }

        OverloadResolution or = mgrr.PerformOverloadResolution(compilation, arguments, argumentNames, checkForOverflow: checkForOverflow, conversions: conversions, allowOptionalParameters: allowOptionalParameters);
        if (or.BestCandidate != null) {
          if (or.BestCandidate.IsStatic && !or.IsExtensionMethodInvocation && !(mgrr.TargetResult is TypeResolveResult))
            return or.CreateResolveResult(new TypeResolveResult(mgrr.TargetType), returnTypeOverride: isDynamic ? SpecialType.Dynamic : null);
          else
            return or.CreateResolveResult(mgrr.TargetResult, returnTypeOverride: isDynamic ? SpecialType.Dynamic : null);
        } else {
          // No candidate found at all (not even an inapplicable one).
          // This can happen with empty method groups (as sometimes used with extension methods)
          return new UnknownMethodResolveResult(
            mgrr.TargetType, mgrr.MethodName, mgrr.TypeArguments, CreateParameters(arguments, argumentNames));
        }
      }
      UnknownMemberResolveResult umrr = target as UnknownMemberResolveResult;
      if (umrr != null) {
        return new UnknownMethodResolveResult(umrr.TargetType, umrr.MemberName, umrr.TypeArguments, CreateParameters(arguments, argumentNames));
      }
      UnknownIdentifierResolveResult uirr = target as UnknownIdentifierResolveResult;
      if (uirr != null && CurrentTypeDefinition != null) {
        return new UnknownMethodResolveResult(CurrentTypeDefinition, uirr.Identifier, EmptyList<IType>.Instance, CreateParameters(arguments, argumentNames));
      }
      IMethod invokeMethod = target.Type.GetDelegateInvokeMethod();
      if (invokeMethod != null) {
        OverloadResolution or = CreateOverloadResolution(arguments, argumentNames);
        or.AddCandidate(invokeMethod);
        return new CSharpInvocationResolveResult(
          target, invokeMethod, //invokeMethod.ReturnType.Resolve(context),
          or.GetArgumentsWithConversionsAndNames(), or.BestCandidateErrors,
          isExpandedForm: or.BestCandidateIsExpandedForm,
          isDelegateInvocation: true,
          argumentToParameterMap: or.GetArgumentToParameterMap(),
          returnTypeOverride: isDynamic ? SpecialType.Dynamic : null);
      }
      return ErrorResult;
    }

    /// <summary>
    /// Resolves an invocation.
    /// </summary>
    /// <param name="target">The target of the invocation. Usually a MethodGroupResolveResult.</param>
    /// <param name="arguments">
    /// Arguments passed to the method.
    /// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
    /// </param>
    /// <param name="argumentNames">
    /// The argument names. Pass the null string for positional arguments.
    /// </param>
    /// <returns>InvocationResolveResult or UnknownMethodResolveResult</returns>
    public ResolveResult ResolveInvocation(ResolveResult target, ResolveResult[] arguments, string[] argumentNames = null)
    {
      return ResolveInvocation(target, arguments, argumentNames, allowOptionalParameters: true);
    }
    
    List<IParameter> CreateParameters(ResolveResult[] arguments, string[] argumentNames)
    {
      List<IParameter> list = new List<IParameter>();
      if (argumentNames == null) {
        argumentNames = new string[arguments.Length];
      } else {
        if (argumentNames.Length != arguments.Length)
          throw new ArgumentException();
        argumentNames = (string[])argumentNames.Clone();
      }
      for (int i = 0; i < arguments.Length; i++) {
        // invent argument names where necessary:
        if (argumentNames[i] == null) {
          string newArgumentName = GuessParameterName(arguments[i]);
          if (argumentNames.Contains(newArgumentName)) {
            // disambiguate argument name (e.g. add a number)
            int num = 1;
            string newName;
            do {
              newName = newArgumentName + num.ToString();
              num++;
            } while(argumentNames.Contains(newName));
            newArgumentName = newName;
          }
          argumentNames[i] = newArgumentName;
        }
        
        // create the parameter:
        ByReferenceResolveResult brrr = arguments[i] as ByReferenceResolveResult;
        if (brrr != null) {
          list.Add(new DefaultParameter(arguments[i].Type, argumentNames[i], isRef: brrr.IsRef, isOut: brrr.IsOut));
        } else {
          // argument might be a lambda or delegate type, so we have to try to guess the delegate type
          IType type = arguments[i].Type;
          if (type.Kind == TypeKind.Null || type.Kind == TypeKind.Unknown) {
            list.Add(new DefaultParameter(compilation.FindType(KnownTypeCode.Object), argumentNames[i]));
          } else {
            list.Add(new DefaultParameter(type, argumentNames[i]));
          }
        }
      }
      return list;
    }
    
    static string GuessParameterName(ResolveResult rr)
    {
      MemberResolveResult mrr = rr as MemberResolveResult;
      if (mrr != null)
        return mrr.Member.Name;
      
      UnknownMemberResolveResult umrr = rr as UnknownMemberResolveResult;
      if (umrr != null)
        return umrr.MemberName;
      
      MethodGroupResolveResult mgrr = rr as MethodGroupResolveResult;
      if (mgrr != null)
        return mgrr.MethodName;
      
      LocalResolveResult vrr = rr as LocalResolveResult;
      if (vrr != null)
        return MakeParameterName(vrr.Variable.Name);
      
      if (rr.Type.Kind != TypeKind.Unknown && !string.IsNullOrEmpty(rr.Type.Name)) {
        return MakeParameterName(rr.Type.Name);
      } else {
        return "parameter";
      }
    }
    
    static string MakeParameterName(string variableName)
    {
      if (string.IsNullOrEmpty(variableName))
        return "parameter";
      if (variableName.Length > 1 && variableName[0] == '_')
        variableName = variableName.Substring(1);
      return char.ToLower(variableName[0]) + variableName.Substring(1);
    }
    
    OverloadResolution CreateOverloadResolution(ResolveResult[] arguments, string[] argumentNames = null, IType[] typeArguments = null)
    {
      var or = new OverloadResolution(compilation, arguments, argumentNames, typeArguments, conversions);
      or.CheckForOverflow = checkForOverflow;
      return or;
    }
    #endregion
    
    #region ResolveIndexer
    /// <summary>
    /// Resolves an indexer access.
    /// </summary>
    /// <param name="target">Target expression.</param>
    /// <param name="arguments">
    /// Arguments passed to the indexer.
    /// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
    /// </param>
    /// <param name="argumentNames">
    /// The argument names. Pass the null string for positional arguments.
    /// </param>
    /// <returns>ArrayAccessResolveResult, InvocationResolveResult, or ErrorResolveResult</returns>
    public ResolveResult ResolveIndexer(ResolveResult target, ResolveResult[] arguments, string[] argumentNames = null)
    {
      switch (target.Type.Kind) {
        case TypeKind.Dynamic:
          return new DynamicInvocationResolveResult(target, DynamicInvocationType.Indexing, AddArgumentNamesIfNecessary(arguments, argumentNames));
          
        case TypeKind.Array:
        case TypeKind.Pointer:
          // §7.6.6.1 Array access / §18.5.3 Pointer element access
          AdjustArrayAccessArguments(arguments);
          return new ArrayAccessResolveResult(((TypeWithElementType)target.Type).ElementType, target, arguments);
      }
      
      // §7.6.6.2 Indexer access

      MemberLookup lookup = CreateMemberLookup();
      var indexers = lookup.LookupIndexers(target);

      if (arguments.Any(a => a.Type.Kind == TypeKind.Dynamic)) {
        // If we have dynamic arguments, we need to represent the invocation as a dynamic invocation if there is more than one applicable indexer.
        var or2 = CreateOverloadResolution(arguments, argumentNames, null);
        var applicableIndexers = indexers.SelectMany(x => x).Where(m => OverloadResolution.IsApplicable(or2.AddCandidate(m))).ToList();

        if (applicableIndexers.Count > 1) {
          return new DynamicInvocationResolveResult(target, DynamicInvocationType.Indexing, AddArgumentNamesIfNecessary(arguments, argumentNames));
        }
      }

      OverloadResolution or = CreateOverloadResolution(arguments, argumentNames);
      or.AddMethodLists(indexers);
      if (or.BestCandidate != null) {
        return or.CreateResolveResult(target);
      } else {
        return ErrorResult;
      }
    }
    
    /// <summary>
    /// Converts all arguments to int,uint,long or ulong.
    /// </summary>
    void AdjustArrayAccessArguments(ResolveResult[] arguments)
    {
      for (int i = 0; i < arguments.Length; i++) {
        if (!(TryConvert(ref arguments[i], compilation.FindType(KnownTypeCode.Int32)) ||
              TryConvert(ref arguments[i], compilation.FindType(KnownTypeCode.UInt32)) ||
              TryConvert(ref arguments[i], compilation.FindType(KnownTypeCode.Int64)) ||
              TryConvert(ref arguments[i], compilation.FindType(KnownTypeCode.UInt64))))
        {
          // conversion failed
          arguments[i] = Convert(arguments[i], compilation.FindType(KnownTypeCode.Int32), Conversion.None);
        }
      }
    }
    #endregion
    
    #region ResolveObjectCreation
    /// <summary>
    /// Resolves an object creation.
    /// </summary>
    /// <param name="type">Type of the object to create.</param>
    /// <param name="arguments">
    /// Arguments passed to the constructor.
    /// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
    /// </param>
    /// <param name="argumentNames">
    /// The argument names. Pass the null string for positional arguments.
    /// </param>
    /// <param name="allowProtectedAccess">
    /// Whether to allow calling protected constructors.
    /// This should be false except when resolving constructor initializers.
    /// </param>
    /// <param name="initializerStatements">
    /// Statements for Objects/Collections initializer.
    /// <see cref="InvocationResolveResult.InitializerStatements"/>
    /// </param>
    /// <returns>InvocationResolveResult or ErrorResolveResult</returns>
    public ResolveResult ResolveObjectCreation(IType type, ResolveResult[] arguments, string[] argumentNames = null, bool allowProtectedAccess = false, IList<ResolveResult> initializerStatements = null)
    {
      if (type.Kind == TypeKind.Delegate && arguments.Length == 1) {
        ResolveResult input = arguments[0];
        IMethod invoke = input.Type.GetDelegateInvokeMethod();
        if (invoke != null) {
          input = new MethodGroupResolveResult(
            input, invoke.Name,
            methods: new[] { new MethodListWithDeclaringType(invoke.DeclaringType) { invoke } },
            typeArguments: EmptyList<IType>.Instance
          );
        }
        return Convert(input, type);
      }
      OverloadResolution or = CreateOverloadResolution(arguments, argumentNames);
      MemberLookup lookup = CreateMemberLookup();
      var allApplicable = (arguments.Any(a => a.Type.Kind == TypeKind.Dynamic) ? new List<IMethod>() : null);
      foreach (IMethod ctor in type.GetConstructors()) {
        if (lookup.IsAccessible(ctor, allowProtectedAccess)) {
          var orErrors = or.AddCandidate(ctor);
          if (allApplicable != null && OverloadResolution.IsApplicable(orErrors))
            allApplicable.Add(ctor);
        }
        else
          or.AddCandidate(ctor, OverloadResolutionErrors.Inaccessible);
      }

      if (allApplicable != null && allApplicable.Count > 1) {
        // If we have dynamic arguments, we need to represent the invocation as a dynamic invocation if there is more than one applicable constructor.
        return new DynamicInvocationResolveResult(new MethodGroupResolveResult(null, allApplicable[0].Name, new[] { new MethodListWithDeclaringType(type, allApplicable) }, null), DynamicInvocationType.ObjectCreation, AddArgumentNamesIfNecessary(arguments, argumentNames), initializerStatements);
      }

      if (or.BestCandidate != null) {
        return or.CreateResolveResult(null, initializerStatements);
      } else {
        return new ErrorResolveResult(type);
      }
    }
    #endregion
    
    #region ResolveSizeOf
    /// <summary>
    /// Resolves 'sizeof(type)'.
    /// </summary>
    public ResolveResult ResolveSizeOf(IType type)
    {
      IType int32 = compilation.FindType(KnownTypeCode.Int32);
      int? size = null;
      var typeForConstant = (type.Kind == TypeKind.Enum) ? type.GetDefinition().EnumUnderlyingType : type;

      switch (ReflectionHelper.GetTypeCode(typeForConstant)) {
        case TypeCode.Boolean:
        case TypeCode.SByte:
        case TypeCode.Byte:
          size = 1;
          break;
        case TypeCode.Char:
        case TypeCode.Int16:
        case TypeCode.UInt16:
          size = 2;
          break;
        case TypeCode.Int32:
        case TypeCode.UInt32:
        case TypeCode.Single:
          size = 4;
          break;
        case TypeCode.Int64:
        case TypeCode.UInt64:
        case TypeCode.Double:
          size = 8;
          break;
      }
      return new SizeOfResolveResult(int32, type, size);
    }
    #endregion
    
    #region Resolve This/Base Reference
    /// <summary>
    /// Resolves 'this'.
    /// </summary>
    public ResolveResult ResolveThisReference()
    {
      ITypeDefinition t = CurrentTypeDefinition;
      if (t != null) {
        if (t.TypeParameterCount != 0) {
          // Self-parameterize the type
          return new ThisResolveResult(new ParameterizedType(t, t.TypeParameters));
        } else {
          return new ThisResolveResult(t);
        }
      }
      return ErrorResult;
    }
    
    /// <summary>
    /// Resolves 'base'.
    /// </summary>
    public ResolveResult ResolveBaseReference()
    {
      ITypeDefinition t = CurrentTypeDefinition;
      if (t != null) {
        foreach (IType baseType in t.DirectBaseTypes) {
          if (baseType.Kind != TypeKind.Unknown && baseType.Kind != TypeKind.Interface) {
            return new ThisResolveResult(baseType, causesNonVirtualInvocation: true);
          }
        }
      }
      return ErrorResult;
    }
    #endregion
    
    #region ResolveConditional
    /// <summary>
    /// Converts the input to <c>bool</c> using the rules for boolean expressions.
    /// That is, <c>operator true</c> is used if a regular conversion to <c>bool</c> is not possible.
    /// </summary>
    public ResolveResult ResolveCondition(ResolveResult input)
    {
      if (input == null)
        throw new ArgumentNullException("input");
      IType boolean = compilation.FindType(KnownTypeCode.Boolean);
      Conversion c = conversions.ImplicitConversion(input, boolean);
      if (!c.IsValid) {
        var opTrue = input.Type.GetMethods(m => m.IsOperator && m.Name == "op_True").FirstOrDefault();
        if (opTrue != null) {
          c = Conversion.UserDefinedConversion(opTrue, isImplicit: true, conversionBeforeUserDefinedOperator: Conversion.None, conversionAfterUserDefinedOperator: Conversion.None);
        }
      }
      return Convert(input, boolean, c);
    }
    
    /// <summary>
    /// Converts the negated input to <c>bool</c> using the rules for boolean expressions.
    /// Computes <c>!(bool)input</c> if the implicit cast to bool is valid; otherwise
    /// computes <c>input.operator false()</c>.
    /// </summary>
    public ResolveResult ResolveConditionFalse(ResolveResult input)
    {
      if (input == null)
        throw new ArgumentNullException("input");
      IType boolean = compilation.FindType(KnownTypeCode.Boolean);
      Conversion c = conversions.ImplicitConversion(input, boolean);
      if (!c.IsValid) {
        var opFalse = input.Type.GetMethods(m => m.IsOperator && m.Name == "op_False").FirstOrDefault();
        if (opFalse != null) {
          c = Conversion.UserDefinedConversion(opFalse, isImplicit: true, conversionBeforeUserDefinedOperator: Conversion.None, conversionAfterUserDefinedOperator: Conversion.None);
          return Convert(input, boolean, c);
        }
      }
      return ResolveUnaryOperator(UnaryOperatorType.Not, Convert(input, boolean, c));
    }
    
    public ResolveResult ResolveConditional(ResolveResult condition, ResolveResult trueExpression, ResolveResult falseExpression)
    {
      // C# 4.0 spec §7.14: Conditional operator
      
      bool isValid;
      IType resultType;
      if (trueExpression.Type.Kind == TypeKind.Dynamic || falseExpression.Type.Kind == TypeKind.Dynamic) {
        resultType = SpecialType.Dynamic;
        isValid = TryConvert(ref trueExpression, resultType) & TryConvert(ref falseExpression, resultType);
      } else if (HasType(trueExpression) && HasType(falseExpression)) {
        Conversion t2f = conversions.ImplicitConversion(trueExpression, falseExpression.Type);
        Conversion f2t = conversions.ImplicitConversion(falseExpression, trueExpression.Type);
        // The operator is valid:
        // a) if there's a conversion in one direction but not the other
        // b) if there are conversions in both directions, and the types are equivalent
        if (IsBetterConditionalConversion(t2f, f2t)) {
          resultType = falseExpression.Type;
          isValid = true;
          trueExpression = Convert(trueExpression, resultType, t2f);
        } else if (IsBetterConditionalConversion(f2t, t2f)) {
          resultType = trueExpression.Type;
          isValid = true;
          falseExpression = Convert(falseExpression, resultType, f2t);
        } else {
          resultType = trueExpression.Type;
          isValid = trueExpression.Type.Equals(falseExpression.Type);
        }
      } else if (HasType(trueExpression)) {
        resultType = trueExpression.Type;
        isValid = TryConvert(ref falseExpression, resultType);
      } else if (HasType(falseExpression)) {
        resultType = falseExpression.Type;
        isValid = TryConvert(ref trueExpression, resultType);
      } else {
        return ErrorResult;
      }
      condition = ResolveCondition(condition);
      if (isValid) {
        if (condition.IsCompileTimeConstant && trueExpression.IsCompileTimeConstant && falseExpression.IsCompileTimeConstant) {
          bool? val = condition.ConstantValue as bool?;
          if (val == true)
            return trueExpression;
          else if (val == false)
            return falseExpression;
        }
        return new OperatorResolveResult(resultType, System.Linq.Expressions.ExpressionType.Conditional,
                                         condition, trueExpression, falseExpression);
      } else {
        return new ErrorResolveResult(resultType);
      }
    }
    
    bool IsBetterConditionalConversion(Conversion c1, Conversion c2)
    {
      // Valid is better than ImplicitConstantExpressionConversion is better than invalid
      if (!c1.IsValid)
        return false;
      if (c1 != Conversion.ImplicitConstantExpressionConversion && c2 == Conversion.ImplicitConstantExpressionConversion)
        return true;
      return !c2.IsValid;
    }
    
    bool HasType(ResolveResult r)
    {
      return r.Type.Kind != TypeKind.Unknown && r.Type.Kind != TypeKind.Null;
    }
    #endregion
    
    #region ResolvePrimitive
    public ResolveResult ResolvePrimitive(object value)
    {
      if (value == null) {
        return new ResolveResult(SpecialType.NullType);
      } else {
        TypeCode typeCode = Type.GetTypeCode(value.GetType());
        IType type = compilation.FindType(typeCode);
        return new ConstantResolveResult(type, value);
      }
    }
    #endregion
    
    #region ResolveDefaultValue
    public ResolveResult ResolveDefaultValue(IType type)
    {
      return new ConstantResolveResult(type, GetDefaultValue(type));
    }
    
    public static object GetDefaultValue(IType type)
    {
      ITypeDefinition typeDef = type.GetDefinition();
      if (typeDef == null)
        return null;
      if (typeDef.Kind == TypeKind.Enum) {
        typeDef = typeDef.EnumUnderlyingType.GetDefinition();
        if (typeDef == null)
          return null;
      }
      switch (typeDef.KnownTypeCode) {
        case KnownTypeCode.Boolean:
          return false;
        case KnownTypeCode.Char:
          return '\0';
        case KnownTypeCode.SByte:
          return (sbyte)0;
        case KnownTypeCode.Byte:
          return (byte)0;
        case KnownTypeCode.Int16:
          return (short)0;
        case KnownTypeCode.UInt16:
          return (ushort)0;
        case KnownTypeCode.Int32:
          return 0;
        case KnownTypeCode.UInt32:
          return 0U;
        case KnownTypeCode.Int64:
          return 0L;
        case KnownTypeCode.UInt64:
          return 0UL;
        case KnownTypeCode.Single:
          return 0f;
        case KnownTypeCode.Double:
          return 0.0;
        case KnownTypeCode.Decimal:
          return 0m;
        default:
          return null;
      }
    }
    #endregion
    
    #region ResolveArrayCreation
    /// <summary>
    /// Resolves an array creation.
    /// </summary>
    /// <param name="elementType">
    /// The array element type.
    /// Pass null to resolve an implicitly-typed array creation.
    /// </param>
    /// <param name="sizeArguments">
    /// The size arguments.
    /// The length of this array will be used as the number of dimensions of the array type.
    /// Negative values will be treated as errors.
    /// </param>
    /// <param name="initializerElements">
    /// The initializer elements. May be null if no array initializer was specified.
    /// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
    /// </param>
    public ArrayCreateResolveResult ResolveArrayCreation(IType elementType, int[] sizeArguments, ResolveResult[] initializerElements = null)
    {
      ResolveResult[] sizeArgResults = new ResolveResult[sizeArguments.Length];
      for (int i = 0; i < sizeArguments.Length; i++) {
        if (sizeArguments[i] < 0)
          sizeArgResults[i] = ErrorResolveResult.UnknownError;
        else
          sizeArgResults[i] = new ConstantResolveResult(compilation.FindType(KnownTypeCode.Int32), sizeArguments[i]);
      }
      return ResolveArrayCreation(elementType, sizeArgResults, initializerElements);
    }
    
    /// <summary>
    /// Resolves an array creation.
    /// </summary>
    /// <param name="elementType">
    /// The array element type.
    /// Pass null to resolve an implicitly-typed array creation.
    /// </param>
    /// <param name="sizeArguments">
    /// The size arguments.
    /// The length of this array will be used as the number of dimensions of the array type.
    /// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
    /// </param>
    /// <param name="initializerElements">
    /// The initializer elements. May be null if no array initializer was specified.
    /// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
    /// </param>
    public ArrayCreateResolveResult ResolveArrayCreation(IType elementType, ResolveResult[] sizeArguments, ResolveResult[] initializerElements = null)
    {
      int dimensions = sizeArguments.Length;
      if (dimensions == 0)
        throw new ArgumentException("sizeArguments.Length must not be 0");
      if (elementType == null) {
        TypeInference typeInference = new TypeInference(compilation, conversions);
        bool success;
        elementType = typeInference.GetBestCommonType(initializerElements, out success);
      }
      IType arrayType = new ArrayType(compilation, elementType, dimensions);
      
      AdjustArrayAccessArguments(sizeArguments);
      
      if (initializerElements != null) {
        for (int i = 0; i < initializerElements.Length; i++) {
          initializerElements[i] = Convert(initializerElements[i], elementType);
        }
      }
      return new ArrayCreateResolveResult(arrayType, sizeArguments, initializerElements);
    }
    #endregion
    
    public ResolveResult ResolveTypeOf(IType referencedType)
    {
      return new TypeOfResolveResult(compilation.FindType(KnownTypeCode.Type), referencedType);
    }
    
    #region ResolveAssignment
    public ResolveResult ResolveAssignment(AssignmentOperatorType op, ResolveResult lhs, ResolveResult rhs)
    {
      var linqOp = AssignmentExpression.GetLinqNodeType(op, this.CheckForOverflow);
      var bop = AssignmentExpression.GetCorrespondingBinaryOperator(op);
      if (bop == null) {
        return new OperatorResolveResult(lhs.Type, linqOp, lhs, this.Convert(rhs, lhs.Type));
      }
      ResolveResult bopResult = ResolveBinaryOperator(bop.Value, lhs, rhs);
      OperatorResolveResult opResult = bopResult as OperatorResolveResult;
      if (opResult == null || opResult.Operands.Count != 2)
        return bopResult;
      return new OperatorResolveResult(lhs.Type, linqOp, opResult.UserDefinedOperatorMethod, opResult.IsLiftedOperator,
                                       new [] { lhs, opResult.Operands[1] });
    }
    #endregion
  }
}