source: branches/2522_RefactorPluginInfrastructure/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory-5.5.0/Role.cs

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// 
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// 
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using System;
using System.Threading;

namespace ICSharpCode.NRefactory
{
  /// <summary>
  /// Represents the role a node plays within its parent.
  /// </summary>
  public abstract class Role
  {
    public const int RoleIndexBits = 9;
    
    static readonly Role[] roles = new Role[1 << RoleIndexBits];
    static int nextRoleIndex = 0;
    
    readonly uint index;
    
    [CLSCompliant(false)]
    public uint Index {
      get { return index; }
    }
    
    // don't allow NRefactory consumers to derive from Role
    internal Role()
    {
      this.index = (uint)Interlocked.Increment(ref nextRoleIndex);
      if (this.index >= roles.Length)
        throw new InvalidOperationException("Too many roles");
      roles[this.index] = this;
    }
    
    /// <summary>
    /// Gets whether the specified node is valid in this role.
    /// </summary>
    public abstract bool IsValid(object node);
    
    /// <summary>
    /// Gets the role with the specified index.
    /// </summary>
    [CLSCompliant(false)]
    public static Role GetByIndex(uint index)
    {
      return roles[index];
    }
  }
  
  /// <summary>
  /// Represents the role a node plays within its parent.
  /// All nodes with this role have type T.
  /// </summary>
  public class Role<T> : Role where T : class
  {
    readonly string name; // helps with debugging the AST
    readonly T nullObject;
    
    /// <summary>
    /// Gets the null object used when there's no node with this role.
    /// Not every role has a null object; this property returns null for roles without a null object.
    /// </summary>
    /// <remarks>
    /// Roles used for non-collections should always have a null object, so that no AST property returns null.
    /// However, if a role used for collections only, it may leave out the null object.
    /// </remarks>
    public T NullObject {
      get { return nullObject; }
    }
    
    public override bool IsValid(object node)
    {
      return node is T;
    }
    
    public Role(string name)
    {
      if (name == null)
        throw new ArgumentNullException("name");
      this.name = name;
    }
    
    public Role(string name, T nullObject)
    {
      if (name == null)
        throw new ArgumentNullException("name");
      if (nullObject == null)
        throw new ArgumentNullException ("nullObject");
      this.nullObject = nullObject;
      this.name = name;
    }
    
    public override string ToString()
    {
      return name;
    }
  }
}