source: branches/2994-AutoDiffForIntervals/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory-5.5.0/Utils/ImmutableStack.cs

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// 
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// 
// 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.Text;

namespace ICSharpCode.NRefactory.Utils
{
  /// <summary>
  /// An immutable stack.
  /// 
  /// Using 'foreach' on the stack will return the items from top to bottom (in the order they would be popped).
  /// </summary>
  [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1710:IdentifiersShouldHaveCorrectSuffix")]
  [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1711:IdentifiersShouldNotHaveIncorrectSuffix")]
  [Serializable]
  public sealed class ImmutableStack<T> : IEnumerable<T>
  {
    /// <summary>
    /// Gets the empty stack instance.
    /// </summary>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Security", "CA2104:DoNotDeclareReadOnlyMutableReferenceTypes", Justification = "ImmutableStack is immutable")]
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1000:DoNotDeclareStaticMembersOnGenericTypes")]
    public static readonly ImmutableStack<T> Empty = new ImmutableStack<T>();
    
    readonly T value;
    readonly ImmutableStack<T> next;
    
    private ImmutableStack()
    {
    }
    
    private ImmutableStack(T value, ImmutableStack<T> next)
    {
      this.value = value;
      this.next = next;
    }
    
    /// <summary>
    /// Pushes an item on the stack. This does not modify the stack itself, but returns a new
    /// one with the value pushed.
    /// </summary>
    public ImmutableStack<T> Push(T item)
    {
      return new ImmutableStack<T>(item, this);
    }
    
    /// <summary>
    /// Gets the item on the top of the stack.
    /// </summary>
    /// <exception cref="InvalidOperationException">The stack is empty.</exception>
    public T Peek()
    {
      if (IsEmpty)
        throw new InvalidOperationException("Operation not valid on empty stack.");
      return value;
    }
    
    /// <summary>
    /// Gets the item on the top of the stack.
    /// Returns <c>default(T)</c> if the stack is empty.
    /// </summary>
    public T PeekOrDefault()
    {
      return value;
    }
    
    /// <summary>
    /// Gets the stack with the top item removed.
    /// </summary>
    /// <exception cref="InvalidOperationException">The stack is empty.</exception>
    public ImmutableStack<T> Pop()
    {
      if (IsEmpty)
        throw new InvalidOperationException("Operation not valid on empty stack.");
      return next;
    }
    
    /// <summary>
    /// Gets if this stack is empty.
    /// </summary>
    public bool IsEmpty {
      get { return next == null; }
    }
    
    /// <summary>
    /// Gets an enumerator that iterates through the stack top-to-bottom.
    /// </summary>
    public IEnumerator<T> GetEnumerator()
    {
      ImmutableStack<T> t = this;
      while (!t.IsEmpty) {
        yield return t.value;
        t = t.next;
      }
    }
    
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
      return this.GetEnumerator();
    }
    
    /// <inheritdoc/>
    public override string ToString()
    {
      StringBuilder b = new StringBuilder("[Stack");
      foreach (T val in this) {
        b.Append(' ');
        b.Append(val);
      }
      b.Append(']');
      return b.ToString();
    }
  }
}