String Buffer

using System;

namespace System.Utilities
{
  /// <summary>
  /// Builds a string. Unlike StringBuilder this class lets you reuse it's internal buffer.
  /// </summary>
  internal class StringBuffer
  {
    private char[] _buffer;
    private int _position;

    private static readonly char[] _emptyBuffer = new char[0];

    public int Position
    {
      get { return _position; }
      set { _position = value; }
    }

    public StringBuffer()
    {
      _buffer = _emptyBuffer;
    }

    public StringBuffer(int initalSize)
    {
      _buffer = new char[initalSize];
    }

    public void Append(char value)
    {
      // test if the buffer array is large enough to take the value
      if (_position + 1 > _buffer.Length)
      {
        EnsureSize(1);
      }

      // set value and increment poisition
      _buffer[_position++] = value;
    }

    public void Clear()
    {
      _buffer = _emptyBuffer;
      _position = 0;
    }

    private void EnsureSize(int appendLength)
    {
      char[] newBuffer = new char[(_position + appendLength) * 2];

      Array.Copy(_buffer, newBuffer, _position);

      _buffer = newBuffer;
    }

    public override string ToString()
    {
      return ToString(0, _position);
    }

    public string ToString(int start, int length)
    {
      // TODO: validation
      return new string(_buffer, start, length);
    }
  }
}