//----------------------------------------------------------------------------------------
//
// <copyright file="WeakReferenceKey.cs" company="Microsoft">
//    Copyright (C) Microsoft Corporation.  All rights reserved.
// </copyright>
//
// Description:
//  This file defines a class that holds a weak reference to an object.  It preserves the hashcode 
//  of the object and is intended to be used as a key in hashtables or dictionaries.
//
//--------------------------------------------------------------------------------------
 
 
using System;
using MS.Internal;
 
namespace MS.Internal.Utility
{
	/// <summary>
    /// Helper class that allows using a weak reference to an item as a key in a hash table.
    /// </summary>
    internal class WeakReferenceKey<T>
    {
        public WeakReferenceKey(T item)
        {
            Invariant.Assert(item != null);
 
            _item = new WeakReference(item);
            _hashCode = item.GetHashCode();
        }
 
        public T Item
        {
            get { return (T)_item.Target; }
        }
 
        public override bool Equals(object o)
        {
            if (o == this)
                return true;
 
            WeakReferenceKey<T> key = o as WeakReferenceKey<T>;
            if (key != null)
            {
                T item = this.Item;
                
                if (item == null)
                    return false;   // a stale key matches nothing (except itself)
 
                return this._hashCode == key._hashCode &&
                        Object.Equals(item, key.Item);
            }
 
            return false; 
        }
 
        public override int GetHashCode()
        {
            return _hashCode;
        }
 
        private WeakReference _item;
        private int _hashCode;
    }
}