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ReferenceEqualityComparer.cs
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ReferenceEqualityComparer.cs
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//Copyright 2010 Microsoft Corporation
//
//Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
//You may obtain a copy of the License at
//
//http://www.apache.org/licenses/LICENSE-2.0
//
//Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an
//"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//See the License for the specific language governing permissions and limitations under the License.
#if ASTORIA_CLIENT
namespace System.Data.Services.Client
#else
namespace System.Data.Services
#endif
{
#region Namespaces.
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq.Expressions;
using System.Text;
using System.Collections;
#endregion Namespaces.
internal class ReferenceEqualityComparer : IEqualityComparer
{
#region Private fields.
#if NON_GENERIC_AVAILABLE
private static ReferenceEqualityComparer nonGenericInstance;
#endif
#endregion Private fields.
#region Constructors.
protected ReferenceEqualityComparer()
{
}
#endregion Constructors.
#region Properties.
bool IEqualityComparer.Equals(object x, object y)
{
return object.ReferenceEquals(x, y);
}
int IEqualityComparer.GetHashCode(object obj)
{
if (obj == null)
{
return 0;
}
return obj.GetHashCode();
}
#if NON_GENERIC_AVAILABLE
internal ReferenceEqualityComparer NonGenericInstance
{
get
{
if (nonGenericInstance == null)
{
ReferenceEqualityComparer comparer = new ReferenceEqualityComparer();
System.Threading.Interlocked.CompareExchange(ref nonGenericInstance, comparer, null);
}
return nonGenericInstance;
}
}
#endif
#endregion Properties.
}
internal sealed class ReferenceEqualityComparer<T> : ReferenceEqualityComparer, IEqualityComparer<T>
{
#region Private fields.
private static ReferenceEqualityComparer<T> instance;
#endregion Private fields.
#region Constructors.
private ReferenceEqualityComparer() : base()
{
}
#endregion Constructors.
#region Properties.
internal static ReferenceEqualityComparer<T> Instance
{
get
{
if (instance == null)
{
Debug.Assert(!typeof(T).IsValueType, "!typeof(T).IsValueType -- can't use reference equality in a meaningful way with value types");
ReferenceEqualityComparer<T> newInstance = new ReferenceEqualityComparer<T>();
System.Threading.Interlocked.CompareExchange(ref instance, newInstance, null);
}
return instance;
}
}
#endregion Properties.
#region Methods.
public bool Equals(T x, T y)
{
return object.ReferenceEquals(x, y);
}
public int GetHashCode(T obj)
{
if (obj == null)
{
return 0;
}
return obj.GetHashCode();
}
#endregion Methods.
}
}