EqualityComparer<T> Class


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Provides a base class for implementations of the IEqualityComparer<T> generic interface.

Namespace:   System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)


generic<typename T>
public ref class EqualityComparer abstract : IEqualityComparer, 

Type Parameters


The type of objects to compare.


Initializes a new instance of the EqualityComparer<T> class.


Returns a default equality comparer for the type specified by the generic argument.

System_CAPS_pubmethodEquals(T, T)

When overridden in a derived class, determines whether two objects of type T are equal.


Determines whether the specified object is equal to the current object.(Inherited from Object.)


Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)


Serves as the default hash function. (Inherited from Object.)


When overridden in a derived class, serves as a hash function for the specified object for hashing algorithms and data structures, such as a hash table.


Gets the Type of the current instance.(Inherited from Object.)


Creates a shallow copy of the current Object.(Inherited from Object.)


Returns a string that represents the current object.(Inherited from Object.)

System_CAPS_pubinterfaceSystem_CAPS_privmethodIEqualityComparer::Equals(Object^, Object^)

Determines whether the specified objects are equal.


Returns a hash code for the specified object.

Derive from this class to provide a custom implementation of the IEqualityComparer<T> generic interface for use with collection classes such as the Dictionary<TKey, TValue> generic class, or with methods such as List<T>::Sort.

The Default property checks whether type T implements the System::IEquatable<T> generic interface and, if so, returns an EqualityComparer<T> that invokes the implementation of the IEquatable<T>::Equals method. Otherwise, it returns an EqualityComparer<T>, as provided by T.

We recommend that you derive from the EqualityComparer<T> class instead of implementing the IEqualityComparer<T> interface, because the EqualityComparer<T> class tests for equality using the IEquatable<T>::Equals method instead of the Object::Equals method. This is consistent with the Contains, IndexOf, LastIndexOf, and Remove methods of the Dictionary<TKey, TValue> class and other generic collections.

The following example creates a dictionary collection of objects of type Box with an equality comparer. Two boxes are considered equal if their dimensions are the same. It then adds the boxes to the collection.

The dictionary is recreated with an equality comparer that defines equality in a different way: Two boxes are considered equal if their volumes are the same.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1

Any public static ( Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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