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IEquatable<T> Interface

  • Reference

Definition

Namespace:
System
Assembly:
System.Runtime.dll
Assembly:
mscorlib.dll
Assembly:
netstandard.dll

Defines a generalized method that a value type or class implements to create a type-specific method for determining equality of instances.

generic <typename T>
public interface class IEquatable
public interface IEquatable<T>
type IEquatable<'T> = interface
Public Interface IEquatable(Of T)

Type Parameters

T

The type of objects to compare.

Derived

Examples

See the example for the IEquatable<T>.Equals method.

Remarks

This interface is implemented by types whose values can be equated (for example, the numeric and string classes). A value type or class implements the Equals method to create a type-specific method suitable for determining equality of instances.

Note

The IComparable<T> interface defines the CompareTo method, which determines the sort order of instances of the implementing type. The IEquatable<T> interface defines the Equals method, which determines the equality of instances of the implementing type.

The IEquatable<T> interface is used by generic collection objects such as Dictionary<TKey,TValue>, List<T>, and LinkedList<T> when testing for equality in such methods as Contains, IndexOf, LastIndexOf, and Remove. It should be implemented for any object that might be stored in a generic collection.

Notes to Implementers

Replace the type parameter of the IEquatable<T> interface with the type that is implementing this interface.

If you implement IEquatable<T>, you should also override the base class implementations of Equals(Object) and GetHashCode() so that their behavior is consistent with that of the Equals(T) method. If you do override Equals(Object), your overridden implementation is also called in calls to the static Equals(System.Object, System.Object) method on your class. In addition, you should overload the op_Equality and op_Inequality operators. This ensures that all tests for equality return consistent results.

For information on overriding Equals(Object), see Equals(Object).

For a value type, you should always implement IEquatable<T> and override Equals(Object) for better performance. Equals(Object) boxes value types and relies on reflection to compare two values for equality. Both your implementation of Equals(T) and your override of Equals(Object) should return consistent results.

If you implement IEquatable<T>, you should also implement IComparable<T> if instances of your type can be ordered or sorted. If your type implements IComparable<T>, you almost always also implement IEquatable<T>.

Note that there are some designs where a type supports an order relation, but equality may be distinct from an ordering relation. Consider a Person class where you sort alphabetically. Two people with the same name sort the same, but are not the same person.

Methods

Equals(T)

Indicates whether the current object is equal to another object of the same type.

Applies to

See also