CODEWITHSUNDEEP
c#
Chris Dargis
Chris Dargis

Reputation: 6043

Will Dictionary<TKey, TValue> use TKey.Equals and TKey.GetHashCode?

I have implemented a Dictionary as follows:

Dictionary<ErrorHashKey, ErrorRow> dictionary;

I have defined Equals() and GetHashCode() in the ErrorHashKey class. I am currently writing up some documentation for the project, and came accross this from the IEqualityComparer Interface doc:

Dictionary requires an equality implementation to determine whether keys are equal. You can specify an implementation of the IEqualityComparer generic interface by using a constructor that accepts a comparer parameter; if you do not specify an implementation, the default generic equality comparer EqualityComparer.Default is used. If type TKey implements the System.IEquatable generic interface, the default equality comparer uses that implementation.

I am not doing anything that the documentation specifies (or at least I don't think I am). I do not pass a comparer in the constructor parameter nor do I create an EqualityComparer.Default comparer.

Is the System.IEquatable<T> generic interface automatically implemented in every class created? Should I be defining an implementation of IEqualityComparer<T>?

Upvotes: 4

Views: 379

Answers (2)

Amiram Korach
Amiram Korach

Reputation: 13286

The answer id in your question:

if you do not specify an implementation, the default generic equality comparer EqualityComparer.Default is used

EqualityComparer.Default is using the Equals method if you're not implementing IEquatable.

The Default property checks whether type T implements the System.IEquatable interface and, if so, returns an EqualityComparer that uses that implementation. Otherwise, it returns an EqualityComparer that uses the overrides of Object.Equals and Object.GetHashCode provided by T.

Source: http://msdn.microsoft.com/en-us/library/ms224763(v=vs.110).aspx

Upvotes: 1

Tim S.
Tim S.

Reputation: 56536

The default comparer will call object.Equals or object.GetHashCode (your overridden methods) if IEquatable<T> is not implemented. This is documented at the documentation for EqualityComparer<T>.Default. You don't need to do anything extra, and no, IEquatable<T> is not automatically implemented in your class.

Upvotes: 7

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