Question

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>?

Answer 1

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.