Question

I tried to find out how C# goes about comparing objects in a HashSet for equality.

I couldn’t find anything here: http://msdn.microsoft.com/en-us/library/bb359438.aspx

Only when I came to stackoverflow, I read that it uses the Equals() and maybe getHashCode()

I was planning to implement both methods anyways, but my question is:

What would you do to find out how HashSet actually compares objects?

Answer 1

It compares objects for equality using Equals. It determines which bucket to place them in using GetHashCode.

More generically, HashSet uses the IEqualityComparer<T> passed in to its constructor to do both. If none is specified, it uses EqualityComparer<T>.Default which calls the object’s GetHashCode() and IEquatable<T>.Equals() method (or object.Equals() if the type doesn’t implement IEquatable<T>).