Pitfalls - StephenCleary/Comparers GitHub Wiki

The one major pitfall in the Comparers library is that every comparer implementation assumes that it has a GetHashCode implementation available.

The core comparer implementations (Compare<T>.Default(), Compare<T>.Null(), and types derived from ComparableBase<T>) do provide GetHashCode. Every comparer extension provides GetHashCode if their source comparer(s) provide GetHashCode.

The pitfall comes in when a comparer extension is used on a "bare bones" comparer that does not provide GetHashCode. This happens in two situations:

• A custom IComparer<T> implementation is used with a comparer extension from the Comparers library.
• An AnonymousComparer<T> instance is used without defining the GetHashCode delegate.

In this case, the resulting comparer will function correctly as a comparer, but it will fail at runtime if it ever attempts to execute GetHashCode.