dotnet/corefx — pull request #223 by AArnott (2014-12-10 23:42:33+00:00)
Title: Avoid boxing ImmutableHashSet<T>.Enumerator

This introduces a pattern that can be applied anywhere to conveniently avoid boxing one's own Enumerator struct without duplicating the body of foreach loops everywhere.

Fixes #211

If folks like this, I can add a commit that applies the pattern to all the other immutable collection types.