Bjarne Stroustrup on structs vs. classes

This article is really dedicated to C++ but have some really useful insight on when to use structs instead of classes (in C# for example). Usually, this discussion revolves around where structs and classes are instantiated (the stack and the heap) and performance in general, but here Bjarne defines and exemplifies invariants and in so doing proposes a very nice object-oriented way of choosing one or another. One more design pattern to my bag.