>The unbound version even does a proper virtual dispatch for you--in C++ you can break class invariants by skipping a virtual dispatch by using a member pointer

>The unbound version even does a proper virtual dispatch for you--in C++ you can break class invariants by skipping a virtual dispatch by using a member pointer. This is not true, the C++ version does the proper virtual dispatch. >I understand C++'s intention, but it's doing no one any favors here and makes it really hard to build proper abstractions. std::function is a perfectly fine abstraction built on-top of the lower level primitives if you don't care about always paying a performance penalty. As someone who writes performance sensitive code, I do care so I try to avoid that penalty. >std::function is considerably more heavyweight (and according to this https://stackoverflow.com/questions/13503511/sizeof-of-stdfu https://stackoverflow.com/questions/13503511/sizeof-of-stdfu... might be arbitrarily large); Of course std::function can allocate arbitrarily large amounts of memory, so can Virgil's implementation. The sizeof(std::function) is always fixed, but because it can capture arbitrarily functions which themselves can carry arbitrarily large state, then so too must std::function also have the potential to allocate arbitrarily large amounts of memory. In C++ people avoid std::function because as you said it's slow, and people tend to not use C++ for programs that can be slow, this goes back to the principle of not having to pay for what you don't use. In other languages you don't get that choice, you basically are required to pay the worst case cost even if you never use it.