I think there is exactly one equivalence class of instances of std::monostate, whereas there are exactly zero equivalence classes of instances of void. In cate

I think there is exactly one equivalence class of instances of std::monostate, whereas there are exactly zero equivalence classes of instances of void. In category theory terms, I believe void is the initial type (there is exactly one morphism from void to any other type), whereas monostate is the terminal type (there is exactly one morphism from any other type to monotype).