Mangling isn't magic. You have a type T, and a struct U which contains a T. A function takes a U by reference, and therefore will be mangled with U. However

Mangling isn't magic. You have a type T, and a struct U which contains a T. A function takes a U by reference, and therefore will be mangled with U. However say that function was built with a different version of T than the caller. This doesn't affect mangling. Things silently work even though they break. This is a basic pitfall of working with any system that allows linking of binaries. The setup only works so long as you guarantee that all entities with the same name are indeed the same thing. This is the One Definition Rule.