The only things that are particularly painful about opaque types in C is that you can't easily use stack-based memory to allocate opaque objects. This of course

The only things that are particularly painful about opaque types in C is that you can't easily use stack-based memory to allocate opaque objects. This of course is true for C++ opaque types, but people tend to rely on private fields of concrete types instead of "PIMPL" struct declarations, even though the latter is arguably better for binary compatability and information hiding.