Question

Regarding to the requirement for C++ stl container element, the standard says: the element type should be CopyConstructible, and there is a table for CopyConstructible requirements. Also by various books (Josuttis, etc.), the generated copy should be “equivalent to” the source.

I think I need some clarity here. What is exactly “equivalent to”? Also I am a bit confused with the relation between the “CopyConstructible” and the “deep/shallow copy”. In general, a copy constructor is either shallow copy or deep copy. So which one applies to the “CopyConstructible”, and which does not?

Thanks for any comments!

Answer 1

Deep or shallow copy both work. For instance, shared_ptr always does a shallow copy (with some extra reference counting stuff), and you can use them in containers just fine. It depends on the semantics of copy-operation.

Equivalent means your program should not depend on whether it works with the original or with the copy.