Why does std::reverse require bidirectional iterators?

Question

Why does std::reverse(c.begin(), c.end()) require that the underlying container c provides bidirectional iterator ?

De-facto this would mean (multi-) map , (multi-) set , but those can not reversed, of course, because they are ordered. The only other bi-dir container is list but that one has its own member function .reverse() .

This means that one can apply std::reverse on array , vector and deque which are random-access .

So, why not be "honest" and say: random-access is required, or use the member function?

Answer 1

You don't even need to go user-defined iterators, you provide an answer in your own question.

The only other bi-dir container is list but that one has its own member function .reverse() .

That member function, however, reverses the whole list. std::reverse allows only part of the list to be reversed, by passing other iterators than list.begin() and list.end() .

Answer 2

Doing this would be unnecessarily restrictive for user-defined iterators or cointainers using bidireactional iterators. And since random access is not necessary, it shouldn't be required.