Why don't the standard C++ container adaptors provide a clear function?

Question

Does anyone know why std::queue, std::stack, and std::priority_queue don't provide a clear() member function? I have to fake one like this:

std::queue<int> q; // time passes... q = std::queue<int>();  // equivalent to clear() 

IIRC, clear() is provided by everything that could serve as the underlying container. Is there a good reason to not have the container adaptors provide it?

Answer 1

Well, I think this is because clear was not considered a valid operation on a queue, a priority_queue or a stack (by the way, deque is not and adaptor but a container).

The only reason to use the container adaptor queue instead of the container deque is to make it clear that you are performing only queue operations, and no other operations. (from the sgi page on queue)

So when using a queue, all you can do is push/pop elements; clearing the queue can be seen as a violation of the FIFO concept. Consequently, if you need to clear your queue, maybe it's not really a queue and you should better use a deque.

However, this conception of things is a little narrow-minded, and I think clearing the queue as you do is fair enough.

Answer 2

Deque has clear(). See, e.g., http://www.cplusplus.com/reference/stl/deque/clear.html.

However, queue does not. But why would you choose queue over deque, anyway?

The only reason to use the container adaptor queue instead of the container deque is to make it clear that you are performing only queue operations, and no other operations.

(http://www.sgi.com/tech/stl/queue.html)

So I guess clear() is not a queue operation, then.