Re: [boost] [container] Proposal for ring queues

On 2020-05-22 14:32, Mathias Gaunard wrote:

On Fri, 22 May 2020, 11:24 Andrey Semashev via Boost, mailto:boost@lists.boost.org> wrote:

circular_buffer is not a queue. The important difference is that it overwrites older elements as you keep pushing new elements into it.

That's just the behaviour when you run out of capacity. Nothing prevents you from checking you're out of capacity and have different behaviour instead.

Yes, that is a possible workaround, but definitely not the intended use of a circular buffer.

As I said, the main advantage is avoiding dynamic memory allocations

You cannot avoid memory allocations if your queue is unbounded.

If pre-allocation of some size is a concern you can just use an adequate allocator.

One allocation might not be a problem, and small_ring_queue allows to avoid even that, if the optimal capacity is known at compile time. However, std::deque continues to dynamically allocate chunks as you push and pop elements, even if the average number of enqueued elements stays the same. This is avoided by ring queues.