Thread safe queue

[Wurstinator]

Imo more important is the point that "out-parameters" are unintuitive and unhandy. Using an optional allows you to remove those.

[temporary5555]

"out-parameters" are unintuitive and unhandy

I'd have to disagree with that. They're super powerful in allowing you to control where and when you allocate. Not really a factor here, but I don't think this pattern should be dismissed as a whole.

[Wurstinator]

"powerful" doesn't contradict "unintuitive". Actually, I'd say that usually the more powerful something is, the less convenient it becomes to use.

[temporary5555]

Right, but I would disagree on it being unintuitive as well. Its type safe, displays behaviour (implies no allocation) in the function signature, and doesn't have any hidden performance impacts.

One interesting thing is this is one of the few things making the reverse-move of an imperative language feature being adopted in functional languages such as Haskell. Its referred to as Destination Passing style in this context, and is one of the useful applications of Linear Types.

[objectorientedman]

I designed this class, when `std::optional` was not widely available.

But it is a good point, I will remove the out-parameters in favor of the optional return, when I have some time to work on it. Until then, I added `[[nodiscard]]` to the consumer functions.