Re: [boost] Noexcept

Subject: Re: [boost] Noexcept
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2017-06-13 22:05:17

On Tue, Jun 13, 2017 at 1:01 PM, Bjorn Reese via Boost <
boost_at_[hidden]> wrote:

> On 06/13/2017 12:38 AM, Emil Dotchevski via Boost wrote:
>
> I'll spell it out: Noexcept + optional<> ≈ Outcome
>>
>
> That approximation only holds for function-calling scenarios. As I
> pointed out in my review, there are other use cases for Outcome.
> Noexcept is a bad match for these use cases, because it transports
> errors "out-of-band" like errno.
>
> One use case is to pass a value-or-error between threads. We already
> have one outcome-like feature for this: promise-future. If we want to
> use a different mechanism to pass the value-or-error between threads,
> then Outcome offers a natural solution.
>
> Another use case is to pass a value-or-error via a queue. The queue
> may contain several outstanding errors. In the case of Outcome, we
> simply push the value-or-error directly to the queue.

Yes, though I consider this a separate issue. One is, what's the best way
to transport errors across error-neutral functions within a single thread,
the other is what to do when, somewhere way up the stack, we get a
successful value or an error. At that point it's trivial to build a
variant<T,std::exception_ptr> or equivalent, you don't need a lib for that.