Re: [boost.asynch] another generator query

From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2023-08-19 08:13:22

sob., 19 sie 2023 o 03:37 Klemens Morgenstern <
klemensdavidmorgenstern_at_[hidden]> napisał(a):

> On Sat, Aug 19, 2023 at 4:41 AM Andrzej Krzemienski via Boost
> <boost_at_[hidden]> wrote:
> >
> > Hi Klemens,
> > I have another question regarding the generator.
> > I think the initial examples in the dcs for `generator` are too
> simplistic,
> > because the caller seems to already know how many times it is allowed to
> > co_await on the Awaitable. I tried it with a loop, where I use the
> explicit
> > conversion to bool to check when to break the iteration:
> >
> > ```
> > async::generator<std::string> worker(int limit)
> > {
> >     for (int i = 0; i < limit; ++i) {
> >         co_yield std::format("--{}--", i);
> >     }
> > }
>
> This is missing a co_return at the end. Because the generators are
> async I can't look ahead like std::generator. So this should be
>
> async::generator<std::string> worker(int limit)
> {
>     for (int i = 0; i < limit; ++i) {
>         if (i == (limit - 1))
>             co_return std::format("--{}--", i);
>         co_yield std::format("--{}--", i);
>     }
> }
>

Ok, so I am hearing that "async::generator is async and std::generator is
sync". I do not know what that means exactly. I guess I do not know what it
means for a generator to be async.
Second, I report a concern that Boost.async reuses a name 'generator' that
is already used in STD, in a similar context, but with a different meaning:
different enough that the intuition from std::generator cannot be applied
to async::generator.
Third, I recommend devoting more space to `generator` in the documentation:
(1) the initial example should be more real-life. For instance,
demonstrating how `operator bool` is used correctly. (2) the tutorial
section should have one example containing `generator`. Currently there is
none and this seems to indicate that generator is a second-class type in
this library. You mentioned the state machine in another email. Maybe this
would be a good fit.

It looks like I am just dumping requests. I am unable to offer help with
it, as I genuinely cannot build any intuition around `async::generator`.

Regards,
&rzej;

>
> Or you return and empty string and handle it on the consumer side as an
> EOI.
>
> >
> > async::main co_main(int argc, char* argv[])
> > {
> >     try {
> >         auto w = worker(3);
> >         while (w) {
> >             std::cout << co_await w << std::endl;
> >         }
> >     }
> >     catch (std::exception const& e) {
> >         std::cout << "ERR: " << e.what() << std::endl;
> >     }
> > }
> > ```
> >
> > But I am surprised that this construct ends with throwing an exception.
> > Am I doing something  wrong?
> >
> > Regards,
> > &rzej;
> >
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