Re: [boost] [boost.asynch] another generator query

19 Aug 2023

      sob., 19 sie 2023 o 03:37 Klemens Morgenstern <
klemensdavidmorgenstern@gmail.com> napisał(a):
...
On Sat, Aug 19, 2023 at 4:41 AM Andrzej Krzemienski via Boost
 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::generatorstd::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::generatorstd::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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