Re: Capy: Request for endorsements

On Fri, Feb 20, 2026 at 4:32 AM Amlal El Mahrouss via Boost <
[email protected]> wrote:

> I also have a question about the following snippet at:
> https://github.com/cppalliance/capy/blob/develop/example/asio/use_capy_example.cpp#L118C70-L119C1
>
> We can see at line 119:
>
> ```cpp
> capy::run_async(ctx.get_executor())(run_example(client, server));
> ```
>
> It's elegant, but maybe we could also benefit from this syntax as well:
>
> ```cpp
> auto& exec{ctx.get_executor()};
> exec.run_async(run_example(client, server));
> ```
>

So, if I understand you correctly then you are asking for the Executor
concept to have additional members:

    unspecified run_async( IoRunnable auto&& );

This is problematic for a few reasons explained P4003[1]

1.  An Executor is a low-level primitive. It only specifies how a coroutine
is resumed. A launch function is something different: a high level
construct responsible for creating the environment in which a coroutine
runs, and specifying behavior when the coroutine performs its final
suspend. run_async falls in the latter category.

2. The one-call syntax you propose suffers from the allocator timing
problem described in P4007 Senders and Coroutines [2]. The coroutine frame
would be created before the allocator has the chance to propagate.

3. `run_async` is just one example of a launch function: a function which
begins a new coroutine chain of execution either from a regular function
(such as main) or a coroutine. The set of launch functions is open, as
users can (and will) define their own. Here is one such example:

https://github.com/cppalliance/corosio/blob/0cb2c0096ca2cf8f7c1f1617cb04c19120dd4f12/include/boost/corosio/tcp_server.hpp#L500

It makes sense to keep the Executor concept as a low-level narrow
abstraction, and partition the launch functions into a higher level
algorithmic set.

Thanks

[1] https://wg21.link/p4003 IoAwaitables: A Coroutines-Only Framework

[2] https://wg21.link/p4007 Senders and Coroutines

P.S. I suppose its pointless asking for the copyright discussion to be
moved to a separate thread :)
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