Re: Capy Review

On 6/27/26 02:05, Vinnie Falco via Boost wrote:
> On Fri, Jun 26, 2026 at 3:25 PM Rainer Deyke via Boost <
> [email protected]> wrote:
> 
>> I'm fine with 'co_await foreign_awaitable(awaitable)'
>>
> 
> Let's unpack this. You want:
> 
>      co_await universal_bridge( other_coro() );
> 
> You say you want to call this from inside a Capy coroutine. The desire is
> understandable yet there is an asymmetry here.
> 
> How can universal_bridge() possibly work when other_coro() returns an
> IoAwaitable?
> 
> Answer: it can't.
> 
> universal_bridge() is impossible to implement universally. It is a one-way
> door. Capy can consume the world, but the world can't consume Capy, unless
> the world learns the IoAwaitable protocol. Which means every library needs
> a Capy-specific adapter. Which means N libraries need N adapters. Which
> means it doesn't scale the way you want.

Yes, that's the problem I pointed out.  N libraries, each requiring N - 
1 adapters, where N is constantly growing.  This is not sustainable. 
Capy must either step up as *the* universal coroutine library, or it 
must vanish entirely.  Anything between these two extremes leads to madness.

> The real solution is: everyone agrees on a protocol for propagating
> executor + stop token + allocator. Then one bridge covers everyone. That is
> IoAwaitable. Or, more poignantly:
> 
>      std::io_awaitable

And that's the solution I'm looking for.  But I'm told this is outside 
the scope of Capy, which should only be used for socket-based i/o using 
corosio.

(Although I wish you'd replace the "io" part of the name, because the 
goal is a universal system, not one linked to i/o.  Corosio 
notwithstanding, there is nothing inherent about IoAwaitable that makes 
it more applicable to i/o tasks than any other coroutine task - and if 
there were such a shortcoming, it should be fixed.)


-- 
Rainer Deyke - [email protected]

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