Re: [boost] [WG21 mailing] N4453 Resumable expressions

Subject: Re: [boost] [WG21 mailing] N4453 Resumable expressions
From: TONGARI J (tongari95_at_[hidden])
Date: 2015-04-15 10:55:55

2015-04-15 21:27 GMT+08:00 Niall Douglas <s_sourceforge_at_[hidden]>:

> I'm finding Chris' paper on resumable expressions instead of compiler
> magic created resumable functions awfully compelling:
>
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4453.pdf
>
> I essentially proposed the same with my functionally composed
> constexpr basic_future design some months ago.
>
> Would anyone else like to comment on this library based instead of
> compiler based resumable execution? I'm not against some compiler
> support for resumable execution, but I am finding the await based
> proposal highly problematic, and Chris does an excellent job in
> summarising my own thoughts on what's wrong with it.
>

IIUC, this proposal requires more compiler magic and is definitely compiler
based.

Await/yield from the "Resumable Functions" proposal is not that mysterious
as one may think, at least I can emulate it in some degree using
preprocessor: (https://github.com/jamboree/co2)

The main point of this proposal is the implicit propagation of the
resumability, that is, if a function calls a resumable function, then the
function itself becomes a resumable function, which makes the existing
template-based algorithms also usable to resumable functions.

A major benefit of this approach is that it provides a unified syntax for
both stackful and stackless coroutine, and IMHO is better than the approach
proposed in N4398.

In general, I like the idea of N4453 and would love to see a working
language implementation.

That said, I do have some questions, for example, it's not clear to me that
whether a ctor/dtor could be a resumable function or not, and there may be
some other issues that I can't foresee without playing with it.