[cfe-dev] C++1z invocation_traits

[Richard Smith]

On Tue, Jan 27, 2015 at 11:34 AM, Marshall Clow <mclow.lists at gmail.com>
wrote:

>
> On Jan 27, 2015, at 12:03 AM, Ben Pope <benpope81 at gmail.com> wrote:
>
> On Tuesday, January 27, 2015 03:59 PM, Ben Pope wrote:
>
> On Tuesday, January 27, 2015 02:28 PM, Michael Haidl wrote:
>
> Hi all,
>
> I am curious about the proposed invocation traits
> (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3866.html) and
> life would be a lot easier if they would make it into the next C++
> standard (at least for me). However 201z is far away and I was wondering
> if someone is already working on this in clang. If not can someone
> direct me to the right spot in clang where such a feature would be in
> the right place?
>
>
> I'm not sure what happened, they appear to have made it to N3908, then
> to N4023, then to N4081 but they don't appear in N4270.
>
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/
>
>
> They're hiding here:
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4335.html
>
>
> In other words, they’ll appear in libc++.
> [ We’re trying to get a full LFTS implementation in there, but it’s not
> all there yet ]
>

We should figure out what intrinsics you guys want in order to support
this. I believe it's straightforward to implement invocation_type in terms
of raw_invocation_type in the library, so I think providing simply a
__raw_invocation_type(Fn, Arg1, Arg2, ...) would work?

Looking at N4335 now, I'm a little concerned that we may be standardizing a
bad interface; we don't support using raw_invocation_type<F(Args...)> if F
is a function type, because that would create a function type whose return
type is a function type, which is ill-formed.
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