[c++-concepts] Check function concept definitions
Mon Sep 29 17:50:00 GMT 2014
On 2014-09-29 18:32, Jason Merrill wrote:
> On 09/29/2014 11:46 AM, Andrew Sutton wrote:
>> The main reason for the restriction is that concept definitions are
>> normalized into a single constraint-expression. And it's not obvious
>> how things like using declarations and static-assertions should be
>> interpreted within the constraint language.
> A using-declaration just affects name lookup. They and
> typedefs/aliases can help to make the return statement easier to write.
>> That said, having a static_assert inside a concept kind of defeats the
>> purpose since it triggers a diagnostic when its condition isn't
>> satisfied. That's not very SFINAE friendly :)
> True. It might still be useful if for some reason testing a concept
> for a certain class of types indicates an error somewhere else. And
> people are likely to try it, as indicated by the bug report. :)
>> Maybe the restriction can relaxed when we consider the TS for
>> adoption in 17.
> I suppose, but I'd prefer not to wait that long. I guess we can talk
> about it on the call today.
Since I sent that sample code with the static_assert inside the concept,
let me add that I wanted to test something completely different and
stumbled over that internal error by accident :-)
That being said, I had expected the same rules for concepts as for
constexpr functions indeed. It seemed quite natural (and would require
less RAM in my brain).
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