Re: [boost] [result_of] now uses decltype on release branch

Subject: Re: [boost] [result_of] now uses decltype on release branch
From: Joel de Guzman (djowel_at_[hidden])
Date: 2012-09-05 12:05:17

On 9/5/12 11:12 PM, Eric Niebler wrote:
> On 9/4/2012 10:32 PM, Jeffrey Lee Hellrung, Jr. wrote:
>> In any case, I still think your use of result_of in the given example
>> was brittle and, ultimately, a misuse, whether we're speaking of the
>> TR1-based or the decltype-based result_of.
>
> Yes.
>
>> AFAIK, result_of has never had any guarantees as far as instantiating
>> it with invalid call signatures.
>
> Correct. And in C++11, std::result_of doesn't make that guarantee
> either. From Table 53 in 20.7.6.6 describing the requirements of
> std::result_of:
>
> "Fn shall be a function object type (20.8), reference to function, or
> reference to function object type. The expression
> decltype(declval<Fn>()(declval<ArgTypes>()...)) shall be well formed."
>
> Joel, I know you're annoyed by this change. But in truth, you were
> relying on an implementation detail of result_of. The list of gotchas in
> the release notes will include this case.

I am not in anyway annoyed. I am just pointing out the problems of
result_of in real code. You keep in saying "you". In fact, it's not
me. That part of the code is Tobias'; The phoenix-3 code using
result_of is Thomas', keep in mind that Phoenix-2 uses its own
result protocol.

Regards,
-- 
Joel de Guzman
http://www.boostpro.com
http://boost-spirit.com