Re: [boost] [result_of] fails with clan (C++11)

Subject: Re: [boost] [result_of] fails with clan (C++11)
From: Eric Niebler (eric_at_[hidden])
Date: 2012-11-28 13:44:24

On 11/28/2012 6:14 AM, Mathias Gaunard wrote:
> On 28/11/12 08:42, Oliver Kowalke wrote:
>>>> Hello,
>>>> clang (c++11 support) fails on code like:
>>>>
>>>> BOOST_STATIC_ASSERT((
>>>>              is_same< void, typename result_of< Fn() >::type
>>>> >::value));
>>>>
>>>> with error:
>>>>
>>>>   no type named 'type' in 'boost::result_of<void (&())(X &)>'
>>>>              is_same< void, typename result_of< Fn() >::type
>>>> >::value));
>>>>                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~**~~
>>>>
>>>
>>> Does Fn == void (&)(X&) or void (X&) ? I.e., is it a unary function
>>> type?
>>
>> it's called inside a templated function:
>> template< typename Fn >
>> void g(BOOST_RV_RV( Fn) fn){
>> BOOST_STATIC_ASSERT(...)
>> ....}
> 
> remove the reference from Fn (at least in C++11).
> I don't know what the actual type of Fn is in C++03.

Did my previous answer not fully address this issue? The function type
void(&)(X&) cannot be called with 0 arguments, so a decltype-based
result_of will have the behavior your observe. The old TR1-style
result_of will give you void. At present, decltype-based result_of is
only enabled for very recent clang builds. This explains the difference.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com