Re: [Boost-users] BOOST_RESULT_OF_USE_DECLTYPE not default on C++11 compilers

Subject: Re: [Boost-users] BOOST_RESULT_OF_USE_DECLTYPE not default on C++11 compilers
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2012-01-26 10:35:54

On Wed, 25 Jan 2012, Eric Niebler wrote:

> On 1/25/2012 6:42 PM, Jeremiah Willcock wrote:
>> At least on GCC 4.6 in C++0x (C++11) mode, BOOST_RESULT_OF_USE_DECLTYPE
>> is not set by default, preventing classes such as
>> boost::transform_iterator from working on built-in lambda expressions.
>> Is there a reason that the use of decltype is not on by default for
>> compilers that support it, perhaps with a flag to force emulation mode
>> (like Boost.Move supports)?
>
> It's not the default because when we made it the default, all heck broke
> loose. Partly it was because of buggy libraries that returned a
> different type from operator() than their nested result<> template
> declared. Partly, it was due to a bug in the specification of decltype
> that was only resolved in closing minutes with the adoption of N3276[*].
> And partly it is because of continuing non-compliance of compilers that
> don't property implement N3276.

Would it be possible to use decltype to at least handle C++11 lambdas 
(which are the one case where normal result_of is broken)?  Is there a 
type trait to detect those?

-- Jeremiah Willcock