Re: [boost] [config] What Feature is this??

Subject: Re: [boost] [config] What Feature is this??
From: Peter Dimov (lists_at_[hidden])
Date: 2017-07-23 18:58:30

John Maddock wrote:
> Folks, I think I'm looking to add a new C++11 defect macro, but don't know 
> what the feature is called, nor can I see a way of detecting it with 
> clang's __has_feature function.
>
> The code I want to enable involves function overloading based on a 
> decltype return type as in:
>
> auto integrate(args...) -> decltype(expression1);
> auto integrate(args...) -> decltype(expression2);
>
> where expression1 and expression2 are two mutually exclusive options (the 
> conceptual requirements of args means that only one of these 2 will ever 
> be satisfied).
>
> This works fine in msvc-14 and later and gcc-4.8 and later, but I don't 
> see any current config macros which cover this case, nor can I figure out 
> what this trick should be called.

This is in principle just a combination of BOOST_NO_CXX11_DECLTYPE, 
BOOST_NO_CXX11_TRAILING_RESULT_TYPES and BOOST_NO_SFINAE_EXPR, although 
depending on `expression1`, BOOST_NO_CXX11_DECLTYPE_N3276 may also be 
relevant.

That's without taking into account bugs, of course.