Re: [boost] [config] Visual C++ 2013 RC support - variadic template failures

Subject: Re: [boost] [config] Visual C++ 2013 RC support - variadic template failures
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2013-09-20 12:30:18

On 20 Sep 2013 at 10:51, Beman Dawes wrote:

> I updated boost/config Visual C++ support yesterday to add Visual C++ 2013
> RC support. But Mat Berchtold reported that signals2 tests then started to
> fail. I confirmed that 2013 RC tests were failing for signals2 and several
> of its dependencies, and narrowed it down to variadic templates so reverted
> to defining BOOST_NO_CXX11_VARIADIC_TEMPLATES for 2013 RC.

I fear the cause may be the same brittle N3276 decltype VS2013 
implementation I found breaking my variadic template overloads in 
AFIO. The main problem I found is that VS2013's decltype is too quick 
to generate compile errors when fed an attempt to invoke call on a 
non-callable.

I tried working around the problem by trying to partially specialise 
a filter template type with all callable types in order to avoid 
doing a decltype on slightly incorrect input. I was successful in all 
but lambda types, because I couldn't figure out how to get VS2013 to 
select a partial specialisation for lambda types i.e. I didn't figure 
out how to replicate the trick on VS2013 of accessing the call 
operator in the unknown lambda type like you can do on GCC or clang.

I ran out of time to experiment further, so I hacked out the opposite 
filter of disabling the variadic overload for known non-variadic 
overloads and diverting everything else to the variadic overload.

I hope this is useful to anyone else facing the same problem.

Niall

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