Re: [boost] C++11 decltype/SFINAE puzzler

Subject: Re: [boost] C++11 decltype/SFINAE puzzler
From: Doug Gregor (doug.gregor_at_[hidden])
Date: 2012-07-06 20:03:29

On Fri, Jul 6, 2012 at 1:23 PM, Eric Niebler <eric_at_[hidden]> wrote:
> On 7/6/2012 12:54 PM, Marc Glisse wrote:
>> On Fri, 6 Jul 2012, Eric Niebler wrote:
>>> The end result is that the user is presented with an error like: "no
>>> viable function A, template substitution failed." The user is given no
>>> information about which function in the chain failed to compile, or why.
>>> This is a serious usability problem!
>>
>> ... in your compiler.
>>
>>> All suggestions welcome,
>>
>> Use g++.
> <snip informative backtrace>
>
> Ah! Thanks. I'm using clang. I agree, it's a compiler QoI issue. I'll
> follow up with them.

FWIW, top-of-tree Clang produces:

t.cpp:12:3: error: no matching function for call to 'f'
  f(0);
  ^
t.cpp:8:8: note: candidate template ignored: substitution failure
      [with T = int]: no matching function for call to 'g'
  auto f(T x) -> decltype(g(x)) { return g(x); };
       ^                  ~

Which could probably still be improved, although I can't convince
myself that GCC 4.8 is doing us favors by producing the complete
SFINAE backtrace.

  - Doug