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

Subject: Re: [boost] C++11 decltype/SFINAE puzzler
From: Nathan Ridge (zeratul976_at_[hidden])
Date: 2012-07-06 20:43:23

> From: doug.gregor_at_[hidden]
> 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.

I think that as a matter of principle, more information is better than
less. The raw error message can relatively easily be parsed by a tool 
that filters out undesired detail, but if the detail is not emitted in
the first place, it's gone.

Regards,
Nate