[Bug c++/43054] New: [C++0x] ambiguous overload from identical declarations using decltype

[redi at gcc dot gnu dot org]

template<typename R> struct future { };

#ifndef NO_PROTO
template<typename Fn, typename... Args>
 auto
 async(Fn&& fn, Args&&... args)
 -> future<decltype(fn(args...))>;
#endif

template<typename Fn, typename... Args>
 auto
 async(Fn&& fn, Args&&... args)
 -> future<decltype(fn(args...))>;

int work2(int value);

void work(int value)
{
 auto handle = async(work2, value);
}

trunk gives this error:

$ g++45 -std=c++0x -c -fmessage-length=70 pr42819.min2.cc
pr42819.min2.cc: In function 'void work(int)':
pr42819.min2.cc:19:34: error: call of overloaded 'async(int (&)(int),
   int&)' is ambiguous
pr42819.min2.cc:6:2: note: candidates are: future<decltype
   (fn(async::args ...))> async(Fn&&, Args&& ...) [with Fn = int
   (&)(int), Args = {int&}, decltype (fn(async::args ...)) = int]
pr42819.min2.cc:12:2: note:                 future<decltype
   (fn(async::args ...))> async(Fn&&, Args&& ...) [with Fn = int
   (&)(int), Args = {int&}, decltype (fn(async::args ...)) = int]
pr42819.min2.cc:19:34: error: unable to deduce 'auto' from
   '<expression error>'

The declarations are identical and the error goes away if you define NO_PROTO.


-- 
           Summary: [C++0x] ambiguous overload from identical declarations
                    using decltype
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: redi at gcc dot gnu dot org
OtherBugsDependingO 42819
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43054