https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87452
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |rejects-valid
Status|UNCONFIRMED |NEW
Last reconfirmed| |2018-09-27
Ever confirmed|0 |1
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:
extern "C" int puts(const char*);
struct vector { };
namespace N {
/**
* Write range of random access iterators to output stream.
*/
void
operator+(const vector&)
{
puts("pass");
}
template<typename T>
auto
f(const T& t)
-> decltype(operator+(t)) // OK
{
return (+t);
}
template<typename T>
auto
g(const T& t)
-> decltype(+t) // fails to find operator defined in N::
{
return (+t);
}
} // namespace N
int main()
{
vector vec;
N::f(vec);
N::g(vec);
}
87452.cc: In function 'int main()':
87452.cc:38:11: error: no matching function for call to 'g(vector&)'
38 | N::g(vec);
| ^
87452.cc:26:1: note: candidate: 'template<class T> decltype (+ t) N::g(const
T&)'
26 | g(const T& t)
| ^
87452.cc:26:1: note: template argument deduction/substitution failed:
87452.cc: In substitution of 'template<class T> decltype (+ t) N::g(const T&)
[with T = vector]':
87452.cc:38:11: required from here
87452.cc:27:13: error: no match for 'operator+' (operand type is 'const
vector')
27 | -> decltype(+t) // fails to find operator defined in N::
| ^~
As the call to N::f(t) shows, the decltype in the trailing-return-type works OK
if using function call syntax (to call either a named function or the
operator-function-id). It only fails to find the overloaded operator in the
enclosing namespace for operator syntax, i.e. decltype(+t).
