http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50157
Bug #: 50157
Summary: [C++0x] Non-silent SFINAE in new expression with
explicit conversion
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: daniel.krueg...@googlemail.com
CC: ja...@redhat.com
Build: 4.7.0 20110813 (experimental)
gcc 4.7.0 20110813 (experimental) in C++0x mode rejects the following code:
---
template<class T>
T val();
template<class T, class Arg, class =
decltype(::new T(val<Arg>()))
>
auto test(int) -> char;
template<class, class>
auto test(...) -> char (&)[2];
struct P {
explicit operator bool(); // (#13)
};
typedef decltype(test<bool, P>(0)) type; // OK
typedef decltype(test<float, P>(0)) type2; // Error (#17)
---
"17|error: invalid user-defined conversion from 'P' to 'float' [-fpermissive]|
13|note: candidate is: P::operator bool() <near match>|
13|note: return type 'bool' of explicit conversion function cannot be
converted to 'float' with a qualification conversion|
17|error: invalid user-defined conversion from 'P' to 'float' [-fpermissive]|
13|note: candidate is: P::operator bool() <near match>|
13|note: return type 'bool' of explicit conversion function cannot be
converted to 'float' with a qualification conversion|
||=== Build finished: 6 errors, 0 warnings ===|"
It is correct, that the P->float conversion would be ill-formed, but this needs
to be handled silently and the program should be accepted. The compiler seems
to have a special problem here with the combination of an explicit conversion
function in P and the otherwise feasible bool->float conversion in implicit
contexts.
