http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47513
Summary: [C++0x] [SFINAE] compiler rejects valid code
Product: gcc
Version: 4.5.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: s.gesem...@gmail.com
I believe the following code should compile using the option -std=c++0x:
struct use_copy_ctor {};
struct prefer_clone_func : use_copy_ctor {};
template<class T>
auto clone(T const* ptr, prefer_clone_func)
-> decltype(ptr->clone())
{ return ptr->clone(); }
template<class T>
auto clone(T const* ptr, use_copy_ctor)
-> decltype(new T(*ptr))
{ return new T(*ptr); }
struct abc {
virtual ~abc() {}
virtual abc* clone() const =0;
};
struct derived : abc
{
derived* clone() const { return new derived(*this); }
};
int main()
{
derived d;
abc* p = &d;
abc* q = clone(p,prefer_clone_func());
delete q;
}
As far as I can tell SFINAE applies during template argument deduction where
abc is substituted for T in decltype(new T(*ptr)). GCC complains about abc
being abstract -- which it is, of course -- but it should instead simply ignore
the second function template.
Related note: Assuming std::is_constructible is implemented in terms of
decltype, this would explain why std::is_constructible doesn't work either on
abstract class types.
