Microsoft compiler (Visual Studio 2017 15.2) rejects the following code:
#include <type_traits>
struct B
{
template<int n, std::enable_if_t<n == 0, int> = 0>
void f() { }
};
struct D : B
{
using B::f;
template<int n, std::enable_if_t<n == 1, int> = 0>
void f() { }
};
int main()
{
D d;
d.f<0>();
d.f<1>();
}
The error is:
error C2672: 'D::f': no matching overloaded function found
error C2783: 'void D::f(void)': could not deduce template argument for '__formal'
note: see declaration of 'D::f'
Clang also rejects it:
error: no matching member function for call to 'f'
d.f<0>();
~~^~~~
note: candidate template ignored: disabled by 'enable_if' [with n = 0]
using enable_if_t = typename enable_if<_Cond, _Tp>::type;
GCC perfectly accepts it. Which compiler is right?
Addition:
With SFINAE in the form
template<int n, typename = std::enable_if_t<n == 0>>
...
template<int n, typename = std::enable_if_t<n == 1>>
GCC also produces an error:
error: no matching function for call to ‘D::f<0>()’
d.f<0>();
^
note: candidate: template<int n, class> void D::f()
void f()
^
note: template argument deduction/substitution failed:
Turning cppleaner's comment into an answer:
From namespace.udecl#15.sentence-1:
Unfortunately, template parameter doesn't count and both
f
has empty parameter-type-list, are not const and no ref-qualifier.Derived::f
so hidesBase::f
.gcc is wrong to accept that code.
So the way to fix it is by default argument (returned type doesn't count either):