[class.inhctor.init]
Change:
Inheriting a constructor no longer injects a constructor into the derived class.
Rationale:
Better interaction with other language features.
Effect on original feature:
Valid C++ 2014 code that uses inheriting constructors may not be valid
or may have different semantics. A using-declaration
that names a constructor now makes the corresponding base class constructors
visible to initializations of the derived class
rather than declaring additional derived class constructors.
struct A {
template<typename T> A(T, typename T::type = 0);
A(int);
};
struct B : A {
using A::A;
B(int);
};
B b(42L); // now calls B(int), used to call B<long>(long),
// which called A(int) due to substitution failure
// in A<long>(long).