templated_ctor.cpp

// Templated constructor in derived class.

#include <utility>

struct B {
    B();

    B(int);

    B(const B&);
    B(B&&);

    int payload[24];
};

struct D : B {
    D();

    D(double);

    D(const D&);
    D(D&&);

    template<class ...Ts>
    D(Ts&&... args)
        : B(std::forward<Ts...>(args)...) {}

    int more_payload[42];
};

void f() {
    // Calls D::D()
    D d0;

    // Calls D::D(int)
    D d1{42};

    // Calls D::D(const D&) not the templated constructor.
    D d2{d1}; 

    // Calls D::D(double)
    D d3{3.14};

    // Calls D::D<float>, not D::D(double)
    D d4{3.14f};
}