Enforce variadic template of certain type

Question

I would like to enforce the type of variadic template to be identical to an earlier set template type. In the below example, I\'d like T and U to be the same type.

c

Answer 1

If all parameters are required to be the same type AND the number of parameters is variable,

Variadic templates are too heavy for those requirements, just use C++11 std::initializer_list.

They just do the job if you can replace () with {} on the call.

template struct Foo {
    Foo(T val) {
        std::cout << "Called single argument ctor" << std::endl;
    }
    // Enforce all parameters to be the same type :
    Foo( std::initializer_list values ) {
        std::cout << "Called multiple argument ctor" << std::endl;
        for (T value : values)
            cout << value << endl;
    }
};

int main() {
    // Work as expected.
    Foo single(1);
    // Work as expected.
    Foo multiple{ 1, 2, 3, 4, 5 };
    // Doesn't work - as required :
    //Foo mixedtype{ 1, "a", "b", "c" };

}