How can I create a C++ constructor that accepts a variable number of int's

Question

Is it possible to constrain the type of arguments in a variadic constructor?

I want to be able to express

X x1(1,3,4);
X x2(3,4,5);

// syntax error: identifier 'Args'
class X {
template<int ... Args> X(Args...)
{
}
};
// this works but allows other types than int
class Y {
template<typename ... Args> Y(Args...)
{
}
};

edit to clarify intent:

What I want to achieve is to store data passed into a constructor (constants known at compile time) into a static array.

so there are some other

template<int ...values>
struct Z
{
    static int data[sizeof...(values)];
};

template<int ... values>
int Z<values...>::data[sizeof...(values)] = {values...};

and in the constructor of X I would like to use Z like this:

class X {
    template<int ... Args> X(Args...)
    {
        Z<Args...>::data // do stuff with data
    }
};

Is that possible, our do I have to use integer_sequence?

Answer 1

You can use std::initializer_list:

#include <iostream>
#include <initializer_list>

void myFunc(std::initializer_list<int> args)
{
    for (int i: args) std::cout << i << '\n';
}
int main(){

    myFunc({2,3,2});
    // myFunc({2,"aaa",2}); error!

}

Answer 2

Since you have the following:

template<int... values>
struct Z
{
    static int data[ sizeof...( values ) ];
};

template <int... values>
int Z<values...>::data[ sizeof...( values ) ] = { values... };

You can use std::integer_sequence<> to pass in the ints to Z<>:

struct X
{
    template <int... values>
    X( std::integer_sequence<int, values...> )
    {
        for ( int i{ 0 }; i < sizeof...( values ); ++i )
            Z<values...>::data[ i ]; // do stuff with data
    }
};

You can make yourself a helper type to make it easy to call the ctor:

template <int... values>
using int_sequence = std::integer_sequence<int, values...>;

Then you can instantiate your class like so:

int main()
{
    X x( int_sequence<1, 3, 5>{} );
}