What's the best way to run an expensive initialization?

Question

I\'ve got a singleton that is expensive to initialize:

struct X {...};

const X&
get_X()
{
    static const X x = init_X();
    return x;
}

Answer 1

If you don't mind the delay when your application starts, you could make x as a static private member of the class, like this

#include 

class X {
public:
    static X const& get_x();
private:
    static X const x;

    X()
    {
        std::cout << "X init" << std::endl;
    }
};

int main()
{
    std::cout << "Enter main" << std::endl;
    X::get_x();
    return 0;
}

X const X::x;

X const& X::get_x()
{
    return X::x;
}