static_if

#include <iostream>
#include <type_traits>

#include <cstdlib>

template< bool condition >
void
f(char const * message = "")
{
    auto a = [&] (std::true_type) { std::cout << __PRETTY_FUNCTION__ << ' ' << message << std::endl; };
    auto b = [&] (std::false_type) { std::cout << __PRETTY_FUNCTION__ << ' ' << message << std::endl; };
    struct static_if : decltype(a), decltype(b)
    {
        using decltype(a)::operator ();
        using decltype(b)::operator ();
        static_if(decltype(a) _a, decltype(b) _b)
            : decltype(a){_a}, decltype(b){_b}
        { ; }
    };
    static_if{a, b}(std::integral_constant< bool, condition >{});
}

int
main()
{
    f< true >("Success!");
    f< false >("Failure!");
    return EXIT_SUCCESS;
}