switch_with_template.cc

#include <iostream>

using namespace std;

template<bool Flag>
class Hello {
    public:
        void hello() const {
            if constexpr (Flag) {
                std::cout << "Wahoooo\n";
            } else {
                std::cout << "Yahoooo\n";
            }
        }
};

int main(int argc, char *argv[]) {
    if (argc > 1) {
        const auto hello = Hello<true>();
        hello.hello();
    } else {
        const auto hello = Hello<false>();
        hello.hello();
    }
    return 0;
}