Code to try multiple attempts at creating a single object

call_until_not_nullptr.hpp

#include <iostream>


template <typename F, typename... Fs>
auto call_until_not_nullptr(F&& f,  Fs&&... fs) -> decltype(f()) {
    if(auto v = f()) {
        return v;
    } else {
        if constexpr(sizeof...(fs) != 0) {
            return call_until_not_nullptr(std::forward<Fs>(fs)...);
        } else {
            return nullptr;
        }
    }
}


int main(int argc, char * argv[]) {
    int a = 0;
    call_until_not_nullptr(
            [&a]() -> int* { 
            std::cout << "Returning a ptr" << std::endl;
            return &a; 
            }
            , 
            []() -> int* { 
            std::cout << "Returning nullptr" << std::endl;
            return nullptr; 
            }
            );

    std::cout << "Calls a few times" << std::endl;
    std::cout << "=================" << std::endl;
    call_until_not_nullptr(
            []() -> int* { 
            std::cout << "Returning nullptr" << std::endl;
            return nullptr; 
            }
            , 
            []() -> int* { 
            std::cout << "Returning nullptr" << std::endl;
            return nullptr; 
            }
            , 
            []() -> int* { 
            std::cout << "Returning nullptr" << std::endl;
            return nullptr; 
            }
            , 
            [&a]() -> int* { 
            std::cout << "Returning a ptr" << std::endl;
            return &a; 
            }
            );

}