a4z_blog_2017_08_18_v1, C++ (gcc)

Language: Layout:

//g++  5.4.0

#include <iostream>
#include <type_traits>

template<typename WANTED, typename...>
struct can_be_used_as : std::true_type
{};

template<typename WANTED, typename HEAD, typename... TAIL>
struct can_be_used_as<WANTED, HEAD, TAIL...>
    : std::integral_constant<bool,
                            (std::is_same<WANTED,HEAD>{} ||
                             std::is_base_of<WANTED,HEAD>{} ||
                             std::is_convertible<HEAD,WANTED>{}) &&
                            can_be_used_as<WANTED, TAIL...>{}>
{};

template<typename... strings>
std::string join_with(const std::string& what,
                      const std::string& head,
                      const strings&... tail)
{
  static_assert(can_be_used_as<std::string, strings...>{},
      "only std::string compatible arguments allowed, "
      "please convert given arguments to string");
  std::string out{head};
  auto join = [&](const auto& s){out+= what+s; };
  (void)join  ; // maybe unused, in case of join_with ("/", "a") ;
  int dummy[] = { 0, ( (void) join(tail), 0) ... };
  (void)dummy;  // for sure unused
  return out ;
}

int main ()
{
   const std::string a{"a"};
   std::cout << "JOIN " << join_with("/", a , "hurra");

// uncomment to see the error message 
   //std::cout << "JOIN " << join_with("\\", "2", 2) << std::endl;;

return 0 ;
}

Show compiler warnings [ + ] Compiler args [ + ] Show input
Compilation time: 0.43 sec, absolute running time: 0.09 sec, cpu time: 0.03 sec, memory peak: 3 Mb, absolute service time: 0,53 sec