make_unique and perfect forwarding

Question

Why is there no std::make_unique function template in the standard C++11 library? I find

std::unique_ptr p(new SomeUs         


        

Answer 1

Nice, but Stephan T. Lavavej (better known as STL) has a better solution for make_unique, which works correctly for the array version.

#include 
#include 
#include 

template 
std::unique_ptr make_unique_helper(std::false_type, Args&&... args) {
  return std::unique_ptr(new T(std::forward(args)...));
}

template 
std::unique_ptr make_unique_helper(std::true_type, Args&&... args) {
   static_assert(std::extent::value == 0,
       "make_unique() is forbidden, please use make_unique().");

   typedef typename std::remove_extent::type U;
   return std::unique_ptr(new U[sizeof...(Args)]{std::forward(args)...});
}

template 
std::unique_ptr make_unique(Args&&... args) {
   return make_unique_helper(std::is_array(), std::forward(args)...);
}

This can be seen on his Core C++ 6 video.

An updated version of STL's version of make_unique is now available as N3656. This version got adopted into draft C++14.