How to implement make_unique function in C++11?

Question

My compiler doesn't support make_unique. How to write one?

template< class T, class... Args > unique_ptr<T> make_unique( Args&&... args );

Solution 1

Copied from make_unique and perfect forwarding (the same is given in Herb Sutter's blog)

template<typename T, typename... Args>
std::unique_ptr<T> make_unique(Args&&... args)
{
    return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
}

If you need it in VC2012, see Is there a way to write make_unique() in VS2012?

---

Nevertheless, if the solution in sasha.sochka's answer compiles with your compiler, I would go with that one. That is more elaborate and works with arrays as well.

Solution 2

Version by Stephan T. Lavavej (also known by STL) who originally proposed adding this function to C++14

#include <cstddef>
#include <memory>
#include <type_traits>
#include <utility>

namespace std {
    template<class T> struct _Unique_if {
        typedef unique_ptr<T> _Single_object;
    };

    template<class T> struct _Unique_if<T[]> {
        typedef unique_ptr<T[]> _Unknown_bound;
    };

    template<class T, size_t N> struct _Unique_if<T[N]> {
        typedef void _Known_bound;
    };

    template<class T, class... Args>
        typename _Unique_if<T>::_Single_object
        make_unique(Args&&... args) {
            return unique_ptr<T>(new T(std::forward<Args>(args)...));
        }

    template<class T>
        typename _Unique_if<T>::_Unknown_bound
        make_unique(size_t n) {
            typedef typename remove_extent<T>::type U;
            return unique_ptr<T>(new U[n]());
        }

    template<class T, class... Args>
        typename _Unique_if<T>::_Known_bound
        make_unique(Args&&...) = delete;
}

EDIT: updated code to the N3656 standard revision