outptr.hpp

// http://stackoverflow.com/questions/31651925/using-unique-ptr-shared-ptr-with-api-functions-returning-resources-as-out-para

template<typename P, typename T = typename P::element_type>
class outptr
{
    T* _p; P& _sp;
public:
    outptr(P& sp) throw() : _p(nullptr), _sp(sp) { }
    ~outptr() throw() { _sp.reset(_p); }
    T** operator&() throw() { return &_p; }
};

template<typename T>
inline outptr<std::shared_ptr<T>> out(std::shared_ptr<T>& p)
{
    return outptr<std::shared_ptr<T>>(p);
}

template<typename T, typename D>
inline outptr<std::unique_ptr<T, D>> out(std::unique_ptr<T, D>& p)
{
    return outptr<std::unique_ptr<T, D>>(p);
}

// template<typename P>
// inline outptr<P> out(P& p)
// {
//     return outptr<P>(p);
// }