How do I call ::std::make_shared on a class with only protected or private constructors?

Question

I have this code that doesn\'t work, but I think the intent is clear:

testmakeshared.cpp

#include 

class A {
 public:
   stat         


        

Answer 1

Ideally, I think the perfect solution would require additions to the C++ standard. Andrew Schepler proposes the following:

(Go here for the whole thread)

we can borrow an idea from boost::iterator_core_access. I propose a new class std::shared_ptr_access with no public or protected members, and to specify that for std::make_shared(args...) and std::alloc_shared(a, args...), the expressions ::new(pv) T(forward(args)...) and ptr->~T() must be well-formed in the context of std::shared_ptr_access.

An implementation of std::shared_ptr_access might look like:

namespace std {
    class shared_ptr_access
    {
        template 
        static _T* __construct(void* __pv, _Args&& ... __args)
        { return ::new(__pv) _T(forward<_Args>(__args)...); }

        template 
        static void __destroy(_T* __ptr) { __ptr->~_T(); }

        template 
        friend class __shared_ptr_storage;
    };
}

Usage

If/when the above is added to the standard, we would simply do:

class A {
public:
   static std::shared_ptr create() {
      return std::make_shared();
   }

 protected:
   friend class std::shared_ptr_access;
   A() {}
   A(const A &) = delete;
   const A &operator =(const A &) = delete;
};

If this also sounds like an important addition to the standard to you, feel free to add your 2 cents to the linked isocpp Google Group.