Using shared_from_this() in constructor

[kpedersen]

Hi all,

As you know it is not possible to use the std::enable_shared_from_this<T> and shared_from_this() pair from the constructor of an object since a shared_pointer<T> containing the class is not yet in existance. However, I really would like this functionality. I have attempted my own system and it seems to be working OK.

#ifndef KP_MEMORY_H
#define KP_MEMORY_H

#include <memory>

namespace kp
{

template <class T>
void construct_deleter(T *t)
{
  t->~T();
  free(t);
}

template <class T, typename... Params>
std::shared_ptr<T> make_shared(Params&&... args)
{
  std::shared_ptr<T> rtn;
  T *t = (T *)calloc(1, sizeof(T));
  rtn.reset(t, construct_deleter<T>);
  t->_construct_pself = &rtn;
  t = new(t) T(std::forward<Params>(args)...);
  t->_construct_pself = NULL;
  t->_construct_self = rtn;

  return rtn;
}

template <class T>
class enable_shared_from_this
{
public:
  std::shared_ptr<T> *_construct_pself;
  std::weak_ptr<T> _construct_self;

  std::shared_ptr<T> shared_from_this()
  {
    if(_construct_pself)
    {
      return *_construct_pself;
    }
    else
    {
      return _construct_self.lock();
    }
  }
};

}

#endif

Can anyone spot any flaws in this logic?

As it stands I can use it as so:

std::shared_ptr<Employee> emp = kp::make_shared<Employee>("Karsten", 30);

and in the Employee constructor:

Employee::Employee(std::string name, int age)
{
  Dept::addEmployee(shared_from_this());
}

Before I commit this to a relatively large codebase, I would really appreciate some ideas or feedback from you guys.

Thanks!