Weak pointer to this in constructor

Question

I understand it is not possible to obtain a shared_ptr by calling shared_from_this() from the constructor of a class, as the object is not yet constructed. Is it possible however to obtain a weak_ptr to the object from the constructor? Some boost forum posts discussing a "weak_from_raw()" method suggests that it may be possible.

Edit: Boost form discussing weak_from_raw http://lists.boost.org/boost-users/2010/08/61541.php

Answer 1

I think what you're referencing is this. Which seems not to have been merged to the boost release (may be wrong about that).

From the boost docs:

Frequently Asked Questions

Q. Can an object create a weak_ptr to itself in its constructor?

A. No. A weak_ptr can only be created from a shared_ptr, and at object construction time no shared_ptr to the object exists yet. Even if you could create a temporary shared_ptr to this, it would go out of scope at the end of the constructor, and all weak_ptr instances would instantly expire.

The solution is to make the constructor private, and supply a factory function that returns a shared_ptr:

class X
{
private:

    X();

public:

    static shared_ptr<X> create()
    {
        shared_ptr<X> px(new X);
        // create weak pointers from px here
        return px;
    }
};