[boost] shared_from_this() fails from boost.serialization load()

Subject: [boost] shared_from_this() fails from boost.serialization load()
From: Allan Johns (allan.johns_at_[hidden])
Date: 2011-02-18 01:28:21

Hi,

Consider class A, which contains an instance of class B, which in turn
contains a weak reference to its parent A instance (note: pseudocode):

class A;

class B {
    weak_ptr<A> m_parent;
}

class A {
  shared_ptr<B> m_child;
}

I have a case where I am boost-serializing class A, and its load() method
looks like so:

template<class Archive>
void A::load(Archive& ar, const unsigned int)
{
  ar & m_child;
  m_child->m_parent = shared_from_this();
}

Note that B does *not* serialize its m_parent member (this is by design).

The problem I have is that the shared_from_this() call in A::load() fails,
even though I am guaranteeing that A is serialized via a shared_ptr.
Presumably boost.serialize is not placing the default-constructed instance
of A into its containing shared_ptr<A>, before calling A::load().

My question is, is there any reason why boost.serialize couldn't deal with
this special case, which would allow me to call shared_from_this() from
load()?

I don't have a workaround for this in my code, other than to resort to a raw
ptr for B::m_parent.

ps - I suppose you could argue that since you can't do this in A's
constructor, you shouldn't be able to do it in its load() function either.
However I do have a legitimate case where I need to do this... I can
extrapolate on the whole situation if necessary, but I've left it out here
in the interests of simplicity).

Thanks boosters,
Allan