Can someone please explain why this code:
struct Foo : boost::enable_shared_from_this<Foo> {}; Foo* p_foo = new Foo; boost::shared_ptr<Foo> ptr_foo(p_foo->shared_from_this());
is throwing?
At the time you call shared_from_this, no shared_ptr has been created to hold p_foo. The weak_ptr assumes the memory has been deallocated, since
Hi Dominique, Dominique Devienne wrote: there are no shared_ptrs pointing to it. Inheriting from enable_shared_from_this is a guarantee that you will store the pointer in a shared_ptr -- it's a precondition of calling shared_from_this. Since Foo embeds a weak_ptr, why can't it new the pi_ on the spot?
(I'm using Boost 1.44).
Hmm, it might be interesting to have shared_from_this create a shared_ptr if none exists, but I don't know what that might complicate -- perhaps it would cause issues at destruction?
PS: On a related note, why doesn't boost::shared_ptr<Foo>(p_foo) (where p_foo is a raw Foo*) implicitly apply the aliasing Ctor, to share the same px, to avoid the classic bug of having several different pn on the same px, since p_foo derives from enable_shared_from_this()? Initially i thought that's what sp_enable_shared_from_this() and pe->_internal_accept_owner() were meant to do, but obviously that's not the case.
I suspect something like this could be made to work if the previous also worked -- but the class is documented to *not* allow the previous to work. I'd have to think about why (or maybe Peter will enlighten us). HTH, Nate