more comments on new weak_ptr

From: Darin Adler (darin_at_[hidden])
Date: 2002-02-12 13:10:19

I think that it's strange that constructing a shared_ptr from a weak_ptr
that's 0 throws the boost::detail::bad_weak_to_shared_cast exception, but
using the get() operation on weak_ptr results in a shared_ptr that's 0.

I think the 0 behavior is better than the exception behavior. We can make
the bad_weak_to_shared_cast exception be an implementation detail never
exposed in the interface.

    -- Darin