"Peter Dimov" <pdimov@mmltd.net> wrote in message news:00fc01c3f16c$e59d0220$1d00a8c0@pdimov2...
Ulrich Eckhardt wrote:
Greetings! Firstly, this is not a regression, the behaviour was present in 1.30, too. I have attached a simple program that should demonstrate the behaviour, but the core is these lines, with foo being derived from enable_shared_from_this:
// 1 std::auto_ptr<foo> g(new foo); boost::shared_ptr<foo> f(g); // 2 std::auto_ptr<foo> g(new foo); boost::shared_ptr<foo const> f(g); // 3 std::auto_ptr<foo const> g(new foo); boost::shared_ptr<foo const> f(g);
In all three cases, I'd expect to be able to call shared_from_this(). However, only the first two cases really work. I think it boils down to the function detail::sp_enable_shared_from_this() in the ctor of shared_ptr<> that takes an auto_ptr<>.
This is, well, "by design". enable_shared_from_this requires that at least one shared_ptr "owns" the plain address of the object (without any cv qualifiers.)
Why not make the _internal_weak_this member of enable_shared_from_this mutable? As I understand it, an enable_shared_from_this<X> basically undergoes two-phase construction: phase one at actual construction time, and phase two when it is put into a shared_ptr. As an extra safety measure, you could make _internal_weak_this a private member and make all shared_ptr<Y>'s friends of enable_shared_from_this (for compilers that allow template friends). Joe Gottman