operator -> is recursive. It is applied until the initial ptr type is retrieved. operator* is not. But as I think you can try to introduce the casting operator to the contained type: template<class T> struct LockingProxy { //ctors (might be with params) that lock //dtor that unlocks //T* operator-> //T& operator* operator T&()const; private: T t; }; I assume you have following type: shared_ptr< LockingProxy<T> > ptr(new LockingProxy(params for T's ctor)); Now you could at least call it: (static_cast(*ptr)).member_of_T; Or if you need to pass the T& to some other function without casts: void do_smth(T const& t); do_smth(*ptr); You can also provide a function which makes this for you: template<class T> T& get_inst(LockingProxy<T> const& r) { return *r; } do_smth(get_inst(*ptr)); Hope that helps, Best Regards, Ovanes -----Original Message----- From: Allison Floyd [mailto:allison.floyd@gmail.com] Sent: Thursday, January 25, 2007 6:44 PM To: boost-users@lists.boost.org Subject: [Boost-users] boost::mem_fn with Alexandrescu LockingProxy Hello, the list. After some digging through the bind and mem_fn documentation, I have been unable to figure out whether I'm attempting to do something impossible or not. I've created a thread-safe variant of shared_ptr that uses Alexandrescu's LockingProxy to ensure that access to the contained object through operator-> correctly locks and unlocks the pointee object. In all respects save one, this "shared_locking_ptr" is syntactically equivalent to boost::shared_ptr. The one thing it cannot do is dereference the pointer via operator* (I can't figure out how to return something from operator* that remains in scope (and thus locked) long enough for the operation to complete). All well and good so far. Where I'm trying to use this beast is in boost::signals via bind (and therefore mem_fn). I'd like to connect a member function of an object to the signal through my shared_locking_ptr, so that when the signal fires it automatically locks the object, invokes the member function, and then unlocks. Shared pointers to objects are valid arguments to mem_fn; my shared_locking_ptr isn't, alas, apparently because it requires the operator* mentioned above. So: 1) Has anybody else attempted to extend shared_ptr for Alexandrescu's policy-based storage types, specifically the LockingProxy, and figured out how to overload operator* in a meaningful way? or 2) Is there some way to wheedle signals, bind, and/or mem_fn so that they only access the slot through operator->, and don't try to dereference it? If this is more properly a boost developer's list question, let me know and I'll take it there. Thanks! -- Allison Floyd _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Allison Floyd wrote:

Hello, the list.

After some digging through the bind and mem_fn documentation, I have been unable to figure out whether I'm attempting to do something impossible or not. I've created a thread-safe variant of shared_ptr that uses Alexandrescu's LockingProxy to ensure that access to the contained object through operator-> correctly locks and unlocks the pointee object. In all respects save one, this "shared_locking_ptr" is syntactically equivalent to boost::shared_ptr. The one thing it cannot do is dereference the pointer via operator* (I can't figure out how to return something from operator* that remains in scope (and thus locked) long enough for the operation to complete). All well and good so far.

Where I'm trying to use this beast is in boost::signals via bind (and therefore mem_fn). I'd like to connect a member function of an object to the signal through my shared_locking_ptr, so that when the signal fires it automatically locks the object, invokes the member function, and then unlocks. Shared pointers to objects are valid arguments to mem_fn; my shared_locking_ptr isn't, alas, apparently because it requires the operator* mentioned above.

mem_fn uses get_pointer(sp) to obtain a "raw pointer" which is then used as a first argument to operator->*. If you return a locking proxy from your get_pointer overload and implement operator->* for your locking proxy, it should work as you want.