On Mon, Jul 6, 2009 at 11:07 AM, Frank Mori Hess<frank.hess@nist.gov> wrote:
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On Monday 06 July 2009, Zachary Turner wrote:
You shouldn't have to store 2 function pointers for every intrusive_ptr object. You should only have to store 2 function pointers per instance pointed to, and then 1 reference to some shared structure in each intrusive_ptr object. Much like shared_ptr currently does.
You'd still need a pointer in every intrusive_ptr object to point at the shared_structure, plus you'd have to do dynamic allocation of the shared object. That is never going to fly.
- From the "main reasons to use intrusive_ptr" section of its documentation:
"The memory footprint of intrusive_ptr is the same as the corresponding raw pointer;"
I'm not sure if this does what the OP wants, but the ref counting could be a policy: template <typename T> default_intrusive_ptr_refcount_policy { static void add_ref(T * t) { // by default call the global function intrusive_ptr_add_ref(t); } static void remove_ref(T * t) { // by default call the global function intrusive_ptr_remove_ref(t); } }; template intrusive_ptr<typename T, typename RefCountPolicy = default_intrusive_ptr_refcount_policy<T> > { // intrusive_ptr details... // on add ref, we call RefCountPolicy::add_ref(t) // on remove ref, we call RefCountPolicy::remove_ref(t) }; // examples: struct Foo { ... }; struct Bar { ... }; intrusive_ptr<Foo> pFoo; // usual intrusive_ptr, same as always struct BarRefCountPolicy1 { static add_ref(Bar * bar) { // add ref to bar some way }; static remove_ref(Bar * bar) { // remove ref some way } }; struct BarRefCountPolicy2 { static add_ref(Bar * bar) { // add ref to bar some *pther* way }; static remove_ref(Bar * bar) { // remove ref some *other* way } }; intrusive_ptr<Bar, BarRefCountPolicy1> pBar1; intrusive_ptr<Bar, BarRefCountPolicy2> pBar2; For better or worse... ? Tony