Re: [boost] [smart_ptr] Some questions

From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2008-04-10 10:59:05

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On Thursday 10 April 2008 09:57 am, Daniel Frey wrote:
> On Thu, 2008-04-10 at 09:27 -0400, Frank Mori Hess wrote:
> > Also, on further thought, I don't think enable_shared_from_this_base
> > needs to be a template class at all.
>
> If you have an easier implementation without further overhead, I'd be
> happy to see it.

This patch against trunk illustrates what I have in mind:  shared_ptr_observer 
doesn't need to be a template class.  I derived enable_shared_from_this from 
shared_ptr_observer so I could verify it still passes all the smart_ptr 
tests.

- -- 
Frank
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Index: boost/enable_shared_from_this.hpp
===================================================================
--- boost/enable_shared_from_this.hpp	(revision 44150)
+++ boost/enable_shared_from_this.hpp	(working copy)
@@ -21,7 +21,7 @@
 namespace boost
 {
 
-template<class T> class enable_shared_from_this
+template<class T> class enable_shared_from_this: public shared_ptr_observer
 {
 // dynamic cast to template type doesn't work in constructor, so we have
 // to use lazy initialization
Index: boost/shared_ptr.hpp
===================================================================
--- boost/shared_ptr.hpp	(revision 44150)
+++ boost/shared_ptr.hpp	(working copy)
@@ -52,6 +52,8 @@
 template<class T> class weak_ptr;
 template<class T> class enable_shared_from_this;
 
+class shared_ptr_observer {};
+
 namespace detail
 {
 
@@ -93,11 +95,11 @@
 
 struct ignore_enable_shared_from_this_tag {};
 
-template<class T, class Y> void sp_enable_shared_from_this( boost::shared_ptr<Y> * ptr, boost::enable_shared_from_this<T> const * pe )
+template<class T, class Y> void sp_enable_shared_from_this( boost::shared_ptr<Y> * ptr, T *pt, boost::shared_ptr_observer const *)
 {
-    if(pe != 0)
+    if(pt)
     {
-        pe->_internal_accept_owner(*ptr);
+        pt->_internal_accept_owner(*ptr);
     }
 }
 
@@ -110,7 +112,7 @@
     template<class T> sp_any_pointer( T* ) {}
 };
 
-inline void sp_enable_shared_from_this( sp_any_pointer, sp_any_pointer )
+inline void sp_enable_shared_from_this( sp_any_pointer, sp_any_pointer, sp_any_pointer )
 {
 }
 
@@ -131,6 +133,11 @@
 
 #endif // _MANAGED
 
+template<class T, class Y> void sp_enable_shared_from_this( boost::shared_ptr<Y> * ptr, T *pt)
+{
+	sp_enable_shared_from_this( ptr, pt, pt );
+}
+
 #if !defined( BOOST_NO_SFINAE ) && !defined( BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION ) && !defined( BOOST_NO_AUTO_PTR )
 
 // rvalue auto_ptr support based on a technique by Dave Abrahams

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