Modified weak_ptr to reflect list comments.

[SVN r12793]

include/boost/detail/shared_count.hpp

@@ -31,19 +31,19 @@
 namespace boost
 {
 
-namespace detail
+class use_count_is_zero: public std::exception
-{
-
-class bad_weak_to_shared_cast: public std::exception
 {
 public:
 
     virtual char const * what() const throw()
     {
-        return "bad_weak_to_shared_cast";
+        return "use_count_is_zero";
     }
 };
 
+namespace detail
+{
+
 class counted_base
 {
 public:
@@ -75,7 +75,7 @@ public:
     void add_ref()
     {
         lightweight_mutex::scoped_lock lock(mtx_);
-        if(use_count_ == 0) throw bad_weak_to_shared_cast();
+        if(use_count_ == 0) throw use_count_is_zero();
         ++use_count_;
         ++weak_count_;
     }

include/boost/weak_ptr.hpp

@@ -30,7 +30,6 @@ private:
 
     // Borland 5.5.1 specific workarounds
     typedef weak_ptr<T> this_type;
-    typedef shared_ptr<T> shared_type;
 
 public:
 
@@ -96,53 +95,16 @@ public:
         this_type().swap(*this);
     }
 
-    shared_type get() const // never throws
+    T * get() const // never throws; unsafe in multithreaded programs!
     {
-        // optimization: avoid throw overhead
+        return use_count() == 0? 0: px;
-        if(use_count() == 0)
-        {
-            return shared_type();
-        }
-
-        try
-        {
-            return shared_type(*this);
-        }
-        catch(boost::detail::bad_weak_to_shared_cast const &)
-        {
-            return shared_type();
-        }
     }
 
-    // operator* has been removed; it's unsafe.
-
-    // operator-> retained for convenience, since it's safe
-    // in its current form.
-
-    shared_type operator-> () const // may throw
-    {
-        return shared_type(*this);
-    }
-    
     long use_count() const // never throws
     {
         return pn.use_count();
     }
 
-    // implicit conversion to "bool"
-
-    typedef long (this_type::*bool_type)() const;
-
-    operator bool_type() const // never throws
-    {
-        return px == 0 || use_count() == 0? 0: &this_type::use_count;
-    }
-
-    bool operator! () const // never throws
-    {
-        return px == 0 || use_count() == 0;
-    }
-
     void swap(this_type & other) // never throws
     {
         std::swap(px, other.px);
@@ -202,6 +164,24 @@ template<class T> void swap(weak_ptr<T> & a, weak_ptr<T> & b)
     a.swap(b);
 }
 
+template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r) // never throws
+{
+    // optimization: avoid throw overhead
+    if(r.use_count() == 0)
+    {
+        return shared_ptr<T>();
+    }
+
+    try
+    {
+        return shared_ptr<T>(r);
+    }
+    catch(use_count_is_zero const &)
+    {
+        return shared_ptr<T>();
+    }
+}
+
 template<class T, class U> weak_ptr<T> shared_static_cast(weak_ptr<U> const & r)
 {
     return weak_ptr<T>(r, detail::static_cast_tag());

shared_ptr_test.cpp

@@ -104,7 +104,8 @@ template<class T> void test_is_X(boost::shared_ptr<T> const & p)
 
 template<class T> void test_is_X(boost::weak_ptr<T> const & p)
 {
-    BOOST_TEST(p->id() == 1);
+    BOOST_TEST(p.get() != 0);
+    BOOST_TEST(p.get()->id() == 1);
 }
 
 template<class T> void test_is_Y(boost::shared_ptr<T> const & p)
@@ -115,7 +116,8 @@ template<class T> void test_is_Y(boost::shared_ptr<T> const & p)
 
 template<class T> void test_is_Y(boost::weak_ptr<T> const & p)
 {
-    BOOST_TEST(p->id() == 2);
+    BOOST_TEST(p.get() != 0);
+    BOOST_TEST(p.get()->id() == 2);
 }
 
 template<class T> void test_eq(T const & a, T const & b)
@@ -152,24 +154,12 @@ template<class T> void test_is_zero(boost::shared_ptr<T> const & p)
     BOOST_TEST(p.get() == 0);
 }
 
-template<class T> void test_is_zero(boost::weak_ptr<T> const & p)
-{
-    BOOST_TEST(!p);
-    test_is_zero(p.get());
-}
-
 template<class T> void test_is_nonzero(boost::shared_ptr<T> const & p)
 {
     BOOST_TEST(p);
     BOOST_TEST(p.get() != 0);
 }
 
-template<class T> void test_is_nonzero(boost::weak_ptr<T> const & p)
-{
-    BOOST_TEST(p);
-    test_is_nonzero(p.get());
-}
-
 int test_main(int, char * [])
 {
     using namespace boost;
@@ -228,35 +218,66 @@ int test_main(int, char * [])
         weak_ptr<X> wp1;
 
         BOOST_TEST(wp1.use_count() == 0);
-        test_is_zero(wp1);
+        BOOST_TEST(wp1.get() == 0);
+
+        try
+        {
+            shared_ptr<X> sp1(wp1);
+            BOOST_ERROR("shared_ptr<X> sp1(wp1) failed to throw");
+        }
+        catch(boost::use_count_is_zero const &)
+        {
+        }
+
+        test_is_zero(boost::make_shared(wp1));
 
         weak_ptr<X> wp2 = shared_static_cast<X>(p5);
 
         BOOST_TEST(wp2.use_count() == 1);
-        test_is_nonzero(wp2);
+        BOOST_TEST(wp2.get() != 0);
         test_is_Y(wp2);
         test_ne(wp1, wp2);
 
+        // Scoped to not affect the subsequent use_count() tests.
+        {
+            shared_ptr<X> sp2(wp2);
+            test_is_nonzero(boost::make_shared(wp2));
+        }
+
         weak_ptr<Y> wp3 = shared_dynamic_cast<Y>(wp2);
 
         BOOST_TEST(wp3.use_count() == 1);
-        test_is_nonzero(wp3);
+        BOOST_TEST(wp3.get() != 0);
         test_eq2(wp2, wp3);
 
         weak_ptr<X> wp4(wp3);
 
-        test_is_nonzero(wp4);
+        BOOST_TEST(wp4.use_count() == 1);
+        BOOST_TEST(wp4.get() != 0);
         test_eq(wp2, wp4);
 
         wp1 = p2;
-        test_is_zero(wp1);
+        BOOST_TEST(wp1.get() == 0);
+
+        // Note the following test. Construction succeeds,
+        // but make_shared() returns a null shared_ptr with
+        // use_count() == 2. 
+
+        shared_ptr<X> sp1(wp1);
+        test_is_zero(boost::make_shared(wp1));
+
+        BOOST_TEST(p2.use_count() == 2);
+        BOOST_TEST(sp1.use_count() == 2);
+        BOOST_TEST(wp1.use_count() == 2);
+
+        //
 
         wp1 = p4;
         wp1 = wp3;
         wp1 = wp2;
 
         BOOST_TEST(wp1.use_count() == 1);
-        test_is_nonzero(wp1);
+        BOOST_TEST(wp1.get() != 0);
         test_eq(wp1, wp2);
 
         weak_ptr<X> wp5;
@@ -265,16 +286,15 @@ int test_main(int, char * [])
         bool b2 = wp5 < wp1;
 
         p5.reset();
-        test_is_zero(wp5);
 
         BOOST_TEST(wp1.use_count() == 0);
-        test_is_zero(wp1);
+        BOOST_TEST(wp1.get() == 0);
 
         BOOST_TEST(wp2.use_count() == 0);
-        test_is_zero(wp2);
+        BOOST_TEST(wp2.get() == 0);
 
         BOOST_TEST(wp3.use_count() == 0);
-        test_is_zero(wp3);
+        BOOST_TEST(wp3.get() == 0);
 
         // Test operator< stability for std::set< weak_ptr<> >
         // Thanks to Joe Gottman for pointing this out