Add github link in rcp.h

README.md

@@ -319,6 +319,7 @@ for (auto & l : g_listeners) l->events_received++;
 
 | | `rcp` | `std::shared_ptr` |
 |---|---|---|
+| Pointer size | One pointer | Two pointers (object + control block) |
 | Reference count location | Inside the object | Separate control block (extra allocation) |
 | Class requirement | `rcp_managed_root` / `rcp_managed` macro | None (any type) |
 | Weak pointers | No | Yes (`std::weak_ptr`) |
@@ -326,7 +327,14 @@ for (auto & l : g_listeners) l->events_received++;
 | Pointer to `this` | implicit conversion from `this` or explicit `get_rcp()` | `std::enable_shared_from_this` |
 | Checked downcast | `rcp_dynamic_cast` | `std::dynamic_pointer_cast` |
 
-The intrusive design means each managed object requires only one heap
+Because `rcp` stores only a single raw pointer, `sizeof(rcp<T>)` equals
+`sizeof(T *)` — typically 8 bytes on a 64-bit platform.
+`std::shared_ptr` stores both a pointer to the object and a pointer to the
+control block, so `sizeof(std::shared_ptr<T>)` is typically 16 bytes.
+This makes `rcp` more efficient to pass by value, copy, and store in
+containers.
+
+The intrusive design also means each managed object requires only one heap
 allocation instead of two which can improve performance for many applications.
 The trade-off is that the class must be written with `rcp` in mind.
 

include/rcp.h

@@ -28,6 +28,9 @@
 
 /**
  * Reference-counting pointer.
+ *
+ * See https://github.com/holtrop/rcp for documentation, issues, and pull
+ * requests.
  */
 template <typename T>
 class rcp
@@ -81,7 +84,7 @@ public:
 
     rcp & operator=(rcp && other) noexcept
     {
-        if (ptr != other.ptr)
+        if (this != &other)
         {
             if (ptr)
             {
@@ -113,12 +116,17 @@ public:
     }
 
     template <typename U>
-    rcp(rcp<U> && other) : ptr(static_cast<T *>(other.ptr))
+    rcp(rcp<U> && other) noexcept : ptr(static_cast<T *>(other.ptr))
     {
         static_assert(std::is_base_of<T, U>::value, "rcp: implicit cast must be an upcast");
         other.ptr = nullptr;
     }
 
+    int use_count() const
+    {
+        return ptr ? ptr->rcp_count() : 0;
+    }
+
     void swap(rcp & other) noexcept
     {
         T * tmp = ptr;
@@ -167,6 +175,38 @@ public:
         return static_cast<const void *>(ptr) != static_cast<const void *>(other.ptr);
     }
 
+    template <typename U>
+    bool operator<(const rcp<U> & other) const
+    {
+        return std::less<const void *>()(
+            static_cast<const void *>(ptr),
+            static_cast<const void *>(other.ptr));
+    }
+
+    template <typename U>
+    bool operator<=(const rcp<U> & other) const
+    {
+        return !std::less<const void *>()(
+            static_cast<const void *>(other.ptr),
+            static_cast<const void *>(ptr));
+    }
+
+    template <typename U>
+    bool operator>(const rcp<U> & other) const
+    {
+        return std::less<const void *>()(
+            static_cast<const void *>(other.ptr),
+            static_cast<const void *>(ptr));
+    }
+
+    template <typename U>
+    bool operator>=(const rcp<U> & other) const
+    {
+        return !std::less<const void *>()(
+            static_cast<const void *>(ptr),
+            static_cast<const void *>(other.ptr));
+    }
+
     bool operator==(std::nullptr_t) const
     {
         return ptr == nullptr;
@@ -187,6 +227,18 @@ public:
     friend rcp<V> rcp_dynamic_cast(rcp<W> && other);
 };
 
+template <typename T>
+bool operator==(std::nullptr_t, const rcp<T> & p)
+{
+    return p == nullptr;
+}
+
+template <typename T>
+bool operator!=(std::nullptr_t, const rcp<T> & p)
+{
+    return p != nullptr;
+}
+
 namespace std
 {
     template <typename T>
@@ -197,6 +249,12 @@ namespace std
             return hash<const void *>()(static_cast<const void *>(p.get_raw()));
         }
     };
+
+    template <typename T>
+    void swap(rcp<T> & a, rcp<T> & b) noexcept
+    {
+        a.swap(b);
+    }
 }
 
 template <typename T, typename U>
@@ -220,27 +278,31 @@ rcp<T> rcp_dynamic_cast(rcp<U> && other)
 }
 
 #define rcp_managed_root(classname) \
-    public: \
+    private: \
+        mutable std::atomic<int> rcp_ref_count{0}; \
         void rcp_inc() const \
         { \
-            ref_count.fetch_add(1, std::memory_order_relaxed); \
+            rcp_ref_count.fetch_add(1, std::memory_order_relaxed); \
         } \
         void rcp_dec() const \
         { \
-            if (ref_count.fetch_sub(1, std::memory_order_acq_rel) == 1) \
+            if (rcp_ref_count.fetch_sub(1, std::memory_order_acq_rel) == 1) \
             { \
                 delete this; \
             } \
         } \
-    private: \
-        mutable std::atomic<int> ref_count{0}; \
+        int rcp_count() const \
+        { \
+            return rcp_ref_count.load(std::memory_order_relaxed); \
+        } \
+        template <typename RCP_T_> friend class rcp; \
     rcp_managed(classname)
 
 #define rcp_managed(classname) \
     public: \
-        rcp<classname> get_rcp() \
+        rcp<classname> get_rcp() const \
         { \
-            return rcp<classname>(this); \
+            return rcp<classname>(const_cast<classname *>(this)); \
         } \
         template <typename... Args> \
         static rcp<classname> create(Args&&... args) \

tests.cpp

@@ -1,5 +1,6 @@
 #include <rcp.h>
 #include <cassert>
+#include <map>
 #include <unordered_map>
 #include <vector>
 
@@ -83,6 +84,8 @@ void test_booleans()
     rcp<MyDerived> myderived;
     assert(!myderived);
     assert(myderived == nullptr);
+    assert(nullptr != mybase);
+    assert(nullptr == myderived);
 }
 
 void test_create()
@@ -111,6 +114,16 @@ struct Receiver
     }
 };
 
+void test_get_rcp_const()
+{
+    auto a = MyObj::create();
+    const MyObj & ref = *a;
+    rcp<MyObj> b = ref.get_rcp();
+    assert(b);
+    assert(b->v == 42);
+    assert(b.use_count() == 2);
+}
+
 void test_multi_construct_from_raw_pointers()
 {
     Receiver r;
@@ -151,10 +164,28 @@ void test_listener_self_registration()
 
 void test_copy_assignment_decrements_previous_reference()
 {
-    MyB myb = MyB::create(12, 13);
-    MyB myb2 = MyB::create(14, 15);
-    myb = myb2;
-    assert(myb->x == 14);
+    int constructed_before = mybase_construct;
+    int destructed_before = mybase_destruct;
+    {
+        MyB myb = MyB::create(12, 13);
+        MyB myb2 = MyB::create(14, 15);
+        myb = myb2;
+        assert(myb->x == 14);
+        assert(mybase_destruct == destructed_before + 1);
+    }
+    assert(mybase_construct == constructed_before + 2);
+    assert(mybase_destruct == destructed_before + 2);
+}
+
+void test_self_assignment()
+{
+    int destructed_before = mybase_destruct;
+    MyB a = MyB::create(1, 2);
+    a = a;
+    assert(a);
+    assert(a->x == 1);
+    assert(a.use_count() == 1);
+    assert(mybase_destruct == destructed_before);
 }
 
 void test_move_constructor()
@@ -190,6 +221,18 @@ void test_move_assignment()
     assert(mybase_destruct == destructed_before + 1);
 }
 
+void test_move_assignment_same_object()
+{
+    MyB a = MyB::create(1, 2);
+    MyB b = a;
+    assert(a.use_count() == 2);
+    b = std::move(a);
+    assert(!a);
+    assert(b);
+    assert(b->x == 1);
+    assert(b.use_count() == 1);
+}
+
 void test_move_assignment_releases_existing()
 {
     int constructed_before = mybase_construct;
@@ -314,6 +357,39 @@ protected:
     ~Counter() { external_destruct++; }
 };
 
+void test_ordering()
+{
+    MyB a = MyB::create(1, 2);
+    MyB b = MyB::create(3, 4);
+    MyB a2 = a;
+    assert(!(a < a2));
+    assert(a <= a2);
+    assert(!(a > a2));
+    assert(a >= a2);
+    assert((a < b) != (b < a));
+    assert((a < b) == (b > a));
+    assert((a <= b) == (b >= a));
+    std::map<MyB, int> m;
+    m[a] = 1;
+    m[b] = 2;
+    assert(m[a2] == 1);
+    assert(m[b] == 2);
+}
+
+void test_use_count()
+{
+    MyB a = MyB::create(1, 2);
+    assert(a.use_count() == 1);
+    {
+        MyB b = a;
+        assert(a.use_count() == 2);
+        assert(b.use_count() == 2);
+    }
+    assert(a.use_count() == 1);
+    MyB empty;
+    assert(empty.use_count() == 0);
+}
+
 void test_swap()
 {
     MyB a = MyB::create(1, 2);
@@ -321,6 +397,9 @@ void test_swap()
     a.swap(b);
     assert(a->x == 3);
     assert(b->x == 1);
+    std::swap(a, b);
+    assert(a->x == 1);
+    assert(b->x == 3);
 }
 
 void test_hash()
@@ -334,6 +413,27 @@ void test_hash()
     assert(map.find(c) == map.end());
 }
 
+template <typename T>
+struct Box
+{
+    rcp_managed_root(Box);
+protected:
+    Box(T v) : v(v) {}
+public:
+    T v;
+};
+
+void test_class_template()
+{
+    auto a = Box<int>::create(42);
+    auto b = Box<int>::create(99);
+    assert(a->v == 42);
+    assert(b->v == 99);
+    auto c = a;
+    assert(c->v == 42);
+    assert(c.use_count() == 2);
+}
+
 void test_external_class()
 {
     int before = external_destruct;
@@ -354,13 +454,16 @@ int main(int argc, char * argv[])
     test_dereference();
     test_booleans();
     test_create();
+    test_get_rcp_const();
     test_multi_construct_from_raw_pointers();
     test_listener_self_registration();
     test_copy_assignment_decrements_previous_reference();
+    test_self_assignment();
     test_cross_type_comparison();
     test_reset();
     test_move_constructor();
     test_move_assignment();
+    test_move_assignment_same_object();
     test_move_assignment_releases_existing();
     test_upcast();
     test_move_upcast();
@@ -368,8 +471,11 @@ int main(int argc, char * argv[])
     test_dynamic_cast_failure();
     test_dynamic_cast_move_success();
     test_dynamic_cast_move_failure();
+    test_ordering();
+    test_use_count();
     test_swap();
     test_hash();
+    test_class_template();
     test_external_class();
     return 0;
 }