Add free std::swap() specialization function for rcp

include/rcp.h

@@ -246,6 +246,12 @@ 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>

tests.cpp

@@ -376,6 +376,9 @@ 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()