Allow get_rcp() to be called on a const reference

include/rcp.h

@@ -297,9 +297,9 @@ rcp<T> rcp_dynamic_cast(rcp<U> && other)
 
 #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

@@ -114,6 +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;
@@ -423,6 +433,7 @@ 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();