Fix initial implementation and add first test

include/rcp.h

@@ -33,12 +33,9 @@ class rcp
 private:
     T * ptr = nullptr;
 
-    explicit rcp(T * p) : ptr(p)
+    void init_ptr(T * p)
     {
-        if (p)
-        {
-            ptr->rcp_inc();
-        }
+        ptr = p;
     }
 
     friend T;
@@ -54,6 +51,16 @@ public:
         }
     }
 
+    rcp<T> & operator=(const rcp & other)
+    {
+        ptr = other.ptr;
+        if (ptr)
+        {
+            ptr->rcp_inc();
+        }
+        return *this;
+    }
+
     ~rcp()
     {
         if (ptr)
@@ -93,12 +100,12 @@ class root
 private:
     mutable std::atomic<int> ref_count{0};
 
-    rcp<root> root_rcp;
+    mutable rcp<root> root_rcp;
 
 protected:
     root()
     {
-        root_rcp = rcp<root>(this);
+        root_rcp.init_ptr(this);
     }
 
     virtual ~root() = default;
@@ -111,8 +118,9 @@ public:
 
     void rcp_dec() const
     {
-        if (ref_count.fetch_sub(1, std::memory_order_acq_rel) == 0)
+        if (ref_count.fetch_sub(1, std::memory_order_acq_rel) == 1)
         {
+            root_rcp.init_ptr(nullptr);
             delete this;
         }
     }