Add initial idea for API

include/rcp.h

@@ -0,0 +1,123 @@
+#pragma once
+
+#include <atomic>
+
+namespace rcp_internal
+{
+    class root
+    {
+    private:
+        mutable std::atomic<int> ref_count{0};
+
+        rcp<root> root_rcp;
+
+    protected:
+        root()
+        {
+            root_rcp = rcp<root>(this);
+        }
+
+        virtual ~root() = default;
+
+    public:
+        void add_ref() const
+        {
+            ref_count.fetch_add(1, std::memory_order_relaxed);
+        }
+
+        void release_ref() const
+        {
+            if (ref_count.fetch_sub(1, std::memory_order_acq_rel) == 0)
+            {
+                delete this;
+            }
+        }
+
+        rcp<root> & get_root_rcp()
+        {
+            return root_rcp;
+        }
+    }
+
+    template <typename T>
+    class managed
+    {
+    public:
+        static_assert(std::is_base_of<root, T>::value,
+                "T must inherit from rcp::root to use rcp::managed<T>");
+
+        rcp<T> get_rcp()
+        {
+            root * r = (root *)this;
+            return rcp<T>(r->get_root_ref());
+        }
+    }
+}
+
+/**
+ * Reference-counting pointer.
+ */
+template <typename T>
+class rcp
+{
+private:
+    T * ptr = nullptr;
+
+    explicit rcp(T * p) : ptr(p)
+    {
+        if (p)
+        {
+            ptr->add_ref();
+        }
+    }
+
+    friend T;
+
+public:
+    rcp() = default;
+
+    rcp(const rcp & other) : ptr(other.ptr)
+    {
+        if (ptr)
+        {
+            ptr->add_ref();
+        }
+    }
+
+    ~rcp()
+    {
+        if (ptr)
+        {
+            ptr->release_ref();
+        }
+    }
+
+    /* Casting constructor: allows rcp<Base> -> rcp<Derived> */
+    template <typename U>
+    rcp(const rcp<U> & other) : ptr(static_cast<T *>(other.get_raw()))
+    {
+        if (ptr)
+        {
+            ptr->add_ref();
+        }
+    }
+
+    T * get_raw() const
+    {
+        return ptr;
+    }
+
+    T * operator->() const
+    {
+        return ptr;
+    }
+
+    bool operator!() const
+    {
+        return !ptr;
+    }
+
+    using root = rcp_internal::root;
+
+    using managed = rcp_internal::managed;
+}