AK: Rename Retainable.h => RefCounted.h.

AK/RefCounted.h

@@ -0,0 +1,78 @@
+#pragma once
+
+#include "Assertions.h"
+#include "StdLibExtras.h"
+
+namespace AK {
+
+template<class T>
+constexpr auto call_will_be_destroyed_if_present(T* object) -> decltype(object->will_be_destroyed(), TrueType {})
+{
+    object->will_be_destroyed();
+    return {};
+}
+
+constexpr auto call_will_be_destroyed_if_present(...) -> FalseType
+{
+    return {};
+}
+
+template<class T>
+constexpr auto call_one_ref_left_if_present(T* object) -> decltype(object->one_ref_left(), TrueType {})
+{
+    object->one_ref_left();
+    return {};
+}
+
+constexpr auto call_one_ref_left_if_present(...) -> FalseType
+{
+    return {};
+}
+
+class RefCountedBase {
+public:
+    void ref()
+    {
+        ASSERT(m_ref_count);
+        ++m_ref_count;
+    }
+
+    int ref_count() const
+    {
+        return m_ref_count;
+    }
+
+protected:
+    RefCountedBase() {}
+    ~RefCountedBase()
+    {
+        ASSERT(!m_ref_count);
+    }
+
+    void deref_base()
+    {
+        ASSERT(m_ref_count);
+        --m_ref_count;
+    }
+
+    int m_ref_count { 1 };
+};
+
+template<typename T>
+class RefCounted : public RefCountedBase {
+public:
+    void deref()
+    {
+        deref_base();
+        if (m_ref_count == 0) {
+            call_will_be_destroyed_if_present(static_cast<T*>(this));
+            delete static_cast<T*>(this);
+        } else if (m_ref_count == 1) {
+            call_one_ref_left_if_present(static_cast<T*>(this));
+        }
+    }
+};
+
+}
+
+using AK::RefCounted;