Add WeakPtr/Weakable templates.

AK/WeakPtr.h

@@ -0,0 +1,37 @@
+#pragma once
+
+#include "Weakable.h"
+
+namespace AK {
+
+template<typename T>
+class WeakPtr {
+    friend class Weakable<T>;
+public:
+    WeakPtr() { }
+    WeakPtr(std::nullptr_t) { }
+
+    operator bool() const { return ptr(); }
+
+    T* ptr() { return m_link ? m_link->ptr() : nullptr; }
+    const T* ptr() const { return m_link ? m_link->ptr() : nullptr; }
+    bool isNull() const { return !m_link || !m_link->ptr(); }
+
+private:
+    WeakPtr(RetainPtr<WeakLink<T>>&& link) : m_link(std::move(link)) { }
+
+    RetainPtr<WeakLink<T>> m_link;
+};
+
+template<typename T>
+inline WeakPtr<T> Weakable<T>::makeWeakPtr()
+{
+    if (!m_link)
+        m_link = adopt(*new WeakLink<T>(*this));
+    return WeakPtr<T>(m_link.copyRef());
+}
+
+}
+
+using AK::WeakPtr;
+