Add template aliases to support both reference counting and garbage collection for a transition per…

Source/wtf/Ptr.h

+/*
+ * Copyright (C) 2014 Google, Inc. All Rights Reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef WTF_Ptr_h
+#define WTF_Ptr_h
+
+// Ptr is a simple wrapper for a raw pointer that provides the
+// interface (get, clear) of other pointer types such as RefPtr,
+// Persistent and Member. This is used for the Blink garbage
+// collection work in order to be able to write shared code that will
+// use reference counting or garbage collection based on a
+// compile-time flag.
+
+namespace WTF {
+
+template<typename T>
+class Ptr {
+public:
+    Ptr(T* ptr) : m_ptr(ptr) { }
+    Ptr(std::nullptr_t) : m_ptr(0) { }
+
+    template<typename U>
+    Ptr(const Ptr<U>& other)
+        : m_ptr(other.get())
+    {
+    }
+
+    T* get() const { return m_ptr; }
+    void clear() { m_ptr = 0; }
+
+    Ptr& operator=(T* ptr)
+    {
+        m_ptr = ptr;
+        return *this;
+    }
+
+    Ptr& operator=(std::nullptr_t)
+    {
+        m_ptr = 0;
+        return *this;
+    }
+
+    operator T*() const { return m_ptr; }
+    T& operator*() const { return *m_ptr; }
+    T* operator->() const { return m_ptr; }
+    bool operator!() const { return !m_ptr; }
+
+    // This conversion operator allows implicit conversion to bool but
+    // not to other integer types.
+    typedef T* Ptr::*UnspecifiedBoolType;
+    operator UnspecifiedBoolType() const { return m_ptr ? &m_ptr : 0; }
+
+private:
+    T* m_ptr;
+};
+
+} // namespace WTF
+
+using WTF::Ptr;
+
+#endif