Enable getting scoped_ptr type from v8 value.

God damned C++ template.

common/swap_or_assign.h

@@ -0,0 +1,41 @@
+// Copyright (c) 2013 GitHub, Inc. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ATOM_COMMON_SWAP_OR_ASSIGN_H_
+#define ATOM_COMMON_SWAP_OR_ASSIGN_H_
+
+namespace internal {
+
+// Helper to detect whether value has specified method.
+template <typename T>
+class HasSwapMethod {
+  typedef char one;
+  typedef long two;
+  template <typename C> static one test(char[sizeof(&C::swap)]) ;
+  template <typename C> static two test(...);
+ public:
+  enum { value = sizeof(test<T>(0)) == sizeof(char) };
+};
+
+template<bool B, class T = void>
+struct enable_if {};
+
+template<class T>
+struct enable_if<true, T> { typedef T type; };
+
+template<typename T>
+typename enable_if<HasSwapMethod<T>::value>::type SwapOrAssign(
+    T& v1, const T& v2) {
+  v1.swap(const_cast<T&>(v2));
+}
+
+template<typename T>
+typename enable_if<!HasSwapMethod<T>::value>::type SwapOrAssign(
+    T& v1, const T& v2) {
+  v1 = v2;
+}
+
+}  // namespace internal
+
+#endif  // ATOM_COMMON_SWAP_OR_ASSIGN_H_