Mojo: more idiomatic C++ bindings

mojo/public/cpp/bindings/lib/template_util.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_TEMPLATE_UTIL_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_TEMPLATE_UTIL_H_
+
+namespace mojo {
+namespace internal {
+
+template<class T, T v>
+struct IntegralConstant {
+  static const T value = v;
+};
+
+template <class T, T v> const T IntegralConstant<T, v>::value;
+
+typedef IntegralConstant<bool, true> TrueType;
+typedef IntegralConstant<bool, false> FalseType;
+
+template <class T> struct IsConst : FalseType {};
+template <class T> struct IsConst<const T> : TrueType {};
+
+template<bool B, typename T = void>
+struct EnableIf {};
+
+template<typename T>
+struct EnableIf<true, T> { typedef T type; };
+
+// Types YesType and NoType are guaranteed such that sizeof(YesType) <
+// sizeof(NoType).
+typedef char YesType;
+
+struct NoType {
+  YesType dummy[2];
+};
+
+// A helper template to determine if given type is non-const move-only-type,
+// i.e. if a value of the given type should be passed via .Pass() in a
+// destructive way.
+template <typename T> struct IsMoveOnlyType {
+  template <typename U>
+  static YesType Test(const typename U::MoveOnlyTypeForCPP03*);
+
+  template <typename U>
+  static NoType Test(...);
+
+  static const bool value = sizeof(Test<T>(0)) == sizeof(YesType) &&
+                            !IsConst<T>::value;
+};
+
+template <typename T>
+typename EnableIf<!IsMoveOnlyType<T>::value, T>::type& Forward(T& t) {
+  return t;
+}
+
+template <typename T>
+typename EnableIf<IsMoveOnlyType<T>::value, T>::type Forward(T& t) {
+  return t.Pass();
+}
+
+// This goop is a trick used to implement a template that can be used to
+// determine if a given class is the base class of another given class.
+template<typename, typename> struct IsSame {
+  static bool const value = false;
+};
+template<typename A> struct IsSame<A, A> {
+  static bool const value = true;
+};
+template<typename Base, typename Derived> struct IsBaseOf {
+ private:
+  // This class doesn't work correctly with forward declarations.
+  // Because sizeof cannot be applied to incomplete types, this line prevents us
+  // from passing in forward declarations.
+  typedef char (*EnsureTypesAreComplete)[sizeof(Base) + sizeof(Derived)];
+
+  static Derived* CreateDerived();
+  static char (&Check(Base*))[1];
+  static char (&Check(...))[2];
+
+ public:
+  static bool const value = sizeof Check(CreateDerived()) == 1 &&
+                            !IsSame<Base const, void const>::value;
+};
+
+}  // namespace internal
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_TEMPLATE_UTIL_H_