Bind: Use VariadicTemplates in bind_internal.h

base/callback_tuple.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.
+
+// Helper template classes for Bind implementation.
+
+#ifndef BASE_CALLBACK_TUPLE_H_
+#define BASE_CALLBACK_TUPLE_H_
+
+namespace base {
+namespace internal {
+
+// Packs a list of types to hold them in a single type.
+template <typename... Types>
+struct TypeList {};
+
+// Used for DropTypeListItem implementation.
+template <size_t n, typename List>
+struct DropTypeListItemImpl;
+
+// Do not use enable_if and SFINAE here to avoid MSVC2013 compile failure.
+template <size_t n, typename T, typename... List>
+struct DropTypeListItemImpl<n, TypeList<T, List...>>
+    : DropTypeListItemImpl<n - 1, TypeList<List...>> {};
+
+template <typename T, typename... List>
+struct DropTypeListItemImpl<0, TypeList<T, List...>> {
+  typedef TypeList<T, List...> Type;
+};
+
+template <>
+struct DropTypeListItemImpl<0, TypeList<>> {
+  typedef TypeList<> Type;
+};
+
+// A type-level function that drops |n| list item from given TypeList.
+template <size_t n, typename List>
+using DropTypeListItem = typename DropTypeListItemImpl<n, List>::Type;
+
+// Used for ConcatTypeLists implementation.
+template <typename List1, typename List2>
+struct ConcatTypeListsImpl;
+
+template <typename... Types1, typename... Types2>
+struct ConcatTypeListsImpl<TypeList<Types1...>, TypeList<Types2...>> {
+  typedef TypeList<Types1..., Types2...> Type;
+};
+
+// A type-level function that concats two TypeLists.
+template <typename List1, typename List2>
+using ConcatTypeLists = typename ConcatTypeListsImpl<List1, List2>::Type;
+
+template <size_t n, typename List>
+struct NthTypeImpl;
+
+template <size_t n, typename T, typename... Types>
+struct NthTypeImpl<n, TypeList<T, Types...> >
+    : NthTypeImpl<n - 1, TypeList<Types...>> {

[Nico, 2014/12/08 19:58:08]

:-/

(I know that there's no better way)

+};
+
+template <typename T, typename... Types>
+struct NthTypeImpl<0, TypeList<T, Types...> > {
+  typedef T Type;
+};
+
+// A type-level function that extracts |n|th type from a TypeList.
+template <size_t n, typename List>
+using NthType = typename NthTypeImpl<n, List>::Type;
+
+// Used for MakeFunctionType implementation.
+template <typename R, typename ArgList>
+struct MakeFunctionTypeImpl;
+
+template <typename R, typename... Args>
+struct MakeFunctionTypeImpl<R, TypeList<Args...>> {
+  typedef R(Type)(Args...);
+};
+
+// A type-level function that constructs a function type that has |R| as its
+// return type and has TypeLists items as its arguments.
+template <typename R, typename ArgList>
+using MakeFunctionType = typename MakeFunctionTypeImpl<R, ArgList>::Type;
+
+// Holds a list of indexes as a single type.
+template <size_t... indexes>
+struct IndexSequence {};
+
+template <size_t n, size_t... sequence>
+struct MakeIndexSequenceImpl
+    : MakeIndexSequenceImpl<n - 1, n - 1, sequence...> {};
+
+template <size_t... sequence>
+struct MakeIndexSequenceImpl<0, sequence...> {
+  typedef IndexSequence<sequence...> Type;
+};
+
+// A type-level function that makes IndexSequence<0, 1, .., n - 1>.
+template <size_t n>
+using MakeIndexSequence = typename MakeIndexSequenceImpl<n>::Type;
+
+// Used for Tuple<> implementation.  Holds |n|th item of a Tuple<>.
+template <size_t n, typename T>
+struct IndexedTupleItem {
+  explicit IndexedTupleItem(const T& value) : value_(value) {}
+  T value_;
+};
+
+//
+// Implementation note: Unspecialized definition handles the empty case.
+template <size_t n, typename... Types>
+struct TupleBody {};
+
+// Implementation note: Handles non-empty case of Tuple construction.
+template <size_t n, typename T, typename... Types>
+struct TupleBody<n, T, Types...>
+    : IndexedTupleItem<n, T>, TupleBody<n + 1, Types...>{
+  explicit TupleBody(const T& head, const Types&... tail)
+      : IndexedTupleItem<n, T>(head), TupleBody<n + 1, Types...>(tail...) {}
+};
+
+template <typename... Types>
+using Tuple = TupleBody<0, Types...>;
+
+// Extracts |i|th item from a tuple.
+// Example:
+//   Tuple<int, std::string, void*> tuple(1, "foo", nullptr);
+//   std::string tuple_item = *GetTupleItem<1>(&tuple);
+template <size_t i, typename T>
+T* GetTupleItem(IndexedTupleItem<i, T>* item) {
+  return &item->value_;
+}
+
+template <size_t i, typename T>
+const T* GetTupleItem(const IndexedTupleItem<i, T>* item) {
+  return &item->value_;
+}
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_CALLBACK_TUPLE_H_