michael@0: // Copyright (c) 2011 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #ifndef BASE_TEMPLATE_UTIL_H_
michael@0: #define BASE_TEMPLATE_UTIL_H_
michael@0: 
michael@0: #include <cstddef>  // For size_t.
michael@0: 
michael@0: #include "build/build_config.h"
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: // template definitions from tr1
michael@0: 
michael@0: template<class T, T v>
michael@0: struct integral_constant {
michael@0:   static const T value = v;
michael@0:   typedef T value_type;
michael@0:   typedef integral_constant<T, v> type;
michael@0: };
michael@0: 
michael@0: template <class T, T v> const T integral_constant<T, v>::value;
michael@0: 
michael@0: typedef integral_constant<bool, true> true_type;
michael@0: typedef integral_constant<bool, false> false_type;
michael@0: 
michael@0: template <class T> struct is_pointer : false_type {};
michael@0: template <class T> struct is_pointer<T*> : true_type {};
michael@0: 
michael@0: template <class T, class U> struct is_same : public false_type {};
michael@0: template <class T> struct is_same<T,T> : true_type {};
michael@0: 
michael@0: template<class> struct is_array : public false_type {};
michael@0: template<class T, size_t n> struct is_array<T[n]> : public true_type {};
michael@0: template<class T> struct is_array<T[]> : public true_type {};
michael@0: 
michael@0: template <class T> struct is_non_const_reference : false_type {};
michael@0: template <class T> struct is_non_const_reference<T&> : true_type {};
michael@0: template <class T> struct is_non_const_reference<const T&> : false_type {};
michael@0: 
michael@0: template <class T> struct is_void : false_type {};
michael@0: template <> struct is_void<void> : true_type {};
michael@0: 
michael@0: namespace internal {
michael@0: 
michael@0: // Types YesType and NoType are guaranteed such that sizeof(YesType) <
michael@0: // sizeof(NoType).
michael@0: typedef char YesType;
michael@0: 
michael@0: struct NoType {
michael@0:   YesType dummy[2];
michael@0: };
michael@0: 
michael@0: // This class is an implementation detail for is_convertible, and you
michael@0: // don't need to know how it works to use is_convertible. For those
michael@0: // who care: we declare two different functions, one whose argument is
michael@0: // of type To and one with a variadic argument list. We give them
michael@0: // return types of different size, so we can use sizeof to trick the
michael@0: // compiler into telling us which function it would have chosen if we
michael@0: // had called it with an argument of type From.  See Alexandrescu's
michael@0: // _Modern C++ Design_ for more details on this sort of trick.
michael@0: 
michael@0: struct ConvertHelper {
michael@0:   template <typename To>
michael@0:   static YesType Test(To);
michael@0: 
michael@0:   template <typename To>
michael@0:   static NoType Test(...);
michael@0: 
michael@0:   template <typename From>
michael@0:   static From& Create();
michael@0: };
michael@0: 
michael@0: // Used to determine if a type is a struct/union/class. Inspired by Boost's
michael@0: // is_class type_trait implementation.
michael@0: struct IsClassHelper {
michael@0:   template <typename C>
michael@0:   static YesType Test(void(C::*)(void));
michael@0: 
michael@0:   template <typename C>
michael@0:   static NoType Test(...);
michael@0: };
michael@0: 
michael@0: }  // namespace internal
michael@0: 
michael@0: // Inherits from true_type if From is convertible to To, false_type otherwise.
michael@0: //
michael@0: // Note that if the type is convertible, this will be a true_type REGARDLESS
michael@0: // of whether or not the conversion would emit a warning.
michael@0: template <typename From, typename To>
michael@0: struct is_convertible
michael@0:     : integral_constant<bool,
michael@0:                         sizeof(internal::ConvertHelper::Test<To>(
michael@0:                                    internal::ConvertHelper::Create<From>())) ==
michael@0:                         sizeof(internal::YesType)> {
michael@0: };
michael@0: 
michael@0: template <typename T>
michael@0: struct is_class
michael@0:     : integral_constant<bool,
michael@0:                         sizeof(internal::IsClassHelper::Test<T>(0)) ==
michael@0:                             sizeof(internal::YesType)> {
michael@0: };
michael@0: 
michael@0: }  // namespace base
michael@0: 
michael@0: #endif  // BASE_TEMPLATE_UTIL_H_