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// Copyright (c) 2010 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 BASE_TEMPLATE_UTIL_H_
#define BASE_TEMPLATE_UTIL_H_
#pragma once
#include <cstddef> // For size_t.
#include "build/build_config.h"
namespace base {
// template definitions from tr1
template<class T, T v>
struct integral_constant {
static const T value = v;
typedef T value_type;
typedef integral_constant<T, v> type;
};
template <class T, T v> const T integral_constant<T, v>::value;
typedef integral_constant<bool, true> true_type;
typedef integral_constant<bool, false> false_type;
template <class T> struct is_pointer : false_type {};
template <class T> struct is_pointer<T*> : true_type {};
template<class> struct is_array : public false_type {};
template<class T, size_t n> struct is_array<T[n]> : public true_type {};
template<class T> struct is_array<T[]> : public true_type {};
template <class T> struct is_non_const_reference : false_type {};
template <class T> struct is_non_const_reference<T&> : true_type {};
template <class T> struct is_non_const_reference<const T&> : false_type {};
namespace internal {
// Types YesType and NoType are guaranteed such that sizeof(YesType) <
// sizeof(NoType).
typedef char YesType;
struct NoType {
YesType dummy[2];
};
// This class is an implementation detail for is_convertible, and you
// don't need to know how it works to use is_convertible. For those
// who care: we declare two different functions, one whose argument is
// of type To and one with a variadic argument list. We give them
// return types of different size, so we can use sizeof to trick the
// compiler into telling us which function it would have chosen if we
// had called it with an argument of type From. See Alexandrescu's
// _Modern C++ Design_ for more details on this sort of trick.
struct ConvertHelper {
template <typename To>
static YesType Test(To);
template <typename To>
static NoType Test(...);
template <typename From>
static From Create();
};
// Used to determine if a type is a struct/union/class. Inspired by Boost's
// is_class type_trait implementation.
struct IsClassHelper {
template <typename C>
static YesType Test(void(C::*)(void));
template <typename C>
static NoType Test(...);
};
} // namespace internal
// Inherits from true_type if From is convertible to To, false_type otherwise.
//
// Note that if the type is convertible, this will be a true_type REGARDLESS
// of whether or not the conversion would emit a warning.
template <typename From, typename To>
struct is_convertible
: integral_constant<bool,
sizeof(internal::ConvertHelper::Test<To>(
internal::ConvertHelper::Create<From>())) ==
sizeof(internal::YesType)> {
};
template <typename T>
struct is_class
: integral_constant<bool,
sizeof(internal::IsClassHelper::Test<T>(0)) ==
sizeof(internal::YesType)> {
};
} // namespace base
#endif // BASE_TEMPLATE_UTIL_H_
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