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* Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
// Borrowed from Chromium's src/base/template_util.h.
#include <stddef.h> // For size_t.
namespace rtc {
// 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 T, class U>
struct is_same : public false_type {};
template <class T>
struct is_same<T, 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 {};
template <class T>
struct is_void : false_type {};
template <>
struct is_void<void> : true_type {};
// Helper useful for converting a tuple to variadic template function
// arguments.
// sequence_generator<3>::type will be sequence<0, 1, 2>.
template <int...>
struct sequence {};
template <int N, int... S>
struct sequence_generator : sequence_generator<N - 1, N - 1, S...> {};
template <int... S>
struct sequence_generator<0, S...> {
typedef sequence<S...> 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,
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 rtc