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115 lines
3.6 KiB
C++
115 lines
3.6 KiB
C++
/*
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* Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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// Borrowed from Chromium's src/base/template_util.h.
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#ifndef WEBRTC_SYSTEM_WRAPPERS_INTERFACE_TEMPLATE_UTIL_H_
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#define WEBRTC_SYSTEM_WRAPPERS_INTERFACE_TEMPLATE_UTIL_H_
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#include <stddef.h> // For size_t.
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namespace webrtc {
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// Template definitions from tr1.
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template<class T, T v>
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struct integral_constant {
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static const T value = v;
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typedef T value_type;
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typedef integral_constant<T, v> type;
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};
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template <class T, T v> const T integral_constant<T, v>::value;
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typedef integral_constant<bool, true> true_type;
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typedef integral_constant<bool, false> false_type;
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template <class T> struct is_pointer : false_type {};
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template <class T> struct is_pointer<T*> : true_type {};
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template <class T, class U> struct is_same : public false_type {};
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template <class T> struct is_same<T, T> : true_type {};
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template<class> struct is_array : public false_type {};
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template<class T, size_t n> struct is_array<T[n]> : public true_type {};
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template<class T> struct is_array<T[]> : public true_type {};
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template <class T> struct is_non_const_reference : false_type {};
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template <class T> struct is_non_const_reference<T&> : true_type {};
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template <class T> struct is_non_const_reference<const T&> : false_type {};
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template <class T> struct is_void : false_type {};
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template <> struct is_void<void> : true_type {};
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namespace internal {
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// Types YesType and NoType are guaranteed such that sizeof(YesType) <
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// sizeof(NoType).
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typedef char YesType;
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struct NoType {
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YesType dummy[2];
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};
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// This class is an implementation detail for is_convertible, and you
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// don't need to know how it works to use is_convertible. For those
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// who care: we declare two different functions, one whose argument is
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// of type To and one with a variadic argument list. We give them
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// return types of different size, so we can use sizeof to trick the
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// compiler into telling us which function it would have chosen if we
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// had called it with an argument of type From. See Alexandrescu's
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// _Modern C++ Design_ for more details on this sort of trick.
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struct ConvertHelper {
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template <typename To>
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static YesType Test(To);
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template <typename To>
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static NoType Test(...);
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template <typename From>
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static From& Create();
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};
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// Used to determine if a type is a struct/union/class. Inspired by Boost's
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// is_class type_trait implementation.
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struct IsClassHelper {
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template <typename C>
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static YesType Test(void(C::*)(void));
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template <typename C>
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static NoType Test(...);
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};
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} // namespace internal
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// Inherits from true_type if From is convertible to To, false_type otherwise.
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//
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// Note that if the type is convertible, this will be a true_type REGARDLESS
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// of whether or not the conversion would emit a warning.
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template <typename From, typename To>
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struct is_convertible
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: integral_constant<bool,
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sizeof(internal::ConvertHelper::Test<To>(
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internal::ConvertHelper::Create<From>())) ==
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sizeof(internal::YesType)> {
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};
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template <typename T>
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struct is_class
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: integral_constant<bool,
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sizeof(internal::IsClassHelper::Test<T>(0)) ==
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sizeof(internal::YesType)> {
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};
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} // namespace webrtc
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#endif // WEBRTC_SYSTEM_WRAPPERS_INTERFACE_TEMPLATE_UTIL_H_
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