blob: 8544aa294597cc16b4c0da17ce0ab098a99a4e98 [file] [log] [blame]
// Copyright (c) 2011 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.
#include <stddef.h>
#include <iosfwd>
#include <iterator>
#include <type_traits>
#include <utility>
#include <vector>
#include "build/build_config.h"
// Some versions of libstdc++ have partial support for type_traits, but misses
// a smaller subset while removing some of the older non-standard stuff. Assume
// that all versions below 5.0 fall in this category, along with one 5.0
// experimental release. Test for this by consulting compiler major version,
// the only reliable option available, so theoretically this could fail should
// you attempt to mix an earlier version of libstdc++ with >= GCC5. But
// that's unlikely to work out, especially as GCC5 changed ABI.
#define CR_GLIBCXX_5_0_0 20150123
#if (defined(__GNUC__) && __GNUC__ < 5) || \
(defined(__GLIBCXX__) && __GLIBCXX__ == CR_GLIBCXX_5_0_0)
// This hacks around using gcc with libc++ which has some incompatibilies.
// - is_trivially_* doesn't work:
// TODO(danakj): Remove this when android builders are all using a newer version
// of gcc, or the android ndk is updated to a newer libc++ that works with older
// gcc versions.
#if !defined(__clang__) && defined(_LIBCPP_VERSION)
namespace base {
template <class T> struct is_non_const_reference : std::false_type {};
template <class T> struct is_non_const_reference<T&> : std::true_type {};
template <class T> struct is_non_const_reference<const T&> : std::false_type {};
namespace internal {
// Implementation detail of base::void_t below.
template <typename...>
struct make_void {
using type = void;
} // namespace internal
// base::void_t is an implementation of std::void_t from C++17.
// We use |base::internal::make_void| as a helper struct to avoid a C++14
// defect:
template <typename... Ts>
using void_t = typename ::base::internal::make_void<Ts...>::type;
namespace internal {
// Uses expression SFINAE to detect whether using operator<< would work.
template <typename T, typename = void>
struct SupportsOstreamOperator : std::false_type {};
template <typename T>
struct SupportsOstreamOperator<T,
<< std::declval<T>()))>
: std::true_type {};
// Used to detech whether the given type is an iterator. This is normally used
// with std::enable_if to provide disambiguation for functions that take
// templatzed iterators as input.
template <typename T, typename = void>
struct is_iterator : std::false_type {};
template <typename T>
struct is_iterator<T,
void_t<typename std::iterator_traits<T>::iterator_category>>
: std::true_type {};
} // namespace internal
// is_trivially_copyable is especially hard to get right.
// - Older versions of libstdc++ will fail to have it like they do for other
// type traits. This has become a subset of the second point, but used to be
// handled independently.
// - An experimental release of gcc includes most of type_traits but misses
// is_trivially_copyable, so we still have to avoid using libstdc++ in this
// - When compiling libc++ from before r239653, with a gcc compiler, the
// std::is_trivially_copyable can fail. So we need to work around that by not
// using the one in libc++ in this case. This is covered by the
// CR_USE_FALLBACKS_FOR_GCC_WITH_LIBCXX define, and is discussed in
// where they point out that
// in libc++'s commit r239653 this is fixed by libc++ checking for gcc 5.1.
// - In both of the above cases we are using the gcc compiler. When defining
// this ourselves on compiler intrinsics, the __is_trivially_copyable()
// intrinsic is not available on gcc before version 5.1 (see the discussion in
// again), so we must check for
// that version.
// - When __is_trivially_copyable() is not available because we are on gcc older
// than 5.1, we need to fall back to something, so we use __has_trivial_copy()
// instead based on what was done one-off in bit_cast() previously.
// TODO( Remove this when all platforms have this in the std
// namespace and it works with gcc as needed.
template <typename T>
struct is_trivially_copyable {
// TODO(danakj): Remove this when android builders are all using a newer version
// of gcc, or the android ndk is updated to a newer libc++ that does this for
// us.
#if _GNUC_VER >= 501
static constexpr bool value = __is_trivially_copyable(T);
static constexpr bool value =
__has_trivial_copy(T) && __has_trivial_destructor(T);
template <class T>
using is_trivially_copyable = std::is_trivially_copyable<T>;
#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ <= 7
// Workaround for g++7 and earlier family.
// Due to, without this
// Optional<std::vector<T>> where T is non-copyable causes a compile error.
// As we know it is not trivially copy constructible, explicitly declare so.
template <typename T>
struct is_trivially_copy_constructible
: std::is_trivially_copy_constructible<T> {};
template <typename... T>
struct is_trivially_copy_constructible<std::vector<T...>> : std::false_type {};
// Otherwise use std::is_trivially_copy_constructible as is.
template <typename T>
using is_trivially_copy_constructible = std::is_trivially_copy_constructible<T>;
} // namespace base