diff options
Diffstat (limited to 'third_party/base/template_util.h')
| -rw-r--r-- | third_party/base/template_util.h | 152 |
1 files changed, 51 insertions, 101 deletions
diff --git a/third_party/base/template_util.h b/third_party/base/template_util.h index 0fed0cc259..8544aa2945 100644 --- a/third_party/base/template_util.h +++ b/third_party/base/template_util.h @@ -7,22 +7,13 @@ #include <stddef.h> #include <iosfwd> +#include <iterator> #include <type_traits> #include <utility> +#include <vector> #include "build/build_config.h" -// This hacks around libstdc++ 4.6 missing stuff in type_traits, while we need -// to support it. -#define CR_GLIBCXX_4_7_0 20120322 -#define CR_GLIBCXX_4_5_4 20120702 -#define CR_GLIBCXX_4_6_4 20121127 -#if defined(__GLIBCXX__) && \ - (__GLIBCXX__ < CR_GLIBCXX_4_7_0 || __GLIBCXX__ == CR_GLIBCXX_4_5_4 || \ - __GLIBCXX__ == CR_GLIBCXX_4_6_4) -#define CR_USE_FALLBACKS_FOR_OLD_GLIBCXX -#endif - // 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 @@ -47,52 +38,30 @@ 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 {}; - -// is_assignable +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 { -template <typename First, typename Second> -struct SelectSecond { - using type = Second; +// Implementation detail of base::void_t below. +template <typename...> +struct make_void { + using type = void; }; -struct Any { - Any(...); -}; +} // namespace internal -// True case: If |Lvalue| can be assigned to from |Rvalue|, then the return -// value is a true_type. -template <class Lvalue, class Rvalue> -typename internal::SelectSecond< - decltype((std::declval<Lvalue>() = std::declval<Rvalue>())), - std::true_type>::type -IsAssignableTest(Lvalue&&, Rvalue&&); - -// False case: Otherwise the return value is a false_type. -template <class Rvalue> -std::false_type IsAssignableTest(internal::Any, Rvalue&&); - -// Default case: Neither Lvalue nor Rvalue is void. Uses IsAssignableTest to -// determine the type of IsAssignableImpl. -template <class Lvalue, - class Rvalue, - bool = std::is_void<Lvalue>::value || std::is_void<Rvalue>::value> -struct IsAssignableImpl - : public std::common_type<decltype( - internal::IsAssignableTest(std::declval<Lvalue>(), - std::declval<Rvalue>()))>::type {}; - -// Void case: Either Lvalue or Rvalue is void. Then the type of IsAssignableTest -// is false_type. -template <class Lvalue, class Rvalue> -struct IsAssignableImpl<Lvalue, Rvalue, true> : public std::false_type {}; +// 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: +// http://en.cppreference.com/w/cpp/types/void_t +// http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1558 +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> @@ -103,58 +72,23 @@ struct SupportsOstreamOperator<T, << std::declval<T>()))> : std::true_type {}; -} // namespace internal - -// TODO(crbug.com/554293): Remove this when all platforms have this in the std -// namespace. -template <class Lvalue, class Rvalue> -struct is_assignable : public internal::IsAssignableImpl<Lvalue, Rvalue> {}; - -// is_copy_assignable is true if a T const& is assignable to a T&. -// TODO(crbug.com/554293): Remove this when all platforms have this in the std -// namespace. -template <class T> -struct is_copy_assignable - : public is_assignable<typename std::add_lvalue_reference<T>::type, - typename std::add_lvalue_reference< - typename std::add_const<T>::type>::type> {}; - -// is_move_assignable is true if a T&& is assignable to a T&. -// TODO(crbug.com/554293): Remove this when all platforms have this in the std -// namespace. -template <class T> -struct is_move_assignable - : public is_assignable<typename std::add_lvalue_reference<T>::type, - const typename std::add_rvalue_reference<T>::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 {}; -// underlying_type produces the integer type backing an enum type. -// TODO(crbug.com/554293): Remove this when all platforms have this in the std -// namespace. -#if defined(CR_USE_FALLBACKS_FOR_OLD_GLIBCXX) -template <typename T> -struct underlying_type { - using type = __underlying_type(T); -}; -#else template <typename T> -using underlying_type = std::underlying_type<T>; -#endif +struct is_iterator<T, + void_t<typename std::iterator_traits<T>::iterator_category>> + : std::true_type {}; -// TODO(crbug.com/554293): Remove this when all platforms have this in the std -// namespace. -#if defined(CR_USE_FALLBACKS_FOR_OLD_GLIBCXX) -template <class T> -using is_trivially_destructible = std::has_trivial_destructor<T>; -#else -template <class T> -using is_trivially_destructible = std::is_trivially_destructible<T>; -#endif +} // 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. In this case we should provide it based on compiler -// intrinsics. This is covered by the CR_USE_FALLBACKS_FOR_OLD_GLIBCXX define. +// 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 // case, which is covered by CR_USE_FALLBACKS_FOR_OLD_EXPERIMENTAL_GLIBCXX. @@ -175,8 +109,7 @@ using is_trivially_destructible = std::is_trivially_destructible<T>; // TODO(crbug.com/554293): Remove this when all platforms have this in the std // namespace and it works with gcc as needed. -#if defined(CR_USE_FALLBACKS_FOR_OLD_GLIBCXX) || \ - defined(CR_USE_FALLBACKS_FOR_OLD_EXPERIMENTAL_GLIBCXX) || \ +#if defined(CR_USE_FALLBACKS_FOR_OLD_EXPERIMENTAL_GLIBCXX) || \ defined(CR_USE_FALLBACKS_FOR_GCC_WITH_LIBCXX) template <typename T> struct is_trivially_copyable { @@ -186,7 +119,8 @@ struct is_trivially_copyable { #if _GNUC_VER >= 501 static constexpr bool value = __is_trivially_copyable(T); #else - static constexpr bool value = __has_trivial_copy(T); + static constexpr bool value = + __has_trivial_copy(T) && __has_trivial_destructor(T); #endif }; #else @@ -194,9 +128,25 @@ template <class T> using is_trivially_copyable = std::is_trivially_copyable<T>; #endif +#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ <= 7 +// Workaround for g++7 and earlier family. +// Due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80654, 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 {}; +#else +// Otherwise use std::is_trivially_copy_constructible as is. +template <typename T> +using is_trivially_copy_constructible = std::is_trivially_copy_constructible<T>; +#endif + } // namespace base -#undef CR_USE_FALLBACKS_FOR_OLD_GLIBCXX #undef CR_USE_FALLBACKS_FOR_GCC_WITH_LIBCXX #undef CR_USE_FALLBACKS_FOR_OLD_EXPERIMENTAL_GLIBCXX |