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Remove the polyfill implementations for many type traits and alias
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them to their std equivalents. It is recommended that clients now
simple use the std equivalents.

PiperOrigin-RevId: 731931492
Change-Id: I1f204dd659f12c4d9cc183f230ce13052a523625
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@derekmauro @copybara-github
derekmauro authored and copybara-github committed Feb 28, 2025
1 parent b22423e commit f1b7d00
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Showing 2 changed files with 27 additions and 587 deletions.
187 changes: 27 additions & 160 deletions absl/meta/type_traits.h
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Original file line number Diff line number Diff line change
Expand Up @@ -97,22 +97,6 @@ struct is_detected_impl<typename VoidTImpl<Op<Args...>>::type, Op, Args...> {
template <template <class...> class Op, class... Args>
struct is_detected : is_detected_impl<void, Op, Args...>::type {};

template <class Enabler, class To, template <class...> class Op, class... Args>
struct is_detected_convertible_impl {
using type = std::false_type;
};

template <class To, template <class...> class Op, class... Args>
struct is_detected_convertible_impl<
typename std::enable_if<std::is_convertible<Op<Args...>, To>::value>::type,
To, Op, Args...> {
using type = std::true_type;
};

template <class To, template <class...> class Op, class... Args>
struct is_detected_convertible
: is_detected_convertible_impl<void, To, Op, Args...>::type {};

} // namespace type_traits_internal

// void_t()
Expand All @@ -121,103 +105,50 @@ struct is_detected_convertible
// metafunction allows you to create a general case that maps to `void` while
// allowing specializations that map to specific types.
//
// This metafunction is designed to be a drop-in replacement for the C++17
// `std::void_t` metafunction.
//
// NOTE: `absl::void_t` does not use the standard-specified implementation so
// that it can remain compatible with gcc < 5.1. This can introduce slightly
// different behavior, such as when ordering partial specializations.
// This metafunction is not 100% compatible with the C++17 `std::void_t`
// metafunction. It has slightly different behavior, such as when ordering
// partial specializations. It is recommended to use `std::void_t` instead.
template <typename... Ts>
using void_t = typename type_traits_internal::VoidTImpl<Ts...>::type;

// conjunction
//
// Performs a compile-time logical AND operation on the passed types (which
// must have `::value` members convertible to `bool`. Short-circuits if it
// encounters any `false` members (and does not compare the `::value` members
// of any remaining arguments).
//
// This metafunction is designed to be a drop-in replacement for the C++17
// `std::conjunction` metafunction.
template <typename... Ts>
struct conjunction : std::true_type {};

template <typename T, typename... Ts>
struct conjunction<T, Ts...>
: std::conditional<T::value, conjunction<Ts...>, T>::type {};

template <typename T>
struct conjunction<T> : T {};

// disjunction
//
// Performs a compile-time logical OR operation on the passed types (which
// must have `::value` members convertible to `bool`. Short-circuits if it
// encounters any `true` members (and does not compare the `::value` members
// of any remaining arguments).
//
// This metafunction is designed to be a drop-in replacement for the C++17
// `std::disjunction` metafunction.
template <typename... Ts>
struct disjunction : std::false_type {};

template <typename T, typename... Ts>
struct disjunction<T, Ts...>
: std::conditional<T::value, T, disjunction<Ts...>>::type {};

template <typename T>
struct disjunction<T> : T {};

// negation
//
// Performs a compile-time logical NOT operation on the passed type (which
// must have `::value` members convertible to `bool`.
//
// This metafunction is designed to be a drop-in replacement for the C++17
// `std::negation` metafunction.
template <typename T>
struct negation : std::integral_constant<bool, !T::value> {};

// is_function()
//
// Determines whether the passed type `T` is a function type.
//
// This metafunction is designed to be a drop-in replacement for the C++11
// `std::is_function()` metafunction for platforms that have incomplete C++11
// support (such as libstdc++ 4.x).
//
// This metafunction works because appending `const` to a type does nothing to
// function types and reference types (and forms a const-qualified type
// otherwise).
template <typename T>
struct is_function
: std::integral_constant<
bool, !(std::is_reference<T>::value ||
std::is_const<typename std::add_const<T>::type>::value)> {};

// is_copy_assignable()
// is_move_assignable()
// is_trivially_destructible()
// is_trivially_default_constructible()
// is_trivially_move_constructible()
// is_trivially_copy_constructible()
// is_trivially_move_assignable()
// is_trivially_copy_assignable()
//
// Historical note: Abseil once provided implementations of these type traits
// for platforms that lacked full support. New code should prefer to use the
// std variants.
//
// See the documentation for the STL <type_traits> header for more information:
// https://en.cppreference.com/w/cpp/header/type_traits
using std::add_const_t;
using std::add_cv_t;
using std::add_lvalue_reference_t;
using std::add_pointer_t;
using std::add_rvalue_reference_t;
using std::add_volatile_t;
using std::common_type_t;
using std::conditional_t;
using std::conjunction;
using std::decay_t;
using std::enable_if_t;
using std::disjunction;
using std::is_copy_assignable;
using std::is_function;
using std::is_move_assignable;
using std::is_trivially_copy_assignable;
using std::is_trivially_copy_constructible;
using std::is_trivially_default_constructible;
using std::is_trivially_destructible;
using std::is_trivially_move_assignable;
using std::is_trivially_move_constructible;
using std::make_signed_t;
using std::make_unsigned_t;
using std::negation;
using std::remove_all_extents_t;
using std::remove_const_t;
using std::remove_cv_t;
using std::remove_extent_t;
using std::remove_pointer_t;
using std::remove_reference_t;
using std::remove_volatile_t;
using std::underlying_type_t;

#if defined(__cpp_lib_remove_cvref) && __cpp_lib_remove_cvref >= 201711L
template <typename T>
Expand All @@ -240,70 +171,6 @@ template <typename T>
using remove_cvref_t = typename remove_cvref<T>::type;
#endif

// -----------------------------------------------------------------------------
// C++14 "_t" trait aliases
// -----------------------------------------------------------------------------

template <typename T>
using remove_cv_t = typename std::remove_cv<T>::type;

template <typename T>
using remove_const_t = typename std::remove_const<T>::type;

template <typename T>
using remove_volatile_t = typename std::remove_volatile<T>::type;

template <typename T>
using add_cv_t = typename std::add_cv<T>::type;

template <typename T>
using add_const_t = typename std::add_const<T>::type;

template <typename T>
using add_volatile_t = typename std::add_volatile<T>::type;

template <typename T>
using remove_reference_t = typename std::remove_reference<T>::type;

template <typename T>
using add_lvalue_reference_t = typename std::add_lvalue_reference<T>::type;

template <typename T>
using add_rvalue_reference_t = typename std::add_rvalue_reference<T>::type;

template <typename T>
using remove_pointer_t = typename std::remove_pointer<T>::type;

template <typename T>
using add_pointer_t = typename std::add_pointer<T>::type;

template <typename T>
using make_signed_t = typename std::make_signed<T>::type;

template <typename T>
using make_unsigned_t = typename std::make_unsigned<T>::type;

template <typename T>
using remove_extent_t = typename std::remove_extent<T>::type;

template <typename T>
using remove_all_extents_t = typename std::remove_all_extents<T>::type;

template <typename T>
using decay_t = typename std::decay<T>::type;

template <bool B, typename T = void>
using enable_if_t = typename std::enable_if<B, T>::type;

template <bool B, typename T, typename F>
using conditional_t = typename std::conditional<B, T, F>::type;

template <typename... T>
using common_type_t = typename std::common_type<T...>::type;

template <typename T>
using underlying_type_t = typename std::underlying_type<T>::type;

namespace type_traits_internal {

#if (defined(__cpp_lib_is_invocable) && __cpp_lib_is_invocable >= 201703L) || \
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