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// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// compare.h
// -----------------------------------------------------------------------------
//
// This header file defines the `absl::partial_ordering`, `absl::weak_ordering`,
// and `absl::strong_ordering` types for storing the results of three way
// comparisons.
//
// Example:
// absl::weak_ordering compare(const std::string& a, const std::string& b);
//
// These are C++11 compatible versions of the C++20 corresponding types
// (`std::partial_ordering`, etc.) and are designed to be drop-in replacements
// for code compliant with C++20.
#ifndef ABSL_TYPES_COMPARE_H_
#define ABSL_TYPES_COMPARE_H_
#include "absl/base/config.h"
#ifdef ABSL_USES_STD_ORDERING
#include <compare> // IWYU pragma: export
#include <type_traits>
#include "absl/meta/type_traits.h"
#else
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <type_traits>
#include "absl/base/attributes.h"
#include "absl/base/macros.h"
#include "absl/meta/type_traits.h"
#endif
namespace absl {
ABSL_NAMESPACE_BEGIN
#ifdef ABSL_USES_STD_ORDERING
using std::partial_ordering;
using std::strong_ordering;
using std::weak_ordering;
#else
namespace compare_internal {
using value_type = int8_t;
class OnlyLiteralZero {
public:
#if ABSL_HAVE_ATTRIBUTE(enable_if)
// On clang, we can avoid triggering modernize-use-nullptr by only enabling
// this overload when the value is a compile time integer constant equal to 0.
//
// In c++20, this could be a static_assert in a consteval function.
constexpr OnlyLiteralZero(int n) // NOLINT
__attribute__((enable_if(n == 0, "Only literal `0` is allowed."))) {}
#else // ABSL_HAVE_ATTRIBUTE(enable_if)
// Accept only literal zero since it can be implicitly converted to a pointer
// to member type. nullptr constants will be caught by the other constructor
// which accepts a nullptr_t.
//
// This constructor is not used for clang since it triggers
// modernize-use-nullptr.
constexpr OnlyLiteralZero(int OnlyLiteralZero::*) noexcept {} // NOLINT
#endif
// Fails compilation when `nullptr` or integral type arguments other than
// `int` are passed. This constructor doesn't accept `int` because literal `0`
// has type `int`. Literal `0` arguments will be implicitly converted to
// `std::nullptr_t` and accepted by the above constructor, while other `int`
// arguments will fail to be converted and cause compilation failure.
template <typename T, typename = typename std::enable_if<
std::is_same<T, std::nullptr_t>::value ||
(std::is_integral<T>::value &&
!std::is_same<T, int>::value)>::type>
OnlyLiteralZero(T) { // NOLINT
static_assert(sizeof(T) < 0, "Only literal `0` is allowed.");
}
};
enum class eq : value_type {
equal = 0,
equivalent = equal,
nonequal = 1,
nonequivalent = nonequal,
};
enum class ord : value_type { less = -1, greater = 1 };
enum class ncmp : value_type { unordered = -127 };
// Define macros to allow for creation or emulation of C++17 inline variables
// based on whether the feature is supported. Note: we can't use
// ABSL_INTERNAL_INLINE_CONSTEXPR here because the variables here are of
// incomplete types so they need to be defined after the types are complete.
#ifdef __cpp_inline_variables
// A no-op expansion that can be followed by a semicolon at class level.
#define ABSL_COMPARE_INLINE_BASECLASS_DECL(name) static_assert(true, "")
#define ABSL_COMPARE_INLINE_SUBCLASS_DECL(type, name) \
static const type name
#define ABSL_COMPARE_INLINE_INIT(type, name, init) \
inline constexpr type type::name(init)
#else // __cpp_inline_variables
#define ABSL_COMPARE_INLINE_BASECLASS_DECL(name) \
ABSL_CONST_INIT static const T name
// A no-op expansion that can be followed by a semicolon at class level.
#define ABSL_COMPARE_INLINE_SUBCLASS_DECL(type, name) static_assert(true, "")
#define ABSL_COMPARE_INLINE_INIT(type, name, init) \
template <typename T> \
const T compare_internal::type##_base<T>::name(init)
#endif // __cpp_inline_variables
// These template base classes allow for defining the values of the constants
// in the header file (for performance) without using inline variables (which
// aren't available in C++11).
template <typename T>
struct partial_ordering_base {
ABSL_COMPARE_INLINE_BASECLASS_DECL(less);
ABSL_COMPARE_INLINE_BASECLASS_DECL(equivalent);
ABSL_COMPARE_INLINE_BASECLASS_DECL(greater);
ABSL_COMPARE_INLINE_BASECLASS_DECL(unordered);
};
template <typename T>
struct weak_ordering_base {
ABSL_COMPARE_INLINE_BASECLASS_DECL(less);
ABSL_COMPARE_INLINE_BASECLASS_DECL(equivalent);
ABSL_COMPARE_INLINE_BASECLASS_DECL(greater);
};
template <typename T>
struct strong_ordering_base {
ABSL_COMPARE_INLINE_BASECLASS_DECL(less);
ABSL_COMPARE_INLINE_BASECLASS_DECL(equal);
ABSL_COMPARE_INLINE_BASECLASS_DECL(equivalent);
ABSL_COMPARE_INLINE_BASECLASS_DECL(greater);
};
} // namespace compare_internal
class partial_ordering
: public compare_internal::partial_ordering_base<partial_ordering> {
explicit constexpr partial_ordering(compare_internal::eq v) noexcept
: value_(static_cast<compare_internal::value_type>(v)) {}
explicit constexpr partial_ordering(compare_internal::ord v) noexcept
: value_(static_cast<compare_internal::value_type>(v)) {}
explicit constexpr partial_ordering(compare_internal::ncmp v) noexcept
: value_(static_cast<compare_internal::value_type>(v)) {}
friend struct compare_internal::partial_ordering_base<partial_ordering>;
constexpr bool is_ordered() const noexcept {
return value_ !=
compare_internal::value_type(compare_internal::ncmp::unordered);
}
public:
ABSL_COMPARE_INLINE_SUBCLASS_DECL(partial_ordering, less);
ABSL_COMPARE_INLINE_SUBCLASS_DECL(partial_ordering, equivalent);
ABSL_COMPARE_INLINE_SUBCLASS_DECL(partial_ordering, greater);
ABSL_COMPARE_INLINE_SUBCLASS_DECL(partial_ordering, unordered);
// Comparisons
friend constexpr bool operator==(
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ == 0;
}
friend constexpr bool operator!=(
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return !v.is_ordered() || v.value_ != 0;
}
friend constexpr bool operator<(
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ < 0;
}
friend constexpr bool operator<=(
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ <= 0;
}
friend constexpr bool operator>(
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ > 0;
}
friend constexpr bool operator>=(
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ >= 0;
}
friend constexpr bool operator==(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 == v.value_;
}
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return !v.is_ordered() || 0 != v.value_;
}
friend constexpr bool operator<(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 < v.value_;
}
friend constexpr bool operator<=(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 <= v.value_;
}
friend constexpr bool operator>(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 > v.value_;
}
friend constexpr bool operator>=(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 >= v.value_;
}
friend constexpr bool operator==(partial_ordering v1,
partial_ordering v2) noexcept {
return v1.value_ == v2.value_;
}
friend constexpr bool operator!=(partial_ordering v1,
partial_ordering v2) noexcept {
return v1.value_ != v2.value_;
}
private:
compare_internal::value_type value_;
};
ABSL_COMPARE_INLINE_INIT(partial_ordering, less, compare_internal::ord::less);
ABSL_COMPARE_INLINE_INIT(partial_ordering, equivalent,
compare_internal::eq::equivalent);
ABSL_COMPARE_INLINE_INIT(partial_ordering, greater,
compare_internal::ord::greater);
ABSL_COMPARE_INLINE_INIT(partial_ordering, unordered,
compare_internal::ncmp::unordered);
class weak_ordering
: public compare_internal::weak_ordering_base<weak_ordering> {
explicit constexpr weak_ordering(compare_internal::eq v) noexcept
: value_(static_cast<compare_internal::value_type>(v)) {}
explicit constexpr weak_ordering(compare_internal::ord v) noexcept
: value_(static_cast<compare_internal::value_type>(v)) {}
friend struct compare_internal::weak_ordering_base<weak_ordering>;
public:
ABSL_COMPARE_INLINE_SUBCLASS_DECL(weak_ordering, less);
ABSL_COMPARE_INLINE_SUBCLASS_DECL(weak_ordering, equivalent);
ABSL_COMPARE_INLINE_SUBCLASS_DECL(weak_ordering, greater);
// Conversions
constexpr operator partial_ordering() const noexcept { // NOLINT
return value_ == 0 ? partial_ordering::equivalent
: (value_ < 0 ? partial_ordering::less
: partial_ordering::greater);
}
// Comparisons
friend constexpr bool operator==(
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ == 0;
}
friend constexpr bool operator!=(
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ != 0;
}
friend constexpr bool operator<(
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ < 0;
}
friend constexpr bool operator<=(
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ <= 0;
}
friend constexpr bool operator>(
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ > 0;
}
friend constexpr bool operator>=(
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ >= 0;
}
friend constexpr bool operator==(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 == v.value_;
}
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 != v.value_;
}
friend constexpr bool operator<(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 < v.value_;
}
friend constexpr bool operator<=(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 <= v.value_;
}
friend constexpr bool operator>(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 > v.value_;
}
friend constexpr bool operator>=(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 >= v.value_;
}
friend constexpr bool operator==(weak_ordering v1,
weak_ordering v2) noexcept {
return v1.value_ == v2.value_;
}
friend constexpr bool operator!=(weak_ordering v1,
weak_ordering v2) noexcept {
return v1.value_ != v2.value_;
}
private:
compare_internal::value_type value_;
};
ABSL_COMPARE_INLINE_INIT(weak_ordering, less, compare_internal::ord::less);
ABSL_COMPARE_INLINE_INIT(weak_ordering, equivalent,
compare_internal::eq::equivalent);
ABSL_COMPARE_INLINE_INIT(weak_ordering, greater,
compare_internal::ord::greater);
class strong_ordering
: public compare_internal::strong_ordering_base<strong_ordering> {
explicit constexpr strong_ordering(compare_internal::eq v) noexcept
: value_(static_cast<compare_internal::value_type>(v)) {}
explicit constexpr strong_ordering(compare_internal::ord v) noexcept
: value_(static_cast<compare_internal::value_type>(v)) {}
friend struct compare_internal::strong_ordering_base<strong_ordering>;
public:
ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_ordering, less);
ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_ordering, equal);
ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_ordering, equivalent);
ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_ordering, greater);
// Conversions
constexpr operator partial_ordering() const noexcept { // NOLINT
return value_ == 0 ? partial_ordering::equivalent
: (value_ < 0 ? partial_ordering::less
: partial_ordering::greater);
}
constexpr operator weak_ordering() const noexcept { // NOLINT
return value_ == 0
? weak_ordering::equivalent
: (value_ < 0 ? weak_ordering::less : weak_ordering::greater);
}
// Comparisons
friend constexpr bool operator==(
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ == 0;
}
friend constexpr bool operator!=(
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ != 0;
}
friend constexpr bool operator<(
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ < 0;
}
friend constexpr bool operator<=(
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ <= 0;
}
friend constexpr bool operator>(
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ > 0;
}
friend constexpr bool operator>=(
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ >= 0;
}
friend constexpr bool operator==(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 == v.value_;
}
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 != v.value_;
}
friend constexpr bool operator<(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 < v.value_;
}
friend constexpr bool operator<=(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 <= v.value_;
}
friend constexpr bool operator>(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 > v.value_;
}
friend constexpr bool operator>=(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 >= v.value_;
}
friend constexpr bool operator==(strong_ordering v1,
strong_ordering v2) noexcept {
return v1.value_ == v2.value_;
}
friend constexpr bool operator!=(strong_ordering v1,
strong_ordering v2) noexcept {
return v1.value_ != v2.value_;
}
private:
compare_internal::value_type value_;
};
ABSL_COMPARE_INLINE_INIT(strong_ordering, less, compare_internal::ord::less);
ABSL_COMPARE_INLINE_INIT(strong_ordering, equal, compare_internal::eq::equal);
ABSL_COMPARE_INLINE_INIT(strong_ordering, equivalent,
compare_internal::eq::equivalent);
ABSL_COMPARE_INLINE_INIT(strong_ordering, greater,
compare_internal::ord::greater);
#undef ABSL_COMPARE_INLINE_BASECLASS_DECL
#undef ABSL_COMPARE_INLINE_SUBCLASS_DECL
#undef ABSL_COMPARE_INLINE_INIT
#endif // ABSL_USES_STD_ORDERING
namespace compare_internal {
// We also provide these comparator adapter functions for internal absl use.
// Helper functions to do a boolean comparison of two keys given a boolean
// or three-way comparator.
// SFINAE prevents implicit conversions to bool (such as from int).
template <typename BoolT,
absl::enable_if_t<std::is_same<bool, BoolT>::value, int> = 0>
constexpr bool compare_result_as_less_than(const BoolT r) { return r; }
constexpr bool compare_result_as_less_than(const absl::weak_ordering r) {
return r < 0;
}
template <typename Compare, typename K, typename LK>
constexpr bool do_less_than_comparison(const Compare &compare, const K &x,
const LK &y) {
return compare_result_as_less_than(compare(x, y));
}
// Helper functions to do a three-way comparison of two keys given a boolean or
// three-way comparator.
// SFINAE prevents implicit conversions to int (such as from bool).
template <typename Int,
absl::enable_if_t<std::is_same<int, Int>::value, int> = 0>
constexpr absl::weak_ordering compare_result_as_ordering(const Int c) {
return c < 0 ? absl::weak_ordering::less
: c == 0 ? absl::weak_ordering::equivalent
: absl::weak_ordering::greater;
}
constexpr absl::weak_ordering compare_result_as_ordering(
const absl::weak_ordering c) {
return c;
}
template <
typename Compare, typename K, typename LK,
absl::enable_if_t<!std::is_same<bool, absl::result_of_t<Compare(
const K &, const LK &)>>::value,
int> = 0>
constexpr absl::weak_ordering do_three_way_comparison(const Compare &compare,
const K &x, const LK &y) {
return compare_result_as_ordering(compare(x, y));
}
template <
typename Compare, typename K, typename LK,
absl::enable_if_t<std::is_same<bool, absl::result_of_t<Compare(
const K &, const LK &)>>::value,
int> = 0>
constexpr absl::weak_ordering do_three_way_comparison(const Compare &compare,
const K &x, const LK &y) {
return compare(x, y) ? absl::weak_ordering::less
: compare(y, x) ? absl::weak_ordering::greater
: absl::weak_ordering::equivalent;
}
} // namespace compare_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_TYPES_COMPARE_H_