--- /dev/null
+// 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::weak_equality`, `absl::strong_equality`,
+// `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::weak_equality`, 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 <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <type_traits>
+
+#include "absl/base/attributes.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+namespace compare_internal {
+
+using value_type = int8_t;
+
+template <typename T>
+struct Fail {
+ static_assert(sizeof(T) < 0, "Only literal `0` is allowed.");
+};
+
+// We need the NullPtrT template to avoid triggering the modernize-use-nullptr
+// ClangTidy warning in user code.
+template <typename NullPtrT = std::nullptr_t>
+struct OnlyLiteralZero {
+ constexpr OnlyLiteralZero(NullPtrT) noexcept {} // NOLINT
+
+ // 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,
+ typename = typename Fail<T>::type>
+ OnlyLiteralZero(T); // NOLINT
+};
+
+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 };
+
+// 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 weak_equality_base {
+ ABSL_CONST_INIT static const T equivalent;
+ ABSL_CONST_INIT static const T nonequivalent;
+};
+template <typename T>
+const T weak_equality_base<T>::equivalent(eq::equivalent);
+template <typename T>
+const T weak_equality_base<T>::nonequivalent(eq::nonequivalent);
+
+template <typename T>
+struct strong_equality_base {
+ ABSL_CONST_INIT static const T equal;
+ ABSL_CONST_INIT static const T nonequal;
+ ABSL_CONST_INIT static const T equivalent;
+ ABSL_CONST_INIT static const T nonequivalent;
+};
+template <typename T>
+const T strong_equality_base<T>::equal(eq::equal);
+template <typename T>
+const T strong_equality_base<T>::nonequal(eq::nonequal);
+template <typename T>
+const T strong_equality_base<T>::equivalent(eq::equivalent);
+template <typename T>
+const T strong_equality_base<T>::nonequivalent(eq::nonequivalent);
+
+template <typename T>
+struct partial_ordering_base {
+ ABSL_CONST_INIT static const T less;
+ ABSL_CONST_INIT static const T equivalent;
+ ABSL_CONST_INIT static const T greater;
+ ABSL_CONST_INIT static const T unordered;
+};
+template <typename T>
+const T partial_ordering_base<T>::less(ord::less);
+template <typename T>
+const T partial_ordering_base<T>::equivalent(eq::equivalent);
+template <typename T>
+const T partial_ordering_base<T>::greater(ord::greater);
+template <typename T>
+const T partial_ordering_base<T>::unordered(ncmp::unordered);
+
+template <typename T>
+struct weak_ordering_base {
+ ABSL_CONST_INIT static const T less;
+ ABSL_CONST_INIT static const T equivalent;
+ ABSL_CONST_INIT static const T greater;
+};
+template <typename T>
+const T weak_ordering_base<T>::less(ord::less);
+template <typename T>
+const T weak_ordering_base<T>::equivalent(eq::equivalent);
+template <typename T>
+const T weak_ordering_base<T>::greater(ord::greater);
+
+template <typename T>
+struct strong_ordering_base {
+ ABSL_CONST_INIT static const T less;
+ ABSL_CONST_INIT static const T equal;
+ ABSL_CONST_INIT static const T equivalent;
+ ABSL_CONST_INIT static const T greater;
+};
+template <typename T>
+const T strong_ordering_base<T>::less(ord::less);
+template <typename T>
+const T strong_ordering_base<T>::equal(eq::equal);
+template <typename T>
+const T strong_ordering_base<T>::equivalent(eq::equivalent);
+template <typename T>
+const T strong_ordering_base<T>::greater(ord::greater);
+
+} // namespace compare_internal
+
+class weak_equality
+ : public compare_internal::weak_equality_base<weak_equality> {
+ explicit constexpr weak_equality(compare_internal::eq v) noexcept
+ : value_(static_cast<compare_internal::value_type>(v)) {}
+ friend struct compare_internal::weak_equality_base<weak_equality>;
+
+ public:
+ // Comparisons
+ friend constexpr bool operator==(
+ weak_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
+ return v.value_ == 0;
+ }
+ friend constexpr bool operator!=(
+ weak_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
+ return v.value_ != 0;
+ }
+ friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
+ weak_equality v) noexcept {
+ return 0 == v.value_;
+ }
+ friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
+ weak_equality v) noexcept {
+ return 0 != v.value_;
+ }
+
+ private:
+ compare_internal::value_type value_;
+};
+
+class strong_equality
+ : public compare_internal::strong_equality_base<strong_equality> {
+ explicit constexpr strong_equality(compare_internal::eq v) noexcept
+ : value_(static_cast<compare_internal::value_type>(v)) {}
+ friend struct compare_internal::strong_equality_base<strong_equality>;
+
+ public:
+ // Conversion
+ constexpr operator weak_equality() const noexcept { // NOLINT
+ return value_ == 0 ? weak_equality::equivalent
+ : weak_equality::nonequivalent;
+ }
+ // Comparisons
+ friend constexpr bool operator==(
+ strong_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
+ return v.value_ == 0;
+ }
+ friend constexpr bool operator!=(
+ strong_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
+ return v.value_ != 0;
+ }
+ friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
+ strong_equality v) noexcept {
+ return 0 == v.value_;
+ }
+ friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
+ strong_equality v) noexcept {
+ return 0 != v.value_;
+ }
+
+ private:
+ compare_internal::value_type value_;
+};
+
+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:
+ // Conversion
+ constexpr operator weak_equality() const noexcept { // NOLINT
+ return value_ == 0 ? weak_equality::equivalent
+ : weak_equality::nonequivalent;
+ }
+ // 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_;
+ }
+
+ private:
+ compare_internal::value_type value_;
+};
+
+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:
+ // Conversions
+ constexpr operator weak_equality() const noexcept { // NOLINT
+ return value_ == 0 ? weak_equality::equivalent
+ : weak_equality::nonequivalent;
+ }
+ 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_;
+ }
+
+ private:
+ compare_internal::value_type value_;
+};
+
+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:
+ // Conversions
+ constexpr operator weak_equality() const noexcept { // NOLINT
+ return value_ == 0 ? weak_equality::equivalent
+ : weak_equality::nonequivalent;
+ }
+ constexpr operator strong_equality() const noexcept { // NOLINT
+ return value_ == 0 ? strong_equality::equal : strong_equality::nonequal;
+ }
+ 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_;
+ }
+
+ private:
+ compare_internal::value_type value_;
+};
+
+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 Bool,
+ absl::enable_if_t<std::is_same<bool, Bool>::value, int> = 0>
+constexpr bool compare_result_as_less_than(const Bool 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
+} // namespace absl
+
+#endif // ABSL_TYPES_COMPARE_H_
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