//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++03, c++11, c++14, c++17
// constexpr auto synth-three-way = ...;
// via std::tuple<T>(t) <=> std::tuple<U>(u), which exposes its behavior most directly
#include "test_macros.h"
TEST_CLANG_DIAGNOSTIC_IGNORED("-Wsign-compare")
TEST_GCC_DIAGNOSTIC_IGNORED("-Wsign-compare")
TEST_MSVC_DIAGNOSTIC_IGNORED(4242 4244) // Various truncation warnings
#include <cassert>
#include <compare>
#include <limits> // quiet_NaN
#include <tuple>
#include <type_traits>
#include <utility> // declval
template <typename T, typename U = T>
concept can_synth_three_way = requires(T t, U u) { std::tuple<T>(t) <=> std::tuple<U>(u); };
template <typename T, typename U>
constexpr auto synth_three_way(const T& t, const U& u) {
return std::tuple<T>(t) <=> std::tuple<U>(u);
}
template <typename T, typename U>
using synth_three_way_result = decltype(std::declval<std::tuple<T>>() <=> std::declval<std::tuple<U>>());
// A custom three-way result type
struct CustomEquality {
friend constexpr bool operator==(const CustomEquality&, int) noexcept { return true; }
friend constexpr bool operator<(const CustomEquality&, int) noexcept { return false; }
friend constexpr bool operator<(int, const CustomEquality&) noexcept { return false; }
};
constexpr bool test() {
{
assert(synth_three_way(1, 1) == std::strong_ordering::equal);
assert(synth_three_way(2, 1) == std::strong_ordering::greater);
assert(synth_three_way(1, 2) == std::strong_ordering::less);
ASSERT_SAME_TYPE(std::strong_ordering, synth_three_way_result<int, int>);
ASSERT_SAME_TYPE(std::strong_ordering, synth_three_way_result<short, long long int>);
}
{
constexpr double nan = std::numeric_limits<double>::quiet_NaN();
assert(synth_three_way(1.0, 1.0) == std::partial_ordering::equivalent);
assert(synth_three_way(2.0, 1.0) == std::partial_ordering::greater);
assert(synth_three_way(1.0, 2.0) == std::partial_ordering::less);
assert(synth_three_way(nan, nan) == std::partial_ordering::unordered);
ASSERT_SAME_TYPE(std::partial_ordering, synth_three_way_result<double, double>);
ASSERT_SAME_TYPE(std::partial_ordering, synth_three_way_result<double, float>);
ASSERT_SAME_TYPE(std::partial_ordering, synth_three_way_result<double, int>);
ASSERT_SAME_TYPE(std::partial_ordering, synth_three_way_result<float, short>);
}
{
struct StrongSpaceship {
int value;
constexpr bool operator==(const StrongSpaceship&) const = default;
constexpr std::strong_ordering operator<=>(const StrongSpaceship& other) const { return value <=> other.value; }
};
assert(synth_three_way(StrongSpaceship{1}, StrongSpaceship{1}) == std::strong_ordering::equal);
assert(synth_three_way(StrongSpaceship{2}, StrongSpaceship{1}) == std::strong_ordering::greater);
assert(synth_three_way(StrongSpaceship{1}, StrongSpaceship{2}) == std::strong_ordering::less);
ASSERT_SAME_TYPE(std::strong_ordering, synth_three_way_result<StrongSpaceship, StrongSpaceship>);
}
{
struct WeakSpaceship {
int value;
constexpr bool operator==(const WeakSpaceship&) const = default;
constexpr std::weak_ordering operator<=>(const WeakSpaceship& other) const {
return value <=> other.value;
}
};
assert(synth_three_way(WeakSpaceship{1}, WeakSpaceship{1}) == std::weak_ordering::equivalent);
assert(synth_three_way(WeakSpaceship{2}, WeakSpaceship{1}) == std::weak_ordering::greater);
assert(synth_three_way(WeakSpaceship{1}, WeakSpaceship{2}) == std::weak_ordering::less);
ASSERT_SAME_TYPE(std::weak_ordering, synth_three_way_result<WeakSpaceship, WeakSpaceship>);
}
{
struct PartialSpaceship {
double value;
constexpr bool operator==(const PartialSpaceship&) const = default;
constexpr std::partial_ordering operator<=>(const PartialSpaceship& other) const {
return value <=> other.value;
}
};
constexpr double nan = std::numeric_limits<double>::quiet_NaN();
assert(synth_three_way(PartialSpaceship{1.0}, PartialSpaceship{1.0}) == std::partial_ordering::equivalent);
assert(synth_three_way(PartialSpaceship{2.0}, PartialSpaceship{1.0}) == std::partial_ordering::greater);
assert(synth_three_way(PartialSpaceship{1.0}, PartialSpaceship{2.0}) == std::partial_ordering::less);
assert(synth_three_way(PartialSpaceship{nan}, PartialSpaceship{nan}) == std::partial_ordering::unordered);
ASSERT_SAME_TYPE(std::partial_ordering, synth_three_way_result<PartialSpaceship, PartialSpaceship>);
}
{
struct NoSpaceship {
int value;
constexpr bool operator==(const NoSpaceship&) const = default;
constexpr bool operator<(const NoSpaceship& other) const { return value < other.value; }
};
assert(synth_three_way(NoSpaceship{1}, NoSpaceship{1}) == std::weak_ordering::equivalent);
assert(synth_three_way(NoSpaceship{2}, NoSpaceship{1}) == std::weak_ordering::greater);
assert(synth_three_way(NoSpaceship{1}, NoSpaceship{2}) == std::weak_ordering::less);
ASSERT_SAME_TYPE(std::weak_ordering, synth_three_way_result<NoSpaceship, NoSpaceship>);
}
{
// Types with operator<=> but no operator== are not three_way_comparable and will fall back to operator< and
// compare as weakly ordered.
struct SpaceshipNoEquals {
constexpr std::strong_ordering operator<=>(const SpaceshipNoEquals&) const {
return std::strong_ordering::equivalent;
}
};
assert(synth_three_way(SpaceshipNoEquals{}, SpaceshipNoEquals{}) == std::weak_ordering::equivalent);
ASSERT_SAME_TYPE(std::weak_ordering, synth_three_way_result<SpaceshipNoEquals, SpaceshipNoEquals>);
}
{
// Custom three-way-comparison result types cannot satisfy standard concepts (and therefore synth-three-way)
// because they are not understood by std::common_comparison_category, but they can still be used in
// the same way as standard orderings to do comparisons, and thus can be used by synth-three-way to yield a
// weakly-ordered result.
struct CustomSpaceship {
constexpr CustomEquality operator<=>(const CustomSpaceship&) const { return CustomEquality(); }
};
assert((CustomSpaceship{} <=> CustomSpaceship{}) == 0);
assert(!(CustomSpaceship{} < CustomSpaceship{}));
assert(synth_three_way(CustomSpaceship{}, CustomSpaceship{}) == std::weak_ordering::equivalent);
ASSERT_SAME_TYPE(std::weak_ordering, synth_three_way_result<CustomSpaceship, CustomSpaceship>);
}
// SFINAE tests demonstrating synth-three-way needs three_way_comparable or operator<.
{
struct NoRelative {
constexpr bool operator==(const NoRelative&) const;
};
static_assert(!can_synth_three_way<NoRelative>);
}
{
struct NoLessThan {
constexpr bool operator==(const NoLessThan&) const;
constexpr bool operator>(const NoLessThan&) const;
constexpr bool operator>=(const NoLessThan&) const;
constexpr bool operator<=(const NoLessThan&) const;
};
static_assert(!can_synth_three_way<NoLessThan>);
}
{
assert(synth_three_way(1, 1U) == std::weak_ordering::equivalent);
assert(synth_three_way(-1, 0U) == std::weak_ordering::greater);
// Even with the warning suppressed (-Wno-sign-compare) there should still be no <=> operator
// between signed and unsigned types, so we should end up with a synthesized weak ordering.
ASSERT_SAME_TYPE(std::weak_ordering, synth_three_way_result<int, unsigned int>);
// When an unsigned type can be narrowed to a larger signed type, <=> should be defined and we
// should get a strong ordering. (This probably does not raise a warning due to safe narrowing.)
assert(synth_three_way(static_cast<long long int>(-1), static_cast<unsigned char>(0)) == std::strong_ordering::less);
assert(synth_three_way(static_cast<long long int>(-1), static_cast<unsigned char>(0)) == std::strong_ordering::less);
ASSERT_SAME_TYPE(std::strong_ordering, synth_three_way_result<long long int, unsigned char>);
}
#ifdef TEST_COMPILER_GCC
// GCC cannot evaluate NaN @ non-NaN constexpr, so test that runtime-only.
if (!std::is_constant_evaluated())
#endif
{
constexpr double nan = std::numeric_limits<double>::quiet_NaN();
assert(synth_three_way(nan, 1.0) == std::partial_ordering::unordered);
}
return true;
}
int main(int, char**) {
test();
static_assert(test());
return 0;
}
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