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Implement P2167R3 Improving boolean-testable Usage (for comparison fallback CPOs) #3258

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merged 3 commits into from
Dec 6, 2022
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Implement P2167R3 Improving boolean-testable Usage (for comparison fallback CPOs) #3258

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6812458
Test coverage for CPO changes in P2162R3
frederick-vs-ja Dec 2, 2022
d79975e
Implement changes for CPOs in P2167R3
frederick-vs-ja Dec 2, 2022
123e763
Fix typo: s/P2162R3/P2167R3
frederick-vs-ja Dec 3, 2022
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10 changes: 5 additions & 5 deletions stl/inc/compare
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Original file line number Diff line number Diff line change
Expand Up @@ -641,8 +641,8 @@ inline namespace _Cpos {

template <class _Ty1, class _Ty2>
concept _Can_fallback_eq_lt = requires(_Ty1& _Left, _Ty2& _Right) {
{ _Left == _Right } -> _Implicitly_convertible_to<bool>;
{ _Left < _Right } -> _Implicitly_convertible_to<bool>;
{ _Left == _Right } -> _Boolean_testable;
{ _Left < _Right } -> _Boolean_testable;
};

template <class _Ty1, class _Ty2>
Expand Down Expand Up @@ -751,9 +751,9 @@ concept _Can_partial_order = requires(_Ty1& _Left, _Ty2& _Right) { _STD partial_
namespace _Compare_partial_order_fallback {
template <class _Ty1, class _Ty2>
concept _Can_fallback_eq_lt_twice = requires(_Ty1& _Left, _Ty2& _Right) {
{ _Left == _Right } -> _Implicitly_convertible_to<bool>;
{ _Left < _Right } -> _Implicitly_convertible_to<bool>;
{ _Right < _Left } -> _Implicitly_convertible_to<bool>;
{ _Left == _Right } -> _Boolean_testable;
{ _Left < _Right } -> _Boolean_testable;
{ _Right < _Left } -> _Boolean_testable;
};

class _Cpo {
Expand Down
1 change: 1 addition & 0 deletions stl/inc/yvals_core.h
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Expand Up @@ -265,6 +265,7 @@
// P2102R0 Making "Implicit Expression Variations" More Explicit
// P2106R0 Range Algorithm Result Types
// P2116R0 Removing tuple-Like Protocol Support From Fixed-Extent span
// P2167R3 Improving boolean-testable Usage
// P2210R2 Superior String Splitting
// P2216R3 std::format Improvements
// P2231R1 Completing constexpr In optional And variant
Expand Down
59 changes: 59 additions & 0 deletions tests/std/tests/P0768R1_spaceship_cpos/test.cpp
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Expand Up @@ -326,6 +326,65 @@ namespace {
static_assert(is_same_v<CpoResult<compare_partial_order_fallback, F<13>, const F<13>>, Partial>); // [cmp.alg]/6.3
} // namespace

// Test strengthened requirements in P2167R3: compare_*_order_fallback CPOs require return types to be boolean-testable.
enum class ResultKind : bool {
Bad,
Good,
};

template <ResultKind K>
struct ComparisonResult {
bool value;

constexpr operator bool() const noexcept {
return value;
}

constexpr auto operator!() const noexcept {
if constexpr (K == ResultKind::Good) {
return ComparisonResult{!value};
}
}
};

template <ResultKind EqKind, ResultKind LeKind>
struct BoolTestType {
friend constexpr ComparisonResult<EqKind> operator==(BoolTestType, BoolTestType) noexcept {
return ComparisonResult<EqKind>{true};
}

friend constexpr ComparisonResult<LeKind> operator<(BoolTestType, BoolTestType) noexcept {
return ComparisonResult<LeKind>{false};
}
};

static_assert(is_same_v<CpoResult<compare_strong_order_fallback, BoolTestType<ResultKind::Bad, ResultKind::Bad>>,
IllFormed>); // [cmp.alg]/4.3
static_assert(is_same_v<CpoResult<compare_strong_order_fallback, BoolTestType<ResultKind::Bad, ResultKind::Good>>,
IllFormed>); // [cmp.alg]/4.3
static_assert(is_same_v<CpoResult<compare_strong_order_fallback, BoolTestType<ResultKind::Good, ResultKind::Bad>>,
IllFormed>); // [cmp.alg]/4.3
static_assert(is_same_v<CpoResult<compare_strong_order_fallback, BoolTestType<ResultKind::Good, ResultKind::Good>>,
strong_ordering>); // [cmp.alg]/4.3

static_assert(is_same_v<CpoResult<compare_weak_order_fallback, BoolTestType<ResultKind::Bad, ResultKind::Bad>>,
IllFormed>); // [cmp.alg]/5.3
static_assert(is_same_v<CpoResult<compare_weak_order_fallback, BoolTestType<ResultKind::Bad, ResultKind::Good>>,
IllFormed>); // [cmp.alg]/5.3
static_assert(is_same_v<CpoResult<compare_weak_order_fallback, BoolTestType<ResultKind::Good, ResultKind::Bad>>,
IllFormed>); // [cmp.alg]/5.3
static_assert(is_same_v<CpoResult<compare_weak_order_fallback, BoolTestType<ResultKind::Good, ResultKind::Good>>,
weak_ordering>); // [cmp.alg]/5.3

static_assert(is_same_v<CpoResult<compare_partial_order_fallback, BoolTestType<ResultKind::Bad, ResultKind::Bad>>,
IllFormed>); // [cmp.alg]/6.3
static_assert(is_same_v<CpoResult<compare_partial_order_fallback, BoolTestType<ResultKind::Bad, ResultKind::Good>>,
IllFormed>); // [cmp.alg]/6.3
static_assert(is_same_v<CpoResult<compare_partial_order_fallback, BoolTestType<ResultKind::Good, ResultKind::Bad>>,
IllFormed>); // [cmp.alg]/6.3
static_assert(is_same_v<CpoResult<compare_partial_order_fallback, BoolTestType<ResultKind::Good, ResultKind::Good>>,
partial_ordering>); // [cmp.alg]/6.3

// Test when the type is comparable through ADL. Part B, exception specifications.
static_assert(!NoexceptCpo<std::strong_order, TestAdl::StrongType<Throwing>>); // [cmp.alg]/1.2
static_assert(!NoexceptCpo<std::weak_order, TestAdl::WeakType<Throwing>>); // [cmp.alg]/2.2
Expand Down