Merge pull request #115 from tcbrindle/pr/cmp_min_max

Add cmp::min cmp::max
tcbrindle · Aug 8, 2023 · 8048d83 · 8048d83
2 parents 6949f23 + 44a3078
commit 8048d83
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diff --git a/include/flux/core/functional.hpp b/include/flux/core/functional.hpp
@@ -253,6 +253,39 @@ FLUX_EXPORT inline constexpr auto odd = detail::predicate([](auto const& val) ->
 
 } // namespace pred
 
+namespace cmp {
+
+namespace detail {
+
+struct min_fn {
+    template <typename T, typename U, typename Cmp = std::ranges::less>
+        requires std::strict_weak_order<Cmp&, T&, U&>
+    [[nodiscard]]
+    constexpr auto operator()(T&& t, U&& u, Cmp cmp = Cmp{}) const
+        -> std::common_reference_t<T, U>
+    {
+        return std::invoke(cmp, u, t) ? FLUX_FWD(u) : FLUX_FWD(t);
+    }
+};
+
+struct max_fn {
+    template <typename T, typename U, typename Cmp = std::ranges::less>
+        requires std::strict_weak_order<Cmp&, T&, U&>
+    [[nodiscard]]
+    constexpr auto operator()(T&& t, U&& u, Cmp cmp = Cmp{}) const
+        -> std::common_reference_t<T, U>
+    {
+        return !std::invoke(cmp, u, t) ? FLUX_FWD(u) : FLUX_FWD(t);
+    }
+};
+
+} // namespace detail
+
+FLUX_EXPORT inline constexpr auto min = detail::min_fn{};
+FLUX_EXPORT inline constexpr auto max = detail::max_fn{};
+
+} // namespace cmp
+
 } // namespace flux
 
 #endif
diff --git a/test/test_predicates.cpp b/test/test_predicates.cpp
@@ -118,6 +118,134 @@ constexpr bool test_predicate_combiners()
 }
 static_assert(test_predicate_combiners());
 
+// Not really predicates, but we'll test them here anyway
+constexpr bool test_comparisons()
+{
+    namespace cmp = flux::cmp;
+
+    struct Test {
+        int i;
+        double d;
+
+        bool operator==(Test const&) const = default;
+    };
+
+    // min of two same-type non-const lvalue references is an lvalue
+    {
+        int i = 0, j = 1;
+        cmp::min(i, j) = 99;
+        STATIC_CHECK(i == 99);
+        STATIC_CHECK(j == 1);
+    }
+
+    // min of same-type mixed-const lvalue refs is a const ref
+    {
+        int i = 1;
+        int const j = 0;
+        auto& m = cmp::min(i, j);
+        static_assert(std::same_as<decltype(m), int const&>);
+        STATIC_CHECK(m == 0);
+    }
+
+    // min of same-type lvalue and prvalue is a prvalue
+    {
+        int const i = 1;
+        using M = decltype(cmp::min(i, i + 1));
+        static_assert(std::same_as<M, int>);
+        STATIC_CHECK(cmp::min(i, i + 1) == 1);
+    }
+
+    // mixed-type min is a prvalue
+    {
+        int const i = 10;
+        long const j = 5;
+        using M = decltype(cmp::min(i, j));
+        static_assert(std::same_as<M, long>);
+        STATIC_CHECK(cmp::min(i, j) == 5);
+    }
+
+    // Custom comparators work okay with min()
+    {
+        Test t1{1, 3.0};
+        Test t2{1, 2.0};
+
+        auto cmp_test = [](Test t1, Test t2) { return t1.d < t2.d; };
+
+        STATIC_CHECK(cmp::min(t1, t2, cmp_test) == t2);
+    }
+
+    // If arguments are equal, min() returns the first
+    {
+        int i = 1, j = 1;
+        int& m = cmp::min(i, j);
+        STATIC_CHECK(&m == &i);
+
+        Test t1{1, 3.0};
+        Test t2{1, 2.0};
+
+        STATIC_CHECK(cmp::min(t1, t2, flux::proj(std::less{}, &Test::i)) == t1);
+    }
+
+    // max of two same-type non-const lvalue references is an lvalue
+    {
+        int i = 0, j = 1;
+        cmp::max(i, j) = 99;
+        STATIC_CHECK(i == 0);
+        STATIC_CHECK(j == 99);
+    }
+
+    // max of same-type mixed-const lvalue refs is a const ref
+    {
+        int i = 1;
+        int const j = 0;
+        auto& m = cmp::max(i, j);
+        static_assert(std::same_as<decltype(m), int const&>);
+        STATIC_CHECK(m == 1);
+    }
+
+    // max of same-type lvalue and prvalue is a prvalue
+    {
+        int const i = 1;
+        using M = decltype(cmp::max(i, i + 1));
+        static_assert(std::same_as<M, int>);
+        STATIC_CHECK(cmp::max(i, i + 1) == 2);
+    }
+
+    // mixed-type max is a prvalue
+    {
+        int const i = 10;
+        long const j = 5;
+        using M = decltype(cmp::max(i, j));
+        static_assert(std::same_as<M, long>);
+        STATIC_CHECK(cmp::max(i, j) == 10);
+    }
+
+    // Custom comparators work okay with max()
+    {
+        Test t1{1, 3.0};
+        Test t2{1, 2.0};
+
+        auto cmp_test = [](Test t1, Test t2) { return t1.d < t2.d; };
+
+        STATIC_CHECK(cmp::max(t1, t2, cmp_test) == t1);
+    }
+
+    // If arguments are equal, max() returns the second
+    {
+        int i = 1, j = 1;
+        int& m = cmp::max(i, j);
+        STATIC_CHECK(&m == &j);
+
+        Test t1{1, 3.0};
+        Test t2{1, 2.0};
+
+        STATIC_CHECK(cmp::max(t1, t2, flux::proj(std::less{}, &Test::i)) == t2);
+    }
+
+    return true;
+}
+static_assert(test_comparisons());
+
 }
 
 TEST_CASE("predicates")
@@ -126,3 +254,8 @@ TEST_CASE("predicates")
     REQUIRE(test_predicate_combiners());
 }
 
+TEST_CASE("comparators")
+{
+    REQUIRE(test_comparisons());
+}
+