Add traits for checking whether types are comparable

1 files changed, 74 insertions, 0 deletions

diff --git a/tests/SelfTest/IntrospectiveTests/Traits.tests.cpp b/tests/SelfTest/IntrospectiveTests/Traits.tests.cpp
new file mode 100644
index 00000000..35d30c76
--- /dev/null
+++ b/tests/SelfTest/IntrospectiveTests/Traits.tests.cpp
@@ -0,0 +1,74 @@
+
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/internal/catch_compare_traits.hpp>
+
+// Should only be constructible from literal 0.
+// Used by `TypeWithLit0Comparisons` for testing comparison
+// ops that only work with literal zero, the way std::*orderings do
+struct ZeroLiteralDetector {
+    constexpr ZeroLiteralDetector( ZeroLiteralDetector* ) noexcept {}
+
+    template <typename T,
+              typename = std::enable_if_t<!std::is_same<T, int>::value>>
+    constexpr ZeroLiteralDetector( T ) = delete;
+};
+
+struct TypeWithLit0Comparisons {
+#define DEFINE_COMP_OP( op )                                                  \
+    friend bool operator op( TypeWithLit0Comparisons, ZeroLiteralDetector ) { \
+        return true;                                                          \
+    }                                                                         \
+    friend bool operator op( ZeroLiteralDetector, TypeWithLit0Comparisons ) { \
+        return false;                                                          \
+    }
+
+    DEFINE_COMP_OP( < )
+    DEFINE_COMP_OP( <= )
+    DEFINE_COMP_OP( > )
+    DEFINE_COMP_OP( >= )
+    DEFINE_COMP_OP( == )
+    DEFINE_COMP_OP( != )
+
+#undef DEFINE_COMP_OP
+};
+
+
+#define ADD_TRAIT_TEST_CASE( op )                                         \
+    TEST_CASE( "is_" #op "_comparable",                                   \
+               "[traits][is_comparable][approvals]" ) {                   \
+        using Catch::Detail::is_##op##_0_comparable;                      \
+        using Catch::Detail::is_##op##_comparable;                        \
+                                                                          \
+        STATIC_REQUIRE( is_##op##_comparable<int, int>::value );          \
+        STATIC_REQUIRE(                                                   \
+            is_##op##_comparable<std::string, std::string>::value );      \
+        STATIC_REQUIRE( !is_##op##_comparable<int, std::string>::value ); \
+        STATIC_REQUIRE(                                                   \
+            !is_##op##_comparable<TypeWithLit0Comparisons, int>::value ); \
+        STATIC_REQUIRE(                                                   \
+            !is_##op##_comparable<int, TypeWithLit0Comparisons>::value ); \
+                                                                          \
+        STATIC_REQUIRE( is_##op##_0_comparable<int>::value );             \
+        STATIC_REQUIRE(                                                   \
+            is_##op##_0_comparable<TypeWithLit0Comparisons>::value );     \
+        STATIC_REQUIRE( !is_##op##_0_comparable<std::string>::value );    \
+                                                                          \
+    /* This test fails with MSVC in permissive mode, because of course it does */ \
+    /* STATIC_REQUIRE( !is_##op##_0_comparable<int*>::value ); */ \
+}
+
+ADD_TRAIT_TEST_CASE(lt)
+ADD_TRAIT_TEST_CASE(gt)
+ADD_TRAIT_TEST_CASE(le)
+ADD_TRAIT_TEST_CASE(ge)
+ADD_TRAIT_TEST_CASE(eq)
+ADD_TRAIT_TEST_CASE(ne)
+
+#undef ADD_TRAIT_TEST_CASE