diff options
Diffstat (limited to 'absl/meta')
| -rw-r--r-- | absl/meta/type_traits.h | 44 | ||||
| -rw-r--r-- | absl/meta/type_traits_test.cc | 81 |
2 files changed, 123 insertions, 2 deletions
diff --git a/absl/meta/type_traits.h b/absl/meta/type_traits.h index 8d3264f100db..457b890841a6 100644 --- a/absl/meta/type_traits.h +++ b/absl/meta/type_traits.h @@ -44,6 +44,7 @@ namespace absl { namespace type_traits_internal { + template <typename... Ts> struct VoidTImpl { using type = void; @@ -61,6 +62,49 @@ struct default_alignment_of_aligned_storage<Len, static constexpr size_t value = Align; }; +//////////////////////////////// +// Library Fundamentals V2 TS // +//////////////////////////////// + +// NOTE: The `is_detected` family of templates here differ from the library +// fundamentals specification in that for library fundamentals, `Op<Args...>` is +// evaluated as soon as the type `is_detected<Op, Args...>` undergoes +// substitution, regardless of whether or not the `::value` is accessed. That +// is inconsistent with all other standard traits and prevents lazy evaluation +// in larger contexts (such as if the `is_detected` check is a trailing argument +// of a `conjunction`. This implementation opts to instead be lazy in the same +// way that the standard traits are (this "defect" of the detection idiom +// specifications has been reported). + +template <class Enabler, template <class...> class Op, class... Args> +struct is_detected_impl { + using type = std::false_type; +}; + +template <template <class...> class Op, class... Args> +struct is_detected_impl<typename VoidTImpl<Op<Args...>>::type, Op, Args...> { + using type = std::true_type; +}; + +template <template <class...> class Op, class... Args> +struct is_detected : is_detected_impl<void, Op, Args...>::type {}; + +template <class Enabler, class To, template <class...> class Op, class... Args> +struct is_detected_convertible_impl { + using type = std::false_type; +}; + +template <class To, template <class...> class Op, class... Args> +struct is_detected_convertible_impl< + typename std::enable_if<std::is_convertible<Op<Args...>, To>::value>::type, + To, Op, Args...> { + using type = std::true_type; +}; + +template <class To, template <class...> class Op, class... Args> +struct is_detected_convertible + : is_detected_convertible_impl<void, To, Op, Args...>::type {}; + } // namespace type_traits_internal // void_t() diff --git a/absl/meta/type_traits_test.cc b/absl/meta/type_traits_test.cc index 9dd95429a5a1..81b4bd323977 100644 --- a/absl/meta/type_traits_test.cc +++ b/absl/meta/type_traits_test.cc @@ -34,6 +34,83 @@ struct simple_pair { struct Dummy {}; +struct ReturnType {}; +struct ConvertibleToReturnType { + operator ReturnType() const; // NOLINT +}; + +// Unique types used as parameter types for testing the detection idiom. +struct StructA {}; +struct StructB {}; +struct StructC {}; + +struct TypeWithBarFunction { + template <class T, + absl::enable_if_t<std::is_same<T&&, StructA&>::value, int> = 0> + ReturnType bar(T&&, const StructB&, StructC&&) &&; // NOLINT +}; + +struct TypeWithBarFunctionAndConvertibleReturnType { + template <class T, + absl::enable_if_t<std::is_same<T&&, StructA&>::value, int> = 0> + ConvertibleToReturnType bar(T&&, const StructB&, StructC&&) &&; // NOLINT +}; + +template <class Class, class... Ts> +using BarIsCallableImpl = + decltype(std::declval<Class>().bar(std::declval<Ts>()...)); + +template <class Class, class... T> +using BarIsCallable = + absl::type_traits_internal::is_detected<BarIsCallableImpl, Class, T...>; + +template <class Class, class... T> +using BarIsCallableConv = absl::type_traits_internal::is_detected_convertible< + ReturnType, BarIsCallableImpl, Class, T...>; + +// NOTE: Test of detail type_traits_internal::is_detected. +TEST(IsDetectedTest, BasicUsage) { + EXPECT_TRUE((BarIsCallable<TypeWithBarFunction, StructA&, const StructB&, + StructC>::value)); + EXPECT_TRUE( + (BarIsCallable<TypeWithBarFunction, StructA&, StructB&, StructC>::value)); + EXPECT_TRUE( + (BarIsCallable<TypeWithBarFunction, StructA&, StructB, StructC>::value)); + + EXPECT_FALSE((BarIsCallable<int, StructA&, const StructB&, StructC>::value)); + EXPECT_FALSE((BarIsCallable<TypeWithBarFunction&, StructA&, const StructB&, + StructC>::value)); + EXPECT_FALSE((BarIsCallable<TypeWithBarFunction, StructA, const StructB&, + StructC>::value)); +} + +// NOTE: Test of detail type_traits_internal::is_detected_convertible. +TEST(IsDetectedConvertibleTest, BasicUsage) { + EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunction, StructA&, const StructB&, + StructC>::value)); + EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunction, StructA&, StructB&, + StructC>::value)); + EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunction, StructA&, StructB, + StructC>::value)); + EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType, + StructA&, const StructB&, StructC>::value)); + EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType, + StructA&, StructB&, StructC>::value)); + EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType, + StructA&, StructB, StructC>::value)); + + EXPECT_FALSE( + (BarIsCallableConv<int, StructA&, const StructB&, StructC>::value)); + EXPECT_FALSE((BarIsCallableConv<TypeWithBarFunction&, StructA&, + const StructB&, StructC>::value)); + EXPECT_FALSE((BarIsCallableConv<TypeWithBarFunction, StructA, const StructB&, + StructC>::value)); + EXPECT_FALSE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType&, + StructA&, const StructB&, StructC>::value)); + EXPECT_FALSE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType, + StructA, const StructB&, StructC>::value)); +} + TEST(VoidTTest, BasicUsage) { StaticAssertTypeEq<void, absl::void_t<Dummy>>(); StaticAssertTypeEq<void, absl::void_t<Dummy, Dummy, Dummy>>(); @@ -718,8 +795,8 @@ TEST(TypeTraitsTest, TestDecay) { ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int[][1]); ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int()); - ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int(float)); - ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int(char, ...)); + ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int(float)); // NOLINT + ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int(char, ...)); // NOLINT } struct TypeA {}; |