diff options
Diffstat (limited to 'absl/utility/utility.h')
| -rw-r--r-- | absl/utility/utility.h | 99 |
1 files changed, 78 insertions, 21 deletions
diff --git a/absl/utility/utility.h b/absl/utility/utility.h index 66e22dc2..bc9af048 100644 --- a/absl/utility/utility.h +++ b/absl/utility/utility.h @@ -4,7 +4,7 @@ // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // -// http://www.apache.org/licenses/LICENSE-2.0 +// https://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, @@ -25,6 +25,7 @@ // * index_sequence_for<Ts...> == std::index_sequence_for<Ts...> // * apply<Functor, Tuple> == std::apply<Functor, Tuple> // * exchange<T> == std::exchange<T> +// * make_from_tuple<T> == std::make_from_tuple<T> // // This header file also provides the tag types `in_place_t`, `in_place_type_t`, // and `in_place_index_t`, as well as the constant `in_place`, and @@ -32,10 +33,9 @@ // // References: // -// http://en.cppreference.com/w/cpp/utility/integer_sequence -// http://en.cppreference.com/w/cpp/utility/apply +// https://en.cppreference.com/w/cpp/utility/integer_sequence +// https://en.cppreference.com/w/cpp/utility/apply // http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3658.html -// #ifndef ABSL_UTILITY_UTILITY_H_ #define ABSL_UTILITY_UTILITY_H_ @@ -51,7 +51,7 @@ #include "absl/meta/type_traits.h" namespace absl { -inline namespace lts_2018_12_18 { +inline namespace lts_2019_08_08 { // integer_sequence // @@ -115,6 +115,20 @@ struct Gen<T, 0> { using type = integer_sequence<T>; }; +template <typename T> +struct InPlaceTypeTag { + explicit InPlaceTypeTag() = delete; + InPlaceTypeTag(const InPlaceTypeTag&) = delete; + InPlaceTypeTag& operator=(const InPlaceTypeTag&) = delete; +}; + +template <size_t I> +struct InPlaceIndexTag { + explicit InPlaceIndexTag() = delete; + InPlaceIndexTag(const InPlaceIndexTag&) = delete; + InPlaceIndexTag& operator=(const InPlaceIndexTag&) = delete; +}; + } // namespace utility_internal // Compile-time sequences of integers @@ -164,6 +178,7 @@ ABSL_INTERNAL_INLINE_CONSTEXPR(in_place_t, in_place, {}); #endif // ABSL_HAVE_STD_OPTIONAL #if defined(ABSL_HAVE_STD_ANY) || defined(ABSL_HAVE_STD_VARIANT) +using std::in_place_type; using std::in_place_type_t; #else @@ -173,10 +188,14 @@ using std::in_place_type_t; // be specified, such as with `absl::any`, designed to be a drop-in replacement // for C++17's `std::in_place_type_t`. template <typename T> -struct in_place_type_t {}; +using in_place_type_t = void (*)(utility_internal::InPlaceTypeTag<T>); + +template <typename T> +void in_place_type(utility_internal::InPlaceTypeTag<T>) {} #endif // ABSL_HAVE_STD_ANY || ABSL_HAVE_STD_VARIANT #ifdef ABSL_HAVE_STD_VARIANT +using std::in_place_index; using std::in_place_index_t; #else @@ -186,7 +205,10 @@ using std::in_place_index_t; // be specified, such as with `absl::any`, designed to be a drop-in replacement // for C++17's `std::in_place_index_t`. template <size_t I> -struct in_place_index_t {}; +using in_place_index_t = void (*)(utility_internal::InPlaceIndexTag<I>); + +template <size_t I> +void in_place_index(utility_internal::InPlaceIndexTag<I>) {} #endif // ABSL_HAVE_STD_VARIANT // Constexpr move and forward @@ -235,25 +257,33 @@ auto apply_helper(Functor&& functor, Tuple&& t, index_sequence<Indexes...>) // // Example: // -// class Foo{void Bar(int);}; -// void user_function(int, string); -// void user_function(std::unique_ptr<Foo>); +// class Foo { +// public: +// void Bar(int); +// }; +// void user_function1(int, std::string); +// void user_function2(std::unique_ptr<Foo>); +// auto user_lambda = [](int, int) {}; // // int main() // { -// std::tuple<int, string> tuple1(42, "bar"); -// // Invokes the user function overload on int, string. -// absl::apply(&user_function, tuple1); +// std::tuple<int, std::string> tuple1(42, "bar"); +// // Invokes the first user function on int, std::string. +// absl::apply(&user_function1, tuple1); // -// auto foo = absl::make_unique<Foo>(); -// std::tuple<Foo*, int> tuple2(foo.get(), 42); -// // Invokes the method Bar on foo with one argument 42. -// absl::apply(&Foo::Bar, foo.get(), 42); -// -// std::tuple<std::unique_ptr<Foo>> tuple3(absl::make_unique<Foo>()); +// std::tuple<std::unique_ptr<Foo>> tuple2(absl::make_unique<Foo>()); // // Invokes the user function that takes ownership of the unique // // pointer. -// absl::apply(&user_function, std::move(tuple)); +// absl::apply(&user_function2, std::move(tuple2)); +// +// auto foo = absl::make_unique<Foo>(); +// std::tuple<Foo*, int> tuple3(foo.get(), 42); +// // Invokes the method Bar on foo with one argument, 42. +// absl::apply(&Foo::Bar, tuple3); +// +// std::tuple<int, int> tuple4(8, 9); +// // Invokes a lambda. +// absl::apply(user_lambda, tuple4); // } template <typename Functor, typename Tuple> auto apply(Functor&& functor, Tuple&& t) @@ -287,7 +317,34 @@ T exchange(T& obj, U&& new_value) { return old_value; } -} // inline namespace lts_2018_12_18 +namespace utility_internal { +template <typename T, typename Tuple, size_t... I> +T make_from_tuple_impl(Tuple&& tup, absl::index_sequence<I...>) { + return T(std::get<I>(std::forward<Tuple>(tup))...); +} +} // namespace utility_internal + +// make_from_tuple +// +// Given the template parameter type `T` and a tuple of arguments +// `std::tuple(arg0, arg1, ..., argN)` constructs an object of type `T` as if by +// calling `T(arg0, arg1, ..., argN)`. +// +// Example: +// +// std::tuple<const char*, size_t> args("hello world", 5); +// auto s = absl::make_from_tuple<std::string>(args); +// assert(s == "hello"); +// +template <typename T, typename Tuple> +constexpr T make_from_tuple(Tuple&& tup) { + return utility_internal::make_from_tuple_impl<T>( + std::forward<Tuple>(tup), + absl::make_index_sequence< + std::tuple_size<absl::decay_t<Tuple>>::value>{}); +} + +} // inline namespace lts_2019_08_08 } // namespace absl #endif // ABSL_UTILITY_UTILITY_H_ |