Abseil Common Libraries (C++) (grcp 依赖)
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219 lines
6.9 KiB
219 lines
6.9 KiB
// Copyright 2017 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// http://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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// |
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// This header file contains C++11 versions of standard <utility> header |
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// abstractions available within C++14 and C++17, and are designed to be drop-in |
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// replacement for code compliant with C++14 and C++17. |
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// |
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// The following abstractions are defined: |
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// |
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// * integer_sequence<T, Ints...> == std::integer_sequence<T, Ints...> |
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// * index_sequence<Ints...> == std::index_sequence<Ints...> |
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// * make_integer_sequence<T, N> == std::make_integer_sequence<T, N> |
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// * make_index_sequence<N> == std::make_index_sequence<N> |
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// * index_sequence_for<Ts...> == std::index_sequence_for<Ts...> |
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// |
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// This header file also provides the tag types `in_place_t`, `in_place_type_t`, |
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// and `in_place_index_t`, as well as the constant `in_place`, and |
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// `constexpr` `std::move()` and `std::forward()` implementations in C++11. |
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// |
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// References: |
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// |
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// http://en.cppreference.com/w/cpp/utility/integer_sequence |
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// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3658.html |
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// |
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// |
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// Example: |
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// // Unpack a tuple for use as a function call's argument list. |
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// |
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// template <typename F, typename Tup, size_t... Is> |
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// auto Impl(F f, const Tup& tup, absl::index_sequence<Is...>) |
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// -> decltype(f(std::get<Is>(tup) ...)) { |
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// return f(std::get<Is>(tup) ...); |
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// } |
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// |
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// template <typename Tup> |
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// using TupIdxSeq = absl::make_index_sequence<std::tuple_size<Tup>::value>; |
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// |
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// template <typename F, typename Tup> |
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// auto ApplyFromTuple(F f, const Tup& tup) |
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// -> decltype(Impl(f, tup, TupIdxSeq<Tup>{})) { |
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// return Impl(f, tup, TupIdxSeq<Tup>{}); |
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// } |
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#ifndef ABSL_UTILITY_UTILITY_H_ |
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#define ABSL_UTILITY_UTILITY_H_ |
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#include <cstddef> |
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#include <cstdlib> |
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#include <utility> |
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#include "absl/base/config.h" |
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#include "absl/meta/type_traits.h" |
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namespace absl { |
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// integer_sequence |
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// |
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// Class template representing a compile-time integer sequence. An instantiation |
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// of `integer_sequence<T, Ints...>` has a sequence of integers encoded in its |
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// type through its template arguments (which is a common need when |
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// working with C++11 variadic templates). `absl::integer_sequence` is designed |
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// to be a drop-in replacement for C++14's `std::integer_sequence`. |
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// |
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// Example: |
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// |
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// template< class T, T... Ints > |
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// void user_function(integer_sequence<T, Ints...>); |
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// |
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// int main() |
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// { |
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// // user_function's `T` will be deduced to `int` and `Ints...` |
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// // will be deduced to `0, 1, 2, 3, 4`. |
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// user_function(make_integer_sequence<int, 5>()); |
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// } |
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template <typename T, T... Ints> |
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struct integer_sequence { |
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using value_type = T; |
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static constexpr size_t size() noexcept { return sizeof...(Ints); } |
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}; |
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// index_sequence |
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// |
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// A helper template for an `integer_sequence` of `size_t`, |
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// `absl::index_sequence` is designed to be a drop-in replacement for C++14's |
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// `std::index_sequence`. |
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template <size_t... Ints> |
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using index_sequence = integer_sequence<size_t, Ints...>; |
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namespace utility_internal { |
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template <typename Seq, size_t SeqSize, size_t Rem> |
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struct Extend; |
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// Note that SeqSize == sizeof...(Ints). It's passed explicitly for efficiency. |
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template <typename T, T... Ints, size_t SeqSize> |
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struct Extend<integer_sequence<T, Ints...>, SeqSize, 0> { |
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using type = integer_sequence<T, Ints..., (Ints + SeqSize)...>; |
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}; |
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template <typename T, T... Ints, size_t SeqSize> |
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struct Extend<integer_sequence<T, Ints...>, SeqSize, 1> { |
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using type = integer_sequence<T, Ints..., (Ints + SeqSize)..., 2 * SeqSize>; |
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}; |
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// Recursion helper for 'make_integer_sequence<T, N>'. |
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// 'Gen<T, N>::type' is an alias for 'integer_sequence<T, 0, 1, ... N-1>'. |
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template <typename T, size_t N> |
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struct Gen { |
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using type = |
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typename Extend<typename Gen<T, N / 2>::type, N / 2, N % 2>::type; |
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}; |
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template <typename T> |
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struct Gen<T, 0> { |
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using type = integer_sequence<T>; |
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}; |
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} // namespace utility_internal |
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// Compile-time sequences of integers |
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// make_integer_sequence |
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// |
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// This template alias is equivalent to |
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// `integer_sequence<int, 0, 1, ..., N-1>`, and is designed to be a drop-in |
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// replacement for C++14's `std::make_integer_sequence`. |
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template <typename T, T N> |
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using make_integer_sequence = typename utility_internal::Gen<T, N>::type; |
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// make_index_sequence |
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// |
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// This template alias is equivalent to `index_sequence<0, 1, ..., N-1>`, |
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// and is designed to be a drop-in replacement for C++14's |
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// `std::make_index_sequence`. |
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template <size_t N> |
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using make_index_sequence = make_integer_sequence<size_t, N>; |
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// index_sequence_for |
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// |
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// Converts a typename pack into an index sequence of the same length, and |
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// is designed to be a drop-in replacement for C++14's |
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// `std::index_sequence_for()` |
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template <typename... Ts> |
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using index_sequence_for = make_index_sequence<sizeof...(Ts)>; |
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// Tag types |
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#ifdef ABSL_HAVE_STD_OPTIONAL |
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using std::in_place_t; |
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using std::in_place; |
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#else // ABSL_HAVE_STD_OPTIONAL |
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// in_place_t |
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// |
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// Tag type used to specify in-place construction, such as with |
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// `absl::optional`, designed to be a drop-in replacement for C++17's |
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// `std::in_place_t`. |
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struct in_place_t {}; |
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extern const in_place_t in_place; |
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#endif // ABSL_HAVE_STD_OPTIONAL |
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#ifdef ABSL_HAVE_STD_ANY |
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using std::in_place_type_t; |
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#else |
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// in_place_type_t |
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// |
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// Tag type used for in-place construction when the type to construct needs to |
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// be specified, such as with `absl::any`, designed to be a drop-in replacement |
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// for C++17's `std::in_place_type_t`. |
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template <typename T> |
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struct in_place_type_t {}; |
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#endif // ABSL_HAVE_STD_ANY |
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// in_place_index_t |
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// |
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// Tag type used for in-place construction when the type to construct needs to |
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// be specified, such as with `absl::any`, designed to be a drop-in replacement |
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// for C++17's `std::in_place_index_t`. |
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template <size_t I> |
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struct in_place_index_t {}; |
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// Constexpr move and forward |
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// move() |
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// |
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// A constexpr version of `std::move()`, designed to be a drop-in replacement |
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// for C++14's `std::move()`. |
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template <typename T> |
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constexpr absl::remove_reference_t<T>&& move(T&& t) noexcept { |
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return static_cast<absl::remove_reference_t<T>&&>(t); |
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} |
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// forward() |
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// |
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// A constexpr version of `std::forward()`, designed to be a drop-in replacement |
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// for C++14's `std::forward()`. |
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template <typename T> |
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constexpr T&& forward( |
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absl::remove_reference_t<T>& t) noexcept { // NOLINT(runtime/references) |
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return static_cast<T&&>(t); |
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} |
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} // namespace absl |
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#endif // ABSL_UTILITY_UTILITY_H_
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