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// 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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