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- /*
- * Copyright 2016-present Facebook, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * 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
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- #pragma once
- #include <iterator>
- #include <memory>
- #include <folly/CPortability.h>
- #include <folly/portability/SysTypes.h>
- /**
- * Similar to Python's enumerate(), folly::enumerate() can be used to
- * iterate a range with a for-range loop, and it also allows to
- * retrieve the count of iterations so far.
- *
- * For example:
- *
- * for (auto&& it : folly::enumerate(vec)) {
- * // *it is a reference to the current element. Const if vec is const.
- * // it->member can be used as well.
- * // it.index contains the iteration count.
- * }
- *
- * If the iteration variable is const, the reference is too.
- *
- * for (const auto&& it : folly::enumerate(vec)) {
- * // *it is always a const reference.
- * }
- *
- * @author Giuseppe Ottaviano <ott@fb.com>
- */
- namespace folly {
- namespace detail {
- template <class T>
- struct MakeConst {
- using type = const T;
- };
- template <class T>
- struct MakeConst<T&> {
- using type = const T&;
- };
- template <class T>
- struct MakeConst<T*> {
- using type = const T*;
- };
- // Raw pointers don't have an operator->() member function, so the
- // second overload will be SFINAEd out in that case. Otherwise, the
- // second is preferred in the partial order for getPointer(_, 0).
- template <class Iterator>
- FOLLY_ALWAYS_INLINE auto getPointer(const Iterator& it, long)
- -> decltype(std::addressof(*it)) {
- return std::addressof(*it);
- }
- template <class Iterator>
- FOLLY_ALWAYS_INLINE auto getPointer(const Iterator& it, int)
- -> decltype(it.operator->()) {
- return it.operator->();
- }
- template <class Iterator>
- class Enumerator {
- public:
- explicit Enumerator(Iterator it) : it_(std::move(it)) {}
- class Proxy {
- public:
- using difference_type = ssize_t;
- using value_type = typename std::iterator_traits<Iterator>::value_type;
- using reference = typename std::iterator_traits<Iterator>::reference;
- using pointer = typename std::iterator_traits<Iterator>::pointer;
- using iterator_category = std::input_iterator_tag;
- FOLLY_ALWAYS_INLINE explicit Proxy(const Enumerator& e)
- : it_(e.it_), index(e.idx_) {}
- // Non-const Proxy: Forward constness from Iterator.
- FOLLY_ALWAYS_INLINE reference operator*() {
- return *it_;
- }
- FOLLY_ALWAYS_INLINE pointer operator->() {
- return getPointer(it_, 0);
- }
- // Const Proxy: Force const references.
- FOLLY_ALWAYS_INLINE typename MakeConst<reference>::type operator*() const {
- return *it_;
- }
- FOLLY_ALWAYS_INLINE typename MakeConst<pointer>::type operator->() const {
- return getPointer(it_, 0);
- }
- private:
- const Iterator& it_;
- public:
- const size_t index;
- };
- FOLLY_ALWAYS_INLINE Proxy operator*() const {
- return Proxy(*this);
- }
- FOLLY_ALWAYS_INLINE Enumerator& operator++() {
- ++it_;
- ++idx_;
- return *this;
- }
- template <typename OtherIterator>
- FOLLY_ALWAYS_INLINE bool operator==(
- const Enumerator<OtherIterator>& rhs) const {
- return it_ == rhs.it_;
- }
- template <typename OtherIterator>
- FOLLY_ALWAYS_INLINE bool operator!=(
- const Enumerator<OtherIterator>& rhs) const {
- return !(it_ == rhs.it_);
- }
- private:
- template <typename OtherIterator>
- friend class Enumerator;
- Iterator it_;
- size_t idx_ = 0;
- };
- template <class Range>
- class RangeEnumerator {
- Range r_;
- using BeginIteratorType = decltype(std::declval<Range>().begin());
- using EndIteratorType = decltype(std::declval<Range>().end());
- public:
- explicit RangeEnumerator(Range&& r) : r_(std::forward<Range>(r)) {}
- Enumerator<BeginIteratorType> begin() {
- return Enumerator<BeginIteratorType>(r_.begin());
- }
- Enumerator<EndIteratorType> end() {
- return Enumerator<EndIteratorType>(r_.end());
- }
- };
- } // namespace detail
- template <class Range>
- detail::RangeEnumerator<Range> enumerate(Range&& r) {
- return detail::RangeEnumerator<Range>(std::forward<Range>(r));
- }
- } // namespace folly
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