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166 lines
4.1 KiB
C
166 lines
4.1 KiB
C
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/*
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* Copyright 2016 Facebook, Inc.
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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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#pragma once
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#include <iterator>
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#include <memory>
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#include <folly/portability/SysTypes.h>
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/*
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* Similar to Python's enumerate(), folly::enumerate() can be used to
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* iterate a range with a for-range loop, and it also allows to
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* retrieve the count of iterations so far.
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*
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* For example:
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*
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* for (auto it : folly::enumerate(vec)) {
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* // *it is a reference to the current element. Const if vec is const.
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* // it->member can be used as well.
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* // it.index contains the iteration count.
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* }
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*
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* If the iteration variable is const, the reference is too.
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*
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* for (const auto it : folly::enumerate(vec)) {
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* // *it is always a const reference.
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* }
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*
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* @author Giuseppe Ottaviano <ott@fb.com>
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*/
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namespace folly {
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namespace detail {
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template <class T>
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struct MakeConst {
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using type = const T;
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};
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template <class T>
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struct MakeConst<T&> {
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using type = const T&;
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};
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template <class T>
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struct MakeConst<T*> {
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using type = const T*;
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};
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// Raw pointers don't have an operator->() member function, so the
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// second overload will be SFINAEd out in that case. Otherwise, the
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// second is preferred in the partial order for getPointer(_, 0).
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template <class Iterator>
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auto getPointer(const Iterator& it, long) -> decltype(std::addressof(*it)) {
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return std::addressof(*it);
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}
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template <class Iterator>
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auto getPointer(const Iterator& it, int) -> decltype(it.operator->()) {
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return it.operator->();
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}
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template <class Iterator>
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class Enumerator {
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public:
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explicit Enumerator(Iterator it) : it_(std::move(it)) {}
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class Proxy {
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public:
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using difference_type = ssize_t;
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using value_type = typename std::iterator_traits<Iterator>::value_type;
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using reference = typename std::iterator_traits<Iterator>::reference;
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using pointer = typename std::iterator_traits<Iterator>::pointer;
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using iterator_category = std::input_iterator_tag;
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explicit Proxy(const Enumerator* e) : it_(e->it_), index(e->idx_) {}
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// Non-const Proxy: Forward constness from Iterator.
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reference operator*() {
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return *it_;
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}
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pointer operator->() {
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return getPointer(it_, 0);
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}
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// Const Proxy: Force const references.
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typename MakeConst<reference>::type operator*() const {
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return *it_;
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}
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typename MakeConst<pointer>::type operator->() const {
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return getPointer(it_, 0);
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}
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private:
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const Iterator& it_;
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public:
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const size_t index;
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};
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Proxy operator*() const {
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return Proxy(this);
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}
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Enumerator& operator++() {
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++it_;
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++idx_;
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return *this;
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}
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template <typename OtherIterator>
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bool operator==(const Enumerator<OtherIterator>& rhs) {
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return it_ == rhs.it_;
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}
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template <typename OtherIterator>
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bool operator!=(const Enumerator<OtherIterator>& rhs) {
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return !(*this == rhs);
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}
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private:
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template <typename OtherIterator>
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friend class Enumerator;
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Iterator it_;
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size_t idx_ = 0;
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};
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template <class Range>
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class RangeEnumerator {
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Range r_;
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using BeginIteratorType = decltype(std::declval<Range>().begin());
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using EndIteratorType = decltype(std::declval<Range>().end());
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public:
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explicit RangeEnumerator(Range&& r) : r_(std::forward<Range>(r)) {}
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Enumerator<BeginIteratorType> begin() {
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return Enumerator<BeginIteratorType>(r_.begin());
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}
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Enumerator<EndIteratorType> end() {
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return Enumerator<EndIteratorType>(r_.end());
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}
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};
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} // namespace detail
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template <class Range>
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detail::RangeEnumerator<Range> enumerate(Range&& r) {
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return detail::RangeEnumerator<Range>(std::forward<Range>(r));
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}
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} // namespace folly
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