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- /*
- * Copyright 2011-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 <folly/Portability.h>
- #include <folly/Preprocessor.h>
- #include <type_traits>
- namespace folly {
- /**
- * @function for_each
- *
- * folly::for_each is a generalized iteration algorithm. Example:
- *
- * auto one = std::make_tuple(1, 2, 3);
- * auto two = std::vector<int>{1, 2, 3};
- * auto func = [](auto element, auto index) {
- * cout << index << " : " << element << endl;
- * };
- * folly::for_each(one, func);
- * folly::for_each(two, func);
- *
- * The for_each function allows iteration through sequences, these can either be
- * runtime sequences (i.e. entities for which std::begin and std::end work) or
- * compile time sequences (as deemed by the presence of std::tuple_length<> and
- * member get<> or ADL get<> functions).
- *
- * If a sequence type is both a runtime sequence (aka range) and a compile-time
- * sequence (aka tuple), then it is treated as a range in preference to a tuple.
- * An example of such a type is std::array.
- *
- * The function is made to provide a convenient library based alternative to the
- * proposal p0589r0, which aims to generalize the range based for loop even
- * further to work with compile time sequences.
- *
- * A drawback of using range based for loops is that sometimes you do not have
- * access to the index within the range. This provides easy access to that, even
- * with compile time sequences.
- *
- * And breaking out is easy:
- *
- * auto range_one = std::vector<int>{1, 2, 3};
- * auto range_two = std::make_tuple(1, 2, 3);
- * auto func = [](auto ele, auto index) {
- * cout << "Element at index " << index << " : " << ele;
- * if (index == 1) {
- * return folly::loop_break;
- * }
- * return folly::loop_continue;
- * };
- * folly_for_each(range_one, func);
- * folly_for_each(range_two, func);
- *
- * A simple use case would be when using futures, if the user was doing calls to
- * n servers then they would accept the callback with the futures like this:
- *
- * auto vec = std::vector<std::future<int>>{request_one(), ...};
- * when_all(vec.begin(), vec.end()).then([](auto futures) {
- * folly::for_each(futures, [](auto& fut) { ... });
- * });
- *
- * Now when this code switches to use tuples instead of the runtime std::vector,
- * then the loop does not need to change, the code will still work just fine:
- *
- * when_all(future_one, future_two, future_three).then([](auto futures) {
- * folly::for_each(futures, [](auto& fut) { ... });
- * });
- */
- template <typename Range, typename Func>
- FOLLY_CPP14_CONSTEXPR Func for_each(Range&& range, Func func);
- /**
- * The user should return loop_break and loop_continue if they want to iterate
- * in such a way that they can preemptively stop the loop and break out when
- * certain conditions are met.
- */
- namespace for_each_detail {
- enum class LoopControl : bool { BREAK, CONTINUE };
- } // namespace for_each_detail
- constexpr auto loop_break = for_each_detail::LoopControl::BREAK;
- constexpr auto loop_continue = for_each_detail::LoopControl::CONTINUE;
- /**
- * Utility method to help access elements of a sequence with one uniform
- * interface.
- *
- * This can be useful for example when you are looping through a sequence and
- * want to modify another sequence based on the information in the current
- * sequence:
- *
- * auto range_one = std::make_tuple(1, 2, 3);
- * auto range_two = std::make_tuple(4, 5, 6);
- * folly::for_each(range_one, [&range_two](auto ele, auto index) {
- * folly::fetch(range_two, index) = ele;
- * });
- *
- * For ranges, this works by first trying to use the iterator class if the
- * iterator has been marked to be a random access iterator. This should be
- * inspectable via the std::iterator_traits traits class. If the iterator class
- * is not present or is not a random access iterator then the implementation
- * falls back to trying to use the indexing operator (operator[]) to fetch the
- * required element.
- */
- template <typename Sequence, typename Index>
- FOLLY_CPP14_CONSTEXPR decltype(auto) fetch(Sequence&& sequence, Index&& index);
- } // namespace folly
- /**
- * Everything below is deprecated.
- */
- /*
- * Form a local variable name from "FOR_EACH_" x __LINE__, so that
- * FOR_EACH can be nested without creating shadowed declarations.
- */
- #define _FE_ANON(x) FB_CONCATENATE(FOR_EACH_, FB_CONCATENATE(x, __LINE__))
- /*
- * If you just want the element values, please use:
- *
- * for (auto&& element : collection)
- *
- * If you need access to the iterators please write an explicit iterator loop
- */
- #define FOR_EACH(i, c) \
- if (bool _FE_ANON(s1_) = false) { \
- } else \
- for (auto&& _FE_ANON(s2_) = (c); !_FE_ANON(s1_); _FE_ANON(s1_) = true) \
- for (auto i = _FE_ANON(s2_).begin(); i != _FE_ANON(s2_).end(); ++i)
- /*
- * If you just want the element values, please use this (ranges-v3) construct:
- *
- * for (auto&& element : collection | view::reverse)
- *
- * If you need access to the iterators please write an explicit iterator loop
- */
- #define FOR_EACH_R(i, c) \
- if (bool _FE_ANON(s1_) = false) { \
- } else \
- for (auto&& _FE_ANON(s2_) = (c); !_FE_ANON(s1_); _FE_ANON(s1_) = true) \
- for (auto i = _FE_ANON(s2_).rbegin(); i != _FE_ANON(s2_).rend(); ++i)
- /*
- * If you just want the element values, please use this construct:
- *
- * for (auto&& element : folly::enumerate(collection))
- *
- * If you need access to the iterators please write an explicit iterator loop
- * and use a counter variable
- */
- #define FOR_EACH_ENUMERATE(count, i, c) \
- if (bool _FE_ANON(s1_) = false) { \
- } else \
- for (auto&& FOR_EACH_state2 = (c); !_FE_ANON(s1_); _FE_ANON(s1_) = true) \
- if (size_t _FE_ANON(n1_) = 0) { \
- } else if (const size_t& count = _FE_ANON(n1_)) { \
- } else \
- for (auto i = FOR_EACH_state2.begin(); i != FOR_EACH_state2.end(); \
- ++_FE_ANON(n1_), ++i)
- /**
- * If you just want the keys, please use this (ranges-v3) construct:
- *
- * for (auto&& element : collection | view::keys)
- *
- * If you just want the values, please use this (ranges-v3) construct:
- *
- * for (auto&& element : collection | view::values)
- *
- * If you need to see both, use:
- *
- * for (auto&& element : collection) {
- * auto const& key = element.first;
- * auto& value = element.second;
- * ......
- * }
- *
- */
- #define FOR_EACH_KV(k, v, c) \
- if (unsigned int _FE_ANON(s1_) = 0) { \
- } else \
- for (auto&& _FE_ANON(s2_) = (c); !_FE_ANON(s1_); _FE_ANON(s1_) = 1) \
- for (auto _FE_ANON(s3_) = _FE_ANON(s2_).begin(); \
- _FE_ANON(s3_) != _FE_ANON(s2_).end(); \
- _FE_ANON(s1_) == 2 ? ((_FE_ANON(s1_) = 0), ++_FE_ANON(s3_)) \
- : (_FE_ANON(s3_) = _FE_ANON(s2_).end())) \
- for (auto& k = _FE_ANON(s3_)->first; !_FE_ANON(s1_); ++_FE_ANON(s1_)) \
- for (auto& v = _FE_ANON(s3_)->second; !_FE_ANON(s1_); ++_FE_ANON(s1_))
- namespace folly {
- namespace detail {
- // Boost 1.48 lacks has_less, we emulate a subset of it here.
- template <typename T, typename U>
- class HasLess {
- struct BiggerThanChar {
- char unused[2];
- };
- template <typename C, typename D>
- static char test(decltype(C() < D())*);
- template <typename, typename>
- static BiggerThanChar test(...);
- public:
- enum { value = sizeof(test<T, U>(nullptr)) == 1 };
- };
- /**
- * notThereYet helps the FOR_EACH_RANGE macro by opportunistically
- * using "<" instead of "!=" whenever available when checking for loop
- * termination. This makes e.g. examples such as FOR_EACH_RANGE (i,
- * 10, 5) execute zero iterations instead of looping virtually
- * forever. At the same time, some iterator types define "!=" but not
- * "<". The notThereYet function will dispatch differently for those.
- *
- * Below is the correct implementation of notThereYet. It is disabled
- * because of a bug in Boost 1.46: The filesystem::path::iterator
- * defines operator< (via boost::iterator_facade), but that in turn
- * uses distance_to which is undefined for that particular
- * iterator. So HasLess (defined above) identifies
- * boost::filesystem::path as properly comparable with <, but in fact
- * attempting to do so will yield a compile-time error.
- *
- * The else branch (active) contains a conservative
- * implementation.
- */
- #if 0
- template <class T, class U>
- typename std::enable_if<HasLess<T, U>::value, bool>::type
- notThereYet(T& iter, const U& end) {
- return iter < end;
- }
- template <class T, class U>
- typename std::enable_if<!HasLess<T, U>::value, bool>::type
- notThereYet(T& iter, const U& end) {
- return iter != end;
- }
- #else
- template <class T, class U>
- typename std::enable_if<
- (std::is_arithmetic<T>::value && std::is_arithmetic<U>::value) ||
- (std::is_pointer<T>::value && std::is_pointer<U>::value),
- bool>::type
- notThereYet(T& iter, const U& end) {
- return iter < end;
- }
- template <class T, class U>
- typename std::enable_if<
- !((std::is_arithmetic<T>::value && std::is_arithmetic<U>::value) ||
- (std::is_pointer<T>::value && std::is_pointer<U>::value)),
- bool>::type
- notThereYet(T& iter, const U& end) {
- return iter != end;
- }
- #endif
- /**
- * downTo is similar to notThereYet, but in reverse - it helps the
- * FOR_EACH_RANGE_R macro.
- */
- template <class T, class U>
- typename std::enable_if<HasLess<U, T>::value, bool>::type downTo(
- T& iter,
- const U& begin) {
- return begin < iter--;
- }
- template <class T, class U>
- typename std::enable_if<!HasLess<U, T>::value, bool>::type downTo(
- T& iter,
- const U& begin) {
- if (iter == begin) {
- return false;
- }
- --iter;
- return true;
- }
- } // namespace detail
- } // namespace folly
- /*
- * Look at the Ranges-v3 views and you'll probably find an easier way to build
- * the view you want but the equivalent is roughly:
- *
- * for (auto& element : make_iterator_range(begin, end))
- */
- #define FOR_EACH_RANGE(i, begin, end) \
- for (auto i = (true ? (begin) : (end)); \
- ::folly::detail::notThereYet(i, (end)); \
- ++i)
- /*
- * Look at the Ranges-v3 views and you'll probably find an easier way to build
- * the view you want but the equivalent is roughly:
- *
- * for (auto& element : make_iterator_range(begin, end) | view::reverse)
- */
- #define FOR_EACH_RANGE_R(i, begin, end) \
- for (auto i = (false ? (begin) : (end)); ::folly::detail::downTo(i, (begin));)
- #include <folly/container/Foreach-inl.h>
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