2 * Copyright 2017 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
18 #define FOLLY_GEN_BASE_H_
24 #include <type_traits>
25 #include <unordered_map>
26 #include <unordered_set>
30 #include <folly/Conv.h>
31 #include <folly/Optional.h>
32 #include <folly/Range.h>
33 #include <folly/Utility.h>
34 #include <folly/gen/Core.h>
37 * Generator-based Sequence Comprehensions in C++, akin to C#'s LINQ
38 * @author Tom Jackson <tjackson@fb.com>
40 * This library makes it possible to write declarative comprehensions for
41 * processing sequences of values efficiently in C++. The operators should be
42 * familiar to those with experience in functional programming, and the
43 * performance will be virtually identical to the equivalent, boilerplate C++
46 * Generator objects may be created from either an stl-like container (anything
47 * supporting begin() and end()), from sequences of values, or from another
48 * generator (see below). To create a generator that pulls values from a vector,
49 * for example, one could write:
51 * vector<string> names { "Jack", "Jill", "Sara", "Tom" };
52 * auto gen = from(names);
54 * Generators are composed by building new generators out of old ones through
55 * the use of operators. These are reminicent of shell pipelines, and afford
56 * similar composition. Lambda functions are used liberally to describe how to
57 * handle individual values:
60 * | mapped([](const fbstring& name) { return name.size(); });
62 * Generators are lazy; they don't actually perform any work until they need to.
63 * As an example, the 'lengths' generator (above) won't actually invoke the
64 * provided lambda until values are needed:
66 * auto lengthVector = lengths | as<std::vector>();
67 * auto totalLength = lengths | sum;
69 * 'auto' is useful in here because the actual types of the generators objects
70 * are usually complicated and implementation-sensitive.
72 * If a simpler type is desired (for returning, as an example), VirtualGen<T>
73 * may be used to wrap the generator in a polymorphic wrapper:
75 * VirtualGen<float> powersOfE() {
76 * return seq(1) | mapped(&expf);
79 * To learn more about this library, including the use of infinite generators,
80 * see the examples in the comments, or the docs (coming soon).
88 template <class First, class Second>
89 auto operator()(const First& first, const Second& second) const ->
90 decltype(first < second) {
91 return first < second;
97 template <class First, class Second>
98 auto operator()(const First& first, const Second& second) const ->
99 decltype(first > second) {
100 return first > second;
107 template <class Value>
108 auto operator()(Value&& value) const ->
109 decltype(std::get<n>(std::forward<Value>(value))) {
110 return std::get<n>(std::forward<Value>(value));
114 template <class Class, class Result>
115 class MemberFunction {
117 typedef Result (Class::*MemberPtr)();
121 explicit MemberFunction(MemberPtr member)
125 Result operator()(Class&& x) const {
126 return (x.*member_)();
129 Result operator()(Class& x) const {
130 return (x.*member_)();
133 Result operator()(Class* x) const {
134 return (x->*member_)();
138 template <class Class, class Result>
139 class ConstMemberFunction{
141 typedef Result (Class::*MemberPtr)() const;
145 explicit ConstMemberFunction(MemberPtr member)
149 Result operator()(const Class& x) const {
150 return (x.*member_)();
153 Result operator()(const Class* x) const {
154 return (x->*member_)();
158 template <class Class, class FieldType>
161 typedef FieldType (Class::*FieldPtr);
165 explicit Field(FieldPtr field)
169 const FieldType& operator()(const Class& x) const {
173 const FieldType& operator()(const Class* x) const {
177 FieldType& operator()(Class& x) const {
181 FieldType& operator()(Class* x) const {
185 FieldType&& operator()(Class&& x) const {
186 return std::move(x.*field_);
192 template <class Value>
193 auto operator()(Value&& value) const ->
194 decltype(std::move(std::forward<Value>(value))) {
195 return std::move(std::forward<Value>(value));
200 * Class and helper function for negating a boolean Predicate
202 template <class Predicate>
209 explicit Negate(Predicate pred)
210 : pred_(std::move(pred))
214 bool operator()(Arg&& arg) const {
215 return !pred_(std::forward<Arg>(arg));
218 template <class Predicate>
219 Negate<Predicate> negate(Predicate pred) {
220 return Negate<Predicate>(std::move(pred));
223 template <class Dest>
226 template <class Value>
227 Dest operator()(Value&& value) const {
228 return Dest(std::forward<Value>(value));
232 template <class Dest>
235 template <class Value>
236 Dest operator()(Value&& value) const {
237 return ::folly::to<Dest>(std::forward<Value>(value));
241 // Specialization to allow String->StringPiece conversion
243 class To<StringPiece> {
245 StringPiece operator()(StringPiece src) const {
250 template <class Key, class Value>
255 template <class Self>
261 template <class Container>
262 struct ValueTypeOfRange {
264 using RefType = decltype(*std::begin(std::declval<Container&>()));
265 using StorageType = typename std::decay<RefType>::type;
274 class Value = typename ValueTypeOfRange<Container>::RefType>
275 class ReferencedSource;
279 class Container = std::vector<typename std::decay<Value>::type>>
282 template <class Value, class SequenceImpl>
285 template <class Value>
288 template <class Value, class Distance>
289 class RangeWithStepImpl;
291 template <class Value>
294 template <class Value, class Distance>
295 class SeqWithStepImpl;
297 template <class Value>
300 template <class Value, class Source>
303 template <class Value>
306 template <class Value>
307 class SingleReference;
309 template <class Value>
315 template <class Predicate>
318 template <class Predicate>
321 template <class Predicate>
328 template <class Rand>
333 template <class Selector, class Comparer = Less>
336 template <class Selector>
339 template <class Selector>
342 template <class Operators>
345 template <class Expected>
352 template <bool forever>
364 template <class Seed, class Fold>
369 template <bool result>
372 template <class Reducer>
377 template <class Selector, class Comparer>
380 template <class Container>
384 template <class, class> class Collection = std::vector,
385 template <class> class Allocator = std::allocator>
386 class CollectTemplate;
388 template <class Collection>
391 template <class Value>
392 struct GeneratorBuilder;
394 template <class Needle>
397 template <class Exception, class ErrorHandler>
408 * Polymorphic wrapper
410 template <class Value>
418 class From = detail::ReferencedSource<const Container>>
419 From fromConst(const Container& source) {
420 return From(&source);
423 template <class Container, class From = detail::ReferencedSource<Container>>
424 From from(Container& source) {
425 return From(&source);
430 class Value = typename detail::ValueTypeOfRange<Container>::StorageType,
431 class CopyOf = detail::CopiedSource<Value>>
432 CopyOf fromCopy(Container&& source) {
433 return CopyOf(std::forward<Container>(source));
436 template <class Value, class From = detail::CopiedSource<Value>>
437 From from(std::initializer_list<Value> source) {
444 detail::CopiedSource<typename Container::value_type, Container>>
445 From from(Container&& source) {
446 return From(std::move(source));
451 class Impl = detail::RangeImpl<Value>,
452 class Gen = detail::Sequence<Value, Impl>>
453 Gen range(Value begin, Value end) {
454 return Gen{std::move(begin), Impl{std::move(end)}};
460 class Impl = detail::RangeWithStepImpl<Value, Distance>,
461 class Gen = detail::Sequence<Value, Impl>>
462 Gen range(Value begin, Value end, Distance step) {
463 return Gen{std::move(begin), Impl{std::move(end), std::move(step)}};
468 class Impl = detail::SeqImpl<Value>,
469 class Gen = detail::Sequence<Value, Impl>>
470 Gen seq(Value first, Value last) {
471 return Gen{std::move(first), Impl{std::move(last)}};
477 class Impl = detail::SeqWithStepImpl<Value, Distance>,
478 class Gen = detail::Sequence<Value, Impl>>
479 Gen seq(Value first, Value last, Distance step) {
480 return Gen{std::move(first), Impl{std::move(last), std::move(step)}};
485 class Impl = detail::InfiniteImpl<Value>,
486 class Gen = detail::Sequence<Value, Impl>>
487 Gen seq(Value first) {
488 return Gen{std::move(first), Impl{}};
491 template <class Value, class Source, class Yield = detail::Yield<Value, Source>>
492 Yield generator(Source&& source) {
493 return Yield(std::forward<Source>(source));
497 * Create inline generator, used like:
499 * auto gen = GENERATOR(int) { yield(1); yield(2); };
501 #define GENERATOR(TYPE) \
502 ::folly::gen::detail::GeneratorBuilder<TYPE>() + \
503 [=](const std::function<void(TYPE)>& yield)
506 * empty() - for producing empty sequences.
508 template <class Value>
509 detail::Empty<Value> empty() {
515 class Just = typename std::conditional<
516 std::is_reference<Value>::value,
517 detail::SingleReference<typename std::remove_reference<Value>::type>,
518 detail::SingleCopy<Value>>::type>
519 Just just(Value&& value) {
520 return Just(std::forward<Value>(value));
526 template <class Predicate, class Map = detail::Map<Predicate>>
527 Map mapped(Predicate pred = Predicate()) {
528 return Map(std::move(pred));
531 template <class Predicate, class Map = detail::Map<Predicate>>
532 Map map(Predicate pred = Predicate()) {
533 return Map(std::move(pred));
537 * mapOp - Given a generator of generators, maps the application of the given
538 * operator on to each inner gen. Especially useful in aggregating nested data
541 * chunked(samples, 256)
542 * | mapOp(filter(sampleTest) | count)
545 template <class Operator, class Map = detail::Map<detail::Composer<Operator>>>
546 Map mapOp(Operator op) {
547 return Map(detail::Composer<Operator>(std::move(op)));
551 * member(...) - For extracting a member from each value.
553 * vector<string> strings = ...;
554 * auto sizes = from(strings) | member(&string::size);
556 * If a member is const overridden (like 'front()'), pass template parameter
557 * 'Const' to select the const version, or 'Mutable' to select the non-const
560 * auto heads = from(strings) | member<Const>(&string::front);
568 * These exist because MSVC has problems with expression SFINAE in templates
569 * assignment and comparisons don't work properly without being pulled out
570 * of the template declaration
572 template <MemberType Constness>
575 value = Constness == Const
579 template <MemberType Constness>
580 struct ExprIsMutable {
582 value = Constness == Mutable
587 MemberType Constness = Const,
590 class Mem = ConstMemberFunction<Class, Return>,
591 class Map = detail::Map<Mem>>
592 typename std::enable_if<ExprIsConst<Constness>::value, Map>::type
593 member(Return (Class::*member)() const) {
594 return Map(Mem(member));
598 MemberType Constness = Mutable,
601 class Mem = MemberFunction<Class, Return>,
602 class Map = detail::Map<Mem>>
603 typename std::enable_if<ExprIsMutable<Constness>::value, Map>::type
604 member(Return (Class::*member)()) {
605 return Map(Mem(member));
609 * field(...) - For extracting a field from each value.
611 * vector<Item> items = ...;
612 * auto names = from(items) | field(&Item::name);
614 * Note that if the values of the generator are rvalues, any non-reference
615 * fields will be rvalues as well. As an example, the code below does not copy
616 * any strings, only moves them:
618 * auto namesVector = from(items)
620 * | field(&Item::name)
626 class Field = Field<Class, FieldType>,
627 class Map = detail::Map<Field>>
628 Map field(FieldType Class::*field) {
629 return Map(Field(field));
632 template <class Predicate = Identity, class Filter = detail::Filter<Predicate>>
633 Filter filter(Predicate pred = Predicate()) {
634 return Filter(std::move(pred));
637 template <class Predicate, class Until = detail::Until<Predicate>>
638 Until until(Predicate pred = Predicate()) {
639 return Until(std::move(pred));
643 class Selector = Identity,
644 class Comparer = Less,
645 class Order = detail::Order<Selector, Comparer>>
646 Order orderBy(Selector selector = Selector(),
647 Comparer comparer = Comparer()) {
648 return Order(std::move(selector),
649 std::move(comparer));
653 class Selector = Identity,
654 class Order = detail::Order<Selector, Greater>>
655 Order orderByDescending(Selector selector = Selector()) {
656 return Order(std::move(selector));
659 template <class Selector = Identity, class GroupBy = detail::GroupBy<Selector>>
660 GroupBy groupBy(Selector selector = Selector()) {
661 return GroupBy(std::move(selector));
665 class Selector = Identity,
666 class Distinct = detail::Distinct<Selector>>
667 Distinct distinctBy(Selector selector = Selector()) {
668 return Distinct(std::move(selector));
671 template <int n, class Get = detail::Map<Get<n>>>
676 // construct Dest from each value
677 template <class Dest, class Cast = detail::Map<Cast<Dest>>>
682 // call folly::to on each value
683 template <class Dest, class To = detail::Map<To<Dest>>>
688 template <class Value>
689 detail::TypeAssertion<Value> assert_type() {
698 * any() - For determining if any value in a sequence satisfies a predicate.
700 * The following is an example for checking if any computer is broken:
702 * bool schrepIsMad = from(computers) | any(isBroken);
704 * (because everyone knows Schrep hates broken computers).
706 * Note that if no predicate is provided, 'any()' checks if any of the values
707 * are true when cased to bool. To check if any of the scores are nonZero:
709 * bool somebodyScored = from(scores) | any();
711 * Note: Passing an empty sequence through 'any()' will always return false. In
712 * fact, 'any()' is equivilent to the composition of 'filter()' and 'notEmpty'.
714 * from(source) | any(pred) == from(source) | filter(pred) | notEmpty
718 class Predicate = Identity,
719 class Filter = detail::Filter<Predicate>,
720 class NotEmpty = detail::IsEmpty<false>,
721 class Composed = detail::Composed<Filter, NotEmpty>>
722 Composed any(Predicate pred = Predicate()) {
723 return Composed(Filter(std::move(pred)), NotEmpty());
727 * all() - For determining whether all values in a sequence satisfy a predicate.
729 * The following is an example for checking if all members of a team are cool:
731 * bool isAwesomeTeam = from(team) | all(isCool);
733 * Note that if no predicate is provided, 'all()'' checks if all of the values
734 * are true when cased to bool.
735 * The following makes sure none of 'pointers' are nullptr:
737 * bool allNonNull = from(pointers) | all();
739 * Note: Passing an empty sequence through 'all()' will always return true. In
740 * fact, 'all()' is equivilent to the composition of 'filter()' with the
741 * reversed predicate and 'isEmpty'.
743 * from(source) | all(pred) == from(source) | filter(negate(pred)) | isEmpty
747 class Predicate = Identity,
748 class Filter = detail::Filter<Negate<Predicate>>,
749 class IsEmpty = detail::IsEmpty<true>,
750 class Composed = detail::Composed<Filter, IsEmpty>>
751 Composed all(Predicate pred = Predicate()) {
752 return Composed(Filter(std::move(negate(pred))), IsEmpty());
755 template <class Seed, class Fold, class FoldLeft = detail::FoldLeft<Seed, Fold>>
756 FoldLeft foldl(Seed seed = Seed(),
757 Fold fold = Fold()) {
758 return FoldLeft(std::move(seed),
762 template <class Reducer, class Reduce = detail::Reduce<Reducer>>
763 Reduce reduce(Reducer reducer = Reducer()) {
764 return Reduce(std::move(reducer));
767 template <class Selector = Identity, class Min = detail::Min<Selector, Less>>
768 Min minBy(Selector selector = Selector()) {
769 return Min(std::move(selector));
772 template <class Selector, class MaxBy = detail::Min<Selector, Greater>>
773 MaxBy maxBy(Selector selector = Selector()) {
774 return MaxBy(std::move(selector));
777 template <class Collection, class Collect = detail::Collect<Collection>>
783 template <class, class> class Container = std::vector,
784 template <class> class Allocator = std::allocator,
785 class Collect = detail::CollectTemplate<Container, Allocator>>
790 template <class Collection, class Append = detail::Append<Collection>>
791 Append appendTo(Collection& collection) {
792 return Append(&collection);
797 class Contains = detail::Contains<typename std::decay<Needle>::type>>
798 Contains contains(Needle&& needle) {
799 return Contains(std::forward<Needle>(needle));
806 detail::GuardImpl<Exception, typename std::decay<ErrorHandler>::type>>
807 GuardImpl guard(ErrorHandler&& handler) {
808 return GuardImpl(std::forward<ErrorHandler>(handler));
813 class UnwrapOr = detail::UnwrapOr<typename std::decay<Fallback>::type>>
814 UnwrapOr unwrapOr(Fallback&& fallback) {
815 return UnwrapOr(std::forward<Fallback>(fallback));
820 #include <folly/gen/Base-inl.h>