2 * Copyright 2014 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.
17 #ifndef FOLLY_GEN_BASE_H
18 #define FOLLY_GEN_BASE_H
22 #include <type_traits>
27 #include <unordered_set>
29 #include "folly/Range.h"
30 #include "folly/Optional.h"
31 #include "folly/Conv.h"
32 #include "folly/gen/Core.h"
35 * Generator-based Sequence Comprehensions in C++, akin to C#'s LINQ
36 * @author Tom Jackson <tjackson@fb.com>
38 * This library makes it possible to write declarative comprehensions for
39 * processing sequences of values efficiently in C++. The operators should be
40 * familiar to those with experience in functional programming, and the
41 * performance will be virtually identical to the equivalent, boilerplate C++
44 * Generator objects may be created from either an stl-like container (anything
45 * supporting begin() and end()), from sequences of values, or from another
46 * generator (see below). To create a generator that pulls values from a vector,
47 * for example, one could write:
49 * vector<string> names { "Jack", "Jill", "Sara", "Tom" };
50 * auto gen = from(names);
52 * Generators are composed by building new generators out of old ones through
53 * the use of operators. These are reminicent of shell pipelines, and afford
54 * similar composition. Lambda functions are used liberally to describe how to
55 * handle individual values:
58 * | mapped([](const fbstring& name) { return name.size(); });
60 * Generators are lazy; they don't actually perform any work until they need to.
61 * As an example, the 'lengths' generator (above) won't actually invoke the
62 * provided lambda until values are needed:
64 * auto lengthVector = lengths | as<std::vector>();
65 * auto totalLength = lengths | sum;
67 * 'auto' is useful in here because the actual types of the generators objects
68 * are usually complicated and implementation-sensitive.
70 * If a simpler type is desired (for returning, as an example), VirtualGen<T>
71 * may be used to wrap the generator in a polymorphic wrapper:
73 * VirtualGen<float> powersOfE() {
74 * return seq(1) | mapped(&expf);
77 * To learn more about this library, including the use of infinite generators,
78 * see the examples in the comments, or the docs (coming soon).
81 namespace folly { namespace gen {
83 class EmptySequence : public std::exception {
85 virtual const char* what() const noexcept {
86 return "This operation cannot be called on an empty sequence";
94 auto operator()(const First& first, const Second& second) const ->
95 decltype(first < second) {
96 return first < second;
102 template<class First,
104 auto operator()(const First& first, const Second& second) const ->
105 decltype(first > second) {
106 return first > second;
113 template<class Value>
114 auto operator()(Value&& value) const ->
115 decltype(std::get<n>(std::forward<Value>(value))) {
116 return std::get<n>(std::forward<Value>(value));
120 template<class Class,
122 class MemberFunction {
124 typedef Result (Class::*MemberPtr)();
128 explicit MemberFunction(MemberPtr member)
132 Result operator()(Class&& x) const {
133 return (x.*member_)();
136 Result operator()(Class& x) const {
137 return (x.*member_)();
141 template<class Class,
143 class ConstMemberFunction{
145 typedef Result (Class::*MemberPtr)() const;
149 explicit ConstMemberFunction(MemberPtr member)
153 Result operator()(const Class& x) const {
154 return (x.*member_)();
158 template<class Class,
162 typedef FieldType (Class::*FieldPtr);
166 explicit Field(FieldPtr field)
170 const FieldType& operator()(const Class& x) const {
174 FieldType& operator()(Class& x) const {
178 FieldType&& operator()(Class&& x) const {
179 return std::move(x.*field_);
185 template<class Value>
186 auto operator()(Value&& value) const ->
187 decltype(std::move(std::forward<Value>(value))) {
188 return std::move(std::forward<Value>(value));
194 template<class Value>
195 auto operator()(Value&& value) const ->
196 decltype(std::forward<Value>(value)) {
197 return std::forward<Value>(value);
201 template <class Dest>
204 template <class Value>
205 Dest operator()(Value&& value) const {
206 return Dest(std::forward<Value>(value));
210 template <class Dest>
213 template <class Value>
214 Dest operator()(Value&& value) const {
215 return ::folly::to<Dest>(std::forward<Value>(value));
219 // Specialization to allow String->StringPiece conversion
221 class To<StringPiece> {
223 StringPiece operator()(StringPiece src) const {
236 template<class Container>
237 struct ValueTypeOfRange {
239 static Container container_;
241 typedef decltype(*std::begin(container_))
243 typedef typename std::decay<decltype(*std::begin(container_))>::type
251 template<class Container,
252 class Value = typename ValueTypeOfRange<Container>::RefType>
253 class ReferencedSource;
255 template<class Value,
256 class Container = std::vector<typename std::decay<Value>::type>>
259 template<class Value, class SequenceImpl>
262 template <class Value>
265 template <class Value, class Distance>
266 class RangeWithStepImpl;
268 template <class Value>
271 template <class Value, class Distance>
272 class SeqWithStepImpl;
274 template <class Value>
277 template<class Value, class Source>
280 template<class Value>
283 template<class Value>
289 template<class Predicate>
292 template<class Predicate>
295 template<class Predicate>
305 template<class Selector, class Comparer = Less>
308 template<class Selector>
311 template<class Operators>
314 template<class Expected>
338 template<class Predicate>
341 template<class Reducer>
346 template<class Selector,
350 template<class Container>
353 template<template<class, class> class Collection = std::vector,
354 template<class> class Allocator = std::allocator>
355 class CollectTemplate;
357 template<class Collection>
360 template<class Value>
361 struct GeneratorBuilder;
363 template<class Needle>
366 template<class Exception,
373 * Polymorphic wrapper
375 template<class Value>
381 template<class Container,
382 class From = detail::ReferencedSource<const Container>>
383 From fromConst(const Container& source) {
384 return From(&source);
387 template<class Container,
388 class From = detail::ReferencedSource<Container>>
389 From from(Container& source) {
390 return From(&source);
393 template<class Container,
395 typename detail::ValueTypeOfRange<Container>::StorageType,
396 class CopyOf = detail::CopiedSource<Value>>
397 CopyOf fromCopy(Container&& source) {
398 return CopyOf(std::forward<Container>(source));
401 template<class Value,
402 class From = detail::CopiedSource<Value>>
403 From from(std::initializer_list<Value> source) {
407 template<class Container,
408 class From = detail::CopiedSource<typename Container::value_type,
410 From from(Container&& source) {
411 return From(std::move(source));
414 template<class Value, class Impl = detail::RangeImpl<Value>,
415 class Gen = detail::Sequence<Value, Impl>>
416 Gen range(Value begin, Value end) {
417 return Gen{std::move(begin), Impl{std::move(end)}};
420 template<class Value, class Distance,
421 class Impl = detail::RangeWithStepImpl<Value, Distance>,
422 class Gen = detail::Sequence<Value, Impl>>
423 Gen range(Value begin, Value end, Distance step) {
424 return Gen{std::move(begin), Impl{std::move(end), std::move(step)}};
427 template<class Value, class Impl = detail::SeqImpl<Value>,
428 class Gen = detail::Sequence<Value, Impl>>
429 Gen seq(Value first, Value last) {
430 return Gen{std::move(first), Impl{std::move(last)}};
433 template<class Value, class Distance,
434 class Impl = detail::SeqWithStepImpl<Value, Distance>,
435 class Gen = detail::Sequence<Value, Impl>>
436 Gen seq(Value first, Value last, Distance step) {
437 return Gen{std::move(first), Impl{std::move(last), std::move(step)}};
440 template<class Value, class Impl = detail::InfiniteImpl<Value>,
441 class Gen = detail::Sequence<Value, Impl>>
442 Gen seq(Value first) {
443 return Gen{std::move(first), Impl{}};
446 template<class Value,
448 class Yield = detail::Yield<Value, Source>>
449 Yield generator(Source&& source) {
450 return Yield(std::forward<Source>(source));
454 * Create inline generator, used like:
456 * auto gen = GENERATOR(int) { yield(1); yield(2); };
458 #define GENERATOR(TYPE) \
459 ::folly::gen::detail::GeneratorBuilder<TYPE>() + \
460 [=](const std::function<void(TYPE)>& yield)
463 * empty() - for producing empty sequences.
465 template<class Value>
466 detail::Empty<Value> empty() {
470 template<class Value>
471 detail::Just<Value> just(Value value) {
472 return detail::Just<Value>(std::move(value));
478 template<class Predicate,
479 class Map = detail::Map<Predicate>>
480 Map mapped(Predicate pred = Predicate()) {
481 return Map(std::move(pred));
484 template<class Predicate,
485 class Map = detail::Map<Predicate>>
486 Map map(Predicate pred = Predicate()) {
487 return Map(std::move(pred));
491 * mapOp - Given a generator of generators, maps the application of the given
492 * operator on to each inner gen. Especially useful in aggregating nested data
495 * chunked(samples, 256)
496 * | mapOp(filter(sampleTest) | count)
499 template<class Operator,
500 class Map = detail::Map<detail::Composer<Operator>>>
501 Map mapOp(Operator op) {
502 return Map(detail::Composer<Operator>(std::move(op)));
506 * member(...) - For extracting a member from each value.
508 * vector<string> strings = ...;
509 * auto sizes = from(strings) | member(&string::size);
511 * If a member is const overridden (like 'front()'), pass template parameter
512 * 'Const' to select the const version, or 'Mutable' to select the non-const
515 * auto heads = from(strings) | member<Const>(&string::front);
522 template<MemberType Constness = Const,
525 class Mem = ConstMemberFunction<Class, Return>,
526 class Map = detail::Map<Mem>>
527 typename std::enable_if<Constness == Const, Map>::type
528 member(Return (Class::*member)() const) {
529 return Map(Mem(member));
532 template<MemberType Constness = Mutable,
535 class Mem = MemberFunction<Class, Return>,
536 class Map = detail::Map<Mem>>
537 typename std::enable_if<Constness == Mutable, Map>::type
538 member(Return (Class::*member)()) {
539 return Map(Mem(member));
543 * field(...) - For extracting a field from each value.
545 * vector<Item> items = ...;
546 * auto names = from(items) | field(&Item::name);
548 * Note that if the values of the generator are rvalues, any non-reference
549 * fields will be rvalues as well. As an example, the code below does not copy
550 * any strings, only moves them:
552 * auto namesVector = from(items)
554 * | field(&Item::name)
557 template<class Class,
559 class Field = Field<Class, FieldType>,
560 class Map = detail::Map<Field>>
561 Map field(FieldType Class::*field) {
562 return Map(Field(field));
565 template<class Predicate,
566 class Filter = detail::Filter<Predicate>>
567 Filter filter(Predicate pred = Predicate()) {
568 return Filter(std::move(pred));
571 template<class Predicate,
572 class All = detail::All<Predicate>>
573 All all(Predicate pred = Predicate()) {
574 return All(std::move(pred));
577 template<class Predicate,
578 class Until = detail::Until<Predicate>>
579 Until until(Predicate pred = Predicate()) {
580 return Until(std::move(pred));
583 template<class Selector,
584 class Comparer = Less,
585 class Order = detail::Order<Selector, Comparer>>
586 Order orderBy(Selector selector = Identity(),
587 Comparer comparer = Comparer()) {
588 return Order(std::move(selector),
589 std::move(comparer));
592 template<class Selector,
593 class Order = detail::Order<Selector, Greater>>
594 Order orderByDescending(Selector selector = Identity()) {
595 return Order(std::move(selector));
598 template<class Selector,
599 class Distinct = detail::Distinct<Selector>>
600 Distinct distinctBy(Selector selector = Identity()) {
601 return Distinct(std::move(selector));
605 class Get = detail::Map<Get<n>>>
610 // construct Dest from each value
611 template <class Dest,
612 class Cast = detail::Map<Cast<Dest>>>
617 // call folly::to on each value
618 template <class Dest,
619 class To = detail::Map<To<Dest>>>
624 template<class Value>
625 detail::TypeAssertion<Value> assert_type() {
634 class FoldLeft = detail::FoldLeft<Seed, Fold>>
635 FoldLeft foldl(Seed seed = Seed(),
636 Fold fold = Fold()) {
637 return FoldLeft(std::move(seed),
641 template<class Reducer,
642 class Reduce = detail::Reduce<Reducer>>
643 Reduce reduce(Reducer reducer = Reducer()) {
644 return Reduce(std::move(reducer));
647 template<class Selector = Identity,
648 class Min = detail::Min<Selector, Less>>
649 Min minBy(Selector selector = Selector()) {
650 return Min(std::move(selector));
653 template<class Selector,
654 class MaxBy = detail::Min<Selector, Greater>>
655 MaxBy maxBy(Selector selector = Selector()) {
656 return MaxBy(std::move(selector));
659 template<class Collection,
660 class Collect = detail::Collect<Collection>>
665 template<template<class, class> class Container = std::vector,
666 template<class> class Allocator = std::allocator,
667 class Collect = detail::CollectTemplate<Container, Allocator>>
672 template<class Collection,
673 class Append = detail::Append<Collection>>
674 Append appendTo(Collection& collection) {
675 return Append(&collection);
678 template<class Needle,
679 class Contains = detail::Contains<typename std::decay<Needle>::type>>
680 Contains contains(Needle&& needle) {
681 return Contains(std::forward<Needle>(needle));
684 template<class Exception,
689 typename std::decay<ErrorHandler>::type>>
690 GuardImpl guard(ErrorHandler&& handler) {
691 return GuardImpl(std::forward<ErrorHandler>(handler));
696 #include "folly/gen/Base-inl.h"
698 #endif // FOLLY_GEN_BASE_H