> For the complete documentation index, see [llms.txt](https://presto95.gitbook.io/combine-rxswift-reactiveswift/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://presto95.gitbook.io/combine-rxswift-reactiveswift/publisher.md).

# Publisher

Publisher는 시간이 지남에 따라 값의 시퀀스를 전달할 수 있다.

Combine에서 `Publisher`는 프로토콜로 정의되어 있으며, 다음의 타입이 이 프로토콜을 채택한다.

* `Publishers` 열거형의 중첩 타입으로 정의된 여러 구조체
* `Just`, `Empty`와 같은 Convenience Publisher
* 타입을 지운 Publisher인 `AnyPublisher` 구조체
* 등등

두 개의 연관 타입이 정의되어 있다.

* 첫 번째 연관 타입은 값의 타입(`Output`)이다.
* 두 번째 연관 타입은 에러의 타입(`Failure`)이다. 
  * 에러의 타입은 `Error` 프로토콜을 채택해야 한다.

`Publisher` 프로토콜의 익스텐션으로 여러 오퍼레이터*operator*가 정의되어 있으며, 이를 사용해서 이벤트 처리 체인을 구성할 수 있다.

각 오퍼레이터는 `Publisher` 프로토콜을 구현하는 타입을 반환한다.

기본적으로 `Publisher` 프로토콜은 오퍼레이터의 이름과 그것이 반환하는 Publisher의 이름을 비슷하게 만들어 두었으나, 이 프로토콜을 채택하는 개별 Publisher는 오퍼레이터가 다른 타입의 Publisher를 반환하게 구현해둘 수 있다.

```swift
protocol Publisher { }

extension Publisher {
  func count() -> Publishers.Count<Self>
}

struct Just: Publisher {
  func count() -> Just<Int>
}
```

`Publisher` 프로토콜의 익스텐션으로 여러 오퍼레이터가 구현되어 있으나, `Just`와 같은 개별 Publisher가 오퍼레이터를 오버로딩하여 다른 타입을 반환하도록 구현한 경우를 어렵지 않게 찾아볼 수 있다.

## RxSwift

일반적으로 `Publisher` 프로토콜을 구현하는 타입은 RxSwift의 `Observable`과 비교 가능하다.

에러 연관 타입이 `Never`로 에러 값을 전달하지 않는다는 것이 보장되는 것은 RxCocoa의 `Driver`와 비교 가능하다.

하나의 값을 전달하고 종료하거나, 에러를 내고 종료하는 `Single`의 동작은 Combine의 `Future` Publisher를 사용하여 구현할 수 있다.

`Completable`, `Maybe`와 같은 RxSwift의 Traits는 Combine에 별도의 타입으로 구현되어 있지 않다.

## ReactiveSwift

일반적으로 `Publisher` 프로토콜을 구현하는 타입은 ReactiveSwift의 `SignalProducer`와 `Signal`과 비교 가능하다.

`SignalProducer`는 'Cold Observable', `Signal`은 'Hot Observable'을 의미하는데, Combine에서는 이 동작을 별도의 타입으로 구분하지 않는다.

## Publisher와 Operator 쌍

### Convenience Publishers

| Publisher                                                        | 관련 Operator |
| ---------------------------------------------------------------- | ----------- |
| [Future](/combine-rxswift-reactiveswift/publisher/future.md)     | -           |
| [Just](/combine-rxswift-reactiveswift/publisher/just.md)         | -           |
| [Deferred](/combine-rxswift-reactiveswift/publisher/deferred.md) | -           |
| [Empty](/combine-rxswift-reactiveswift/publisher/empty.md)       | -           |
| [Fail](/combine-rxswift-reactiveswift/publisher/fail.md)         | -           |
| Record                                                           | -           |

### Publisher in Publishers Enum

#### Convenience Publishers

| Publisher                                                        | 관련 Operator |
| ---------------------------------------------------------------- | ----------- |
| [Sequence](/combine-rxswift-reactiveswift/publisher/sequence.md) | -           |
| [Catch](/combine-rxswift-reactiveswift/publisher/catch.md)       | `catch`     |

#### Working with Subscribers

| Publisher                                                              | 관련 Operator |
| ---------------------------------------------------------------------- | ----------- |
| [ReceiveOn](/combine-rxswift-reactiveswift/publisher/receiveon.md)     | `receive`   |
| [SubscribeOn](/combine-rxswift-reactiveswift/publisher/subscribeon.md) | `subscribe` |

#### Mapping Elements

| Publisher                                                                    | 관련 Operator                                    |
| ---------------------------------------------------------------------------- | ---------------------------------------------- |
| [TryScan](/combine-rxswift-reactiveswift/publisher/tryscan.md)               | `tryScan`                                      |
| [TryMap](/combine-rxswift-reactiveswift/publisher/trymap.md)                 | `tryMap`                                       |
| FlatMap                                                                      | `flatMap`                                      |
| [Map](/combine-rxswift-reactiveswift/publisher/map.md)                       | `map` / `replaceNil` / `combineLatest` / `zip` |
| [MapError](/combine-rxswift-reactiveswift/publisher/maperror.md)             | `mapError`                                     |
| [Scan](/combine-rxswift-reactiveswift/publisher/scan.md)                     | `scan`                                         |
| [SetFailureType](/combine-rxswift-reactiveswift/publisher/setfailuretype.md) | `setFailureType`                               |

#### Filtering Elements

| Publisher                                                                              | 관련 Operator           |
| -------------------------------------------------------------------------------------- | --------------------- |
| [CompactMap](/combine-rxswift-reactiveswift/publisher/compactmap.md)                   | `compactMap`          |
| [Filter](/combine-rxswift-reactiveswift/publisher/filter.md)                           | `filter`              |
| [RemoveDuplicates](/combine-rxswift-reactiveswift/publisher/removeduplicates.md)       | `removeDuplicates`    |
| [ReplaceEmpty](/combine-rxswift-reactiveswift/publisher/replaceempty.md)               | `replaceEmpty`        |
| [ReplaceError](/combine-rxswift-reactiveswift/publisher/replaceerror.md)               | `replaceError`        |
| [TryCompactMap](/combine-rxswift-reactiveswift/publisher/trycompactmap.md)             | `tryCompactMap`       |
| [TryFilter](/combine-rxswift-reactiveswift/publisher/tryfilter.md)                     | `tryFilter`           |
| [TryRemoveDuplicates](/combine-rxswift-reactiveswift/publisher/tryremoveduplicates.md) | `tryRemoveDuplicates` |

#### Reducing Elements

| Publisher                                                                                                                                    | 관련 Operator    |
| -------------------------------------------------------------------------------------------------------------------------------------------- | -------------- |
| [Collect](/combine-rxswift-reactiveswift/publisher/collect.md)                                                                               | `collect`      |
| [CollectByCount](/combine-rxswift-reactiveswift/publisher/collectbycount.md)                                                                 | `collect`      |
| [CollectByTime](/combine-rxswift-reactiveswift/publisher/collectbytime.md)                                                                   | `collect`      |
| [IgnoreOutput](/combine-rxswift-reactiveswift/publisher/ignoreoutput.md)                                                                     | `ignoreOutput` |
| [Reduce](https://github.com/presto95/Combine-RxSwift-ReactiveSwift/tree/a9a4a8aa03a4a3e56527cbbe7168b6c19ab16ebb/Publisher/Reduce/README.md) | `reduce`       |
| [TryReduce](/combine-rxswift-reactiveswift/publisher/tryreduce.md)                                                                           | `tryReduce`    |

#### Applying Mathematical Operations on Elements

| Publisher                                                                  | 관련 Operator         |
| -------------------------------------------------------------------------- | ------------------- |
| [Comparison](/combine-rxswift-reactiveswift/publisher/comparison.md)       | `max` / `min`       |
| [TryComparison](/combine-rxswift-reactiveswift/publisher/trycomparison.md) | `tryMax` / `tryMin` |
| [Count](/combine-rxswift-reactiveswift/publisher/count.md)                 | `count`             |

#### Applying Matching Criteria to Elements

| Publisher                                                                        | 관련 Operator     |
| -------------------------------------------------------------------------------- | --------------- |
| [TryAllSatisfy](/combine-rxswift-reactiveswift/publisher/tryallsatisfy.md)       | `tryAllSatisfy` |
| [AllSatisfy](/combine-rxswift-reactiveswift/publisher/allsatisfy.md)             | `allSatisfy`    |
| [Contains](/combine-rxswift-reactiveswift/publisher/contains.md)                 | `contains`      |
| [ContainsWhere](/combine-rxswift-reactiveswift/publisher/containswhere.md)       | `contains`      |
| [TryContainsWhere](/combine-rxswift-reactiveswift/publisher/trycontainswhere.md) | `tryContains`   |

#### Applying Sequence Operations to Elements

| Publisher                                                                                                                                             | 관련 Operator          |
| ----------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------- |
| [FirstWhere](/combine-rxswift-reactiveswift/publisher/firstwhere.md)                                                                                  | `first`              |
| [LastWhere](/combine-rxswift-reactiveswift/publisher/lastwhere.md)                                                                                    | `last`               |
| [DropUntilOutput](/combine-rxswift-reactiveswift/publisher/dropuntiloutput.md)                                                                        | `drop`               |
| [DropWhile](/combine-rxswift-reactiveswift/publisher/dropwhile.md)                                                                                    | `drop`               |
| [TryDropWhile](/combine-rxswift-reactiveswift/publisher/trydropwhile.md)                                                                              | `tryDrop`            |
| [Concatenate](/combine-rxswift-reactiveswift/publisher/concatenate.md)                                                                                | `append` / `prepend` |
| [Drop](/combine-rxswift-reactiveswift/publisher/drop.md)                                                                                              | `dropFirst`          |
| [PrefixUntilOutput](/combine-rxswift-reactiveswift/publisher/prefixuntiloutput.md)                                                                    | `prefix`             |
| [PrefixWhile](/combine-rxswift-reactiveswift/publisher/prefixwhile.md)                                                                                | `prefix`             |
| [First](/combine-rxswift-reactiveswift/publisher/first.md)                                                                                            | `first`              |
| [Last](/combine-rxswift-reactiveswift/publisher/last.md)                                                                                              | `last`               |
| [TryFirstWhere](/combine-rxswift-reactiveswift/publisher/tryfirstwhere.md)                                                                            | `tryFirst`           |
| [TryLastWhere](/combine-rxswift-reactiveswift/publisher/trylastwhere.md)                                                                              | `tryLast`            |
| [TryPrefixWhile](https://github.com/presto95/Combine-RxSwift-ReactiveSwift/tree/a9a4a8aa03a4a3e56527cbbe7168b6c19ab16ebb/Publisher/TryPrefixWhere.md) | `tryPrefix`          |
| [Output](/combine-rxswift-reactiveswift/publisher/output.md)                                                                                          | `output`             |

#### Combining Elements from Multiple Publishers

| Publisher                                                                    | 관련 Operator     |
| ---------------------------------------------------------------------------- | --------------- |
| [CombineLatest](/combine-rxswift-reactiveswift/publisher/combinelatest.md)   | `combineLatest` |
| [CombineLatest3](/combine-rxswift-reactiveswift/publisher/combinelatest3.md) | `combineLatest` |
| [CombineLatest4](/combine-rxswift-reactiveswift/publisher/combinelatest4.md) | `combineLatest` |
| [Merge](/combine-rxswift-reactiveswift/publisher/merge.md)                   | `merge`         |
| [Merge3](/combine-rxswift-reactiveswift/publisher/merge3.md)                 | `merge`         |
| [Merge4](/combine-rxswift-reactiveswift/publisher/merge4.md)                 | `merge`         |
| [Merge5](/combine-rxswift-reactiveswift/publisher/merge5.md)                 | `merge`         |
| [Merge6](/combine-rxswift-reactiveswift/publisher/merge6.md)                 | `merge`         |
| [Merge7](/combine-rxswift-reactiveswift/publisher/merge7.md)                 | `merge`         |
| [Merge8](/combine-rxswift-reactiveswift/publisher/merge8.md)                 | `merge`         |
| [MergeMany](/combine-rxswift-reactiveswift/publisher/mergemany.md)           | `merge`         |
| [Zip](/combine-rxswift-reactiveswift/publisher/zip.md)                       | `zip`           |
| [Zip3](/combine-rxswift-reactiveswift/publisher/zip3.md)                     | `zip`           |
| [Zip4](/combine-rxswift-reactiveswift/publisher/zip4.md)                     | `zip`           |

#### Handling Errors

| Publisher                                                                      | 관련 Operator       |
| ------------------------------------------------------------------------------ | ----------------- |
| [AssertNoFailure](/combine-rxswift-reactiveswift/publisher/assertnofailure.md) | `assertNoFailure` |
| [Catch](/combine-rxswift-reactiveswift/publisher/catch.md)                     | `catch`           |
| [TryCatch](/combine-rxswift-reactiveswift/publisher/trycatch.md)               | `tryCatch`        |
| [Retry](/combine-rxswift-reactiveswift/publisher/retry.md)                     | `retry`           |

#### Adapting Publisher Types

| Publisher                                                                    | 관련 Operator      |
| ---------------------------------------------------------------------------- | ---------------- |
| [SwitchToLatest](/combine-rxswift-reactiveswift/publisher/switchtolatest.md) | `switchToLatest` |

#### Controlling Timing

| Publisher                                                                      | 관련 Operator       |
| ------------------------------------------------------------------------------ | ----------------- |
| [Debounce](/combine-rxswift-reactiveswift/publisher/debounce.md)               | `debounce`        |
| [Delay](/combine-rxswift-reactiveswift/publisher/delay.md)                     | `delay`           |
| [MeasureInterval](/combine-rxswift-reactiveswift/publisher/measureinterval.md) | `measureInterval` |
| [Throttle](/combine-rxswift-reactiveswift/publisher/throttle.md)               | `throttle`        |
| [Timeout](/combine-rxswift-reactiveswift/publisher/timeout.md)                 | `timeout`         |

#### Creating Reference-type Publishers

| Publisher | 관련 Operator |
| --------- | ----------- |
| Share     | `share`     |

#### Encoding and Decoding

| Publisher                                                    | 관련 Operator |
| ------------------------------------------------------------ | ----------- |
| [Encode](/combine-rxswift-reactiveswift/publisher/encode.md) | `encode`    |
| [Decode](/combine-rxswift-reactiveswift/publisher/decode.md) | `decode`    |

#### Identifying Properties with Key Paths

| Publisher                                                              | 관련 Operator |
| ---------------------------------------------------------------------- | ----------- |
| [MapKeyPath](/combine-rxswift-reactiveswift/publisher/mapkeypath.md)   | `map`       |
| [MapKeyPath2](/combine-rxswift-reactiveswift/publisher/mapkeypath2.md) | `map`       |
| [MapKeyPath3](/combine-rxswift-reactiveswift/publisher/mapkeypath3.md) | `map`       |

#### Using Explicit Publisher Connections

| Publisher   | 관련 Operator   |
| ----------- | ------------- |
| Autoconnect | `autoconnect` |

#### Working with Multiple Subscribers

| Publisher | 관련 Operator |
| --------- | ----------- |
| Multicast | `multicast` |

#### Buffering Elements

| Publisher | 관련 Operator |
| --------- | ----------- |
| Buffer    | `buffer`    |

#### Adding Explicit Connectability

| Publisher       | 관련 Operator       |
| --------------- | ----------------- |
| MakeConnectable | `makeConnectable` |

#### Debugging

| Publisher                                                                | 관련 Operator                        |
| ------------------------------------------------------------------------ | ---------------------------------- |
| [Breakpoint](/combine-rxswift-reactiveswift/publisher/breakpoint.md)     | `breakpoint` / `breakpointOnError` |
| [HandleEvents](/combine-rxswift-reactiveswift/publisher/handleevents.md) | `handleEvents`                     |
| [Print](/combine-rxswift-reactiveswift/publisher/print.md)               | `print`                            |

### Misc.

| Publisher                                                                                                | 관련 Operator           |
| -------------------------------------------------------------------------------------------------------- | --------------------- |
| [AnyPublisher](/combine-rxswift-reactiveswift/publisher/anypublisher.md)                                 | `eraseToAnyPublisher` |
| NotificationCenter.Publisher                                                                             | -                     |
| [Optional.Publisher](/combine-rxswift-reactiveswift/publisher/optional.publisher.md)                     | -                     |
| [Result.Publisher](/combine-rxswift-reactiveswift/publisher/result.publisher.md)                         | -                     |
| [URLSession.DataTaskPublisher](/combine-rxswift-reactiveswift/publisher/urlsession.datataskpublisher.md) | -                     |
| Timer.TimerPublisher                                                                                     | -                     |