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https://github.com/inamiy/harvest

🌾 Harvest: Apple's Combine.framework + State Machine, inspired by Elm.
https://github.com/inamiy/harvest

automaton combine-framework elm redux state-machine swift

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🌾 Harvest: Apple's Combine.framework + State Machine, inspired by Elm.

Host: GitHub
URL: https://github.com/inamiy/harvest
Owner: inamiy
License: mit
Archived: true
Created: 2019-06-07T00:51:39.000Z (over 5 years ago)
Default Branch: master
Last Pushed: 2021-12-12T05:04:14.000Z (almost 3 years ago)
Last Synced: 2024-05-22T15:32:53.375Z (4 months ago)
Topics: automaton, combine-framework, elm, redux, state-machine, swift
Language: Swift
Homepage:
Size: 298 KB
Stars: 384
Watchers: 4
Forks: 11
Open Issues: 3
Metadata Files:
- Readme: README.md
- License: LICENSE

Awesome Lists containing this project

README

        ## NOTE: This repository has been discontinued in favor of [Actomaton](https://github.com/inamiy/Actomaton).

# 🌾 Harvest

[![Swift 5.1](https://img.shields.io/badge/swift-5.1-orange.svg?style=flat)](https://swift.org/download/)

![Build Status](https://github.com/inamiy/Harvest/workflows/CI/badge.svg)

Apple's [Combine.framework](https://developer.apple.com/documentation/combine) (from iOS 13) + State Machine, inspired by [Elm](http://elm-lang.org/).

This is a sister library of the following projects:

- [ReactiveAutomaton](https://github.com/inamiy/ReactiveAutomaton) (using [ReactiveSwift](https://github.com/ReactiveCocoa/ReactiveSwift))

- [RxAutomaton](https://github.com/inamiy/RxAutomaton) (using [RxSwift](https://github.com/ReactiveX/RxSwift))

## Requirement

Xcode 11 (Swift 5.1 / macOS 10.15, iOS 13, ...)

## Example

![](Assets/login-diagram.png)

To make a state transition diagram like above _with additional effects_, follow these steps:

### 1. Define `State`s and `Input`s

```swift

// 1. Define `State`s and `Input`s.

enum State {

    case loggedOut, loggingIn, loggedIn, loggingOut

}

enum Input {

    case login, loginOK, logout, logoutOK

    case forceLogout

}

```

### 2. Define `EffectQueue`

```swift

enum EffectQueue: EffectQueueProtocol {

    case `default`

    case request

    var flattenStrategy: FlattenStrategy {

        switch self {

        case .default: return .merge

        case .request: return .latest

        }

    }

    static var defaultEffectQueue: EffectQueue {

        .default

    }

}

```

`EffectQueue` allows additional side-effects (`Effect`, a wrapper of `Publisher`) to be scheduled with a specific `FlattenStrategy`, such as `flatMap` (`.merge`), `flatMapLatest` (`.latest`), etc.

In above case, we want to automatically cancel previous network requests if occurred multiple times, so we also prepare `case request` queue with `.latest` strategy.

### 3. Create `EffectMapping` (Effect-wise reducer)

```swift

// NOTE: `EffectID` is useful for manual effect cancellation, but not used in this example.

typealias EffectID = Never

typealias Harvester = Harvest.Harvester

typealias EffectMapping = Harvester.EffectMapping

typealias Effect = Harvester.Effect

// Additional effects while state-transitioning.

let loginOKPublisher = /* show UI, setup DB, request APIs, ..., and send `Input.loginOK` */

let logoutOKPublisher = /* show UI, clear cache, cancel APIs, ..., and send `Input.logoutOK` */

let forceLogoutOKPublisher = /* do something more special, ..., and send `Input.logoutOK` */

let canForceLogout: (State) -> Bool = [.loggingIn, .loggedIn].contains

let mappings: [EffectMapping] = [

  /*  Input   |   fromState => toState     |      Effect       */

  /* ----------------------------------------------------------*/

    .login    | .loggedOut  => .loggingIn  | Effect(loginOKPublisher, queue: .request),

    .loginOK  | .loggingIn  => .loggedIn   | .empty,

    .logout   | .loggedIn   => .loggingOut | Effect(logoutOKPublisher, queue: .request),

    .logoutOK | .loggingOut => .loggedOut  | .empty,

    .forceLogout | canForceLogout => .loggingOut | Effect(forceLogoutOKPublisher, queue: .request)

]

```

`EffectMapping` is Redux's `Reducer` or Elm's `Update` pure function that also returns `Effect` during the state-transition.

Note that `queue: .request` is specified so that those effects will be handled in the same queue with `.latest` strategy.

Instead of writing it as a plain function with pattern-matching, you can also write in a fancy markdown-table-like syntax as shown above.

### 4. Setup `Harvester` (state machine)

```swift

// Prepare input pipe for sending `Input` to `Harvester`.

let inputs = PassthroughSubject()

var cancellables: [AnyCancellable] = []

// Setup state machine.

let harvester = Harvester(

    state: .loggedOut,

    input: inputs,

    mapping: .reduce(.first, mappings),  // combine mappings using `reduce` helper

    scheduler: DispatchQueue.main

)

// Observe state-transition replies (`.success` or `.failure`).

harvester.replies.sink { reply in

    print("received reply = \(reply)")

}.store(in: &cancellables)

// Observe current state changes.

harvester.state.sink { state in

    print("current state = \(state)")

}.store(in: &cancellables)

```

NOTE: `func reduce` is declared to combine multiple `mappings` into one.

### 5. And let's test!

```swift

let send = inputs.send

expect(harvester.state) == .loggedIn    // already logged in

send(Input.logout)

expect(harvester.state) == .loggingOut  // logging out...

// `logoutOKPublisher` will automatically send `Input.logoutOK` later

// and transit to `State.loggedOut`.

expect(harvester.state) == .loggedOut   // already logged out

send(Input.login)

expect(harvester.state) == .loggingIn   // logging in...

// `loginOKPublisher` will automatically send `Input.loginOK` later

// and transit to `State.loggedIn`.

// 👨🏽 < But wait, there's more!

// Let's send `Input.forceLogout` immediately after `State.loggingIn`.

send(Input.forceLogout)                       // 💥💣💥

expect(harvester.state) == .loggingOut  // logging out...

// `forceLogoutOKublisher` will automatically send `Input.logoutOK` later

// and transit to `State.loggedOut`.

```

Please notice how state-transitions, effect calls and cancellation are nicely performed.

If your cancellation strategy is more complex than just using `FlattenStrategy.latest`, you can also use `Effect.cancel` to manually stop specific `EffectID`.

Note that **any sizes of `State` and `Input` will work using `Harvester`**, from single state (like above example) to covering whole app's states (like React.js + Redux architecture).

## Using `Feedback` effect model as alternative

Instead of using `EffectMapping` with fine-grained `EffectQueue` model, Harvest also supports `Feedback` system as described in the following libraries:

- [NoTests/RxFeedback](https://github.com/NoTests/RxFeedback.swift)

- [Babylonpartners/ReactiveFeedback](https://github.com/Babylonpartners/ReactiveFeedback)

- [sergdort/CombineFeedback](https://github.com/sergdort/CombineFeedback)

See [inamiy/ReactiveAutomaton#12](https://github.com/inamiy/ReactiveAutomaton/pull/12) for more discussion.

## Composable Architecture with SwiftUI

[Pull Request \#8](https://github.com/inamiy/Harvest/pull/8) introduced `HarvestStore` and `HarvestOptics` frameworks for Composable Architecture, especially focused on SwiftUI.

- **HarvestStore**: 2-way bindable `Store` optimized for SwiftUI

- **HarvestOptics**: Input & state lifting helpers using [FunOptics](https://github.com/inamiy/FunOptics)

See [Harvest-SwiftUI-Gallery](https://github.com/inamiy/Harvest-SwiftUI-Gallery) for the examples.

See also [Babylonpartners/ios-playbook#171](https://github.com/Babylonpartners/ios-playbook/pull/171) for further related discussion.

- [ ] TODO: Write documentation

## References

1. [ReactiveAutomaton](https://github.com/inamiy/ReactiveAutomaton) (using [ReactiveSwift](https://github.com/ReactiveCocoa/ReactiveSwift))

1. [RxAutomaton](https://github.com/inamiy/RxAutomaton) (using [RxSwift](https://github.com/ReactiveX/RxSwift))

1. [iOSDC 2016 (Tokyo, in Japanese)](https://iosdc.jp/2016/) (2016/08/20)

    - [iOSDC Japan 2016 08/20 Track A / Reactive State Machine / 稲見 泰宏 - YouTube](https://www.youtube.com/watch?v=Yvz9H9AWGFM) (video)

    - [Reactive State Machine (Japanese) // Speaker Deck](https://speakerdeck.com/inamiy/reactive-state-machine-japanese) (slide)

1. [iOSConf SG (Singapore, in English)](http://iosconf.sg/) (2016/10/20-21)

    - [Reactive State Machine - iOS Conf SG 2016 - YouTube](https://www.youtube.com/watch?v=Oau4JjJP3nA) (video)

    - [Reactive State Machine // Speaker Deck](https://speakerdeck.com/inamiy/reactive-state-machine-1) (slide)

## License

[MIT](LICENSE)