Mini-Swift

The minimal expression of a Flux architecture in Swift.

Mini is built with be a first class citizen in Swift applications: macOS, iOS and tvOS. With Mini, you can create a thread-safe application with a predictable unidirectional data flow, focusing on what really matters: build awesome applications.

Requirements

• Xcode 10 or later
• Swift 5.0 or later
• iOS 11 or later
• macOS 10.13 or later
• tvOS 11 or later

Installation

Swift Package Manager

• Create a Package.swift file.

// swift-tools-version:5.0

import PackageDescription

let package = Package(
  name: "MiniSwiftProject",
  dependencies: [
    .package(url: "https://github.com/minuscorp/Mini-Swift.git"),
  ],
  targets: [
    .target(name: "MiniSwiftProject", dependencies: ["Mini" /*, "MiniPromises, MiniTasks"*/])
  ]
)

• Mini comes with a bare implementation and two external utility packages in order to ease the usage of the library named MiniTasks and MiniPromises, both dependant on the Mini base or core package.

$ swift build

Cocoapods

• Add this to you Podfile:

pod "Mini-Swift"
# pod "Mini-Swift/MiniPromises"
# pod "Mini-Swift/MiniTasks"

• We also offer two subpecs for logging and testing:

pod "Mini-Swift/Log"
pod "Mini-Swift/Test"

Usage

• MiniSwift is a library which aims the ease of the usage of a Flux oriented architecture for Swift applications. Due its Flux-based nature, it heavily relies on some of its concepts like Store, State, Dispatcher, Action, Task and Reducer.

State

• The minimal unit of the architecture is based on the idea of the State. State is, as its name says, the representation of a part of the application in a moment of time.

• The State is a simple struct which is conformed of different Promises that holds the individual pieces of information that represents the current state, this can be implemented as follows.

• For example:

// If you're using MiniPromises
struct MyCoolState: StateType {
    let cool: Promise<Bool>
}

// If you're using MiniTasks
struct MyCoolState: StateType {
    let cool: Bool?
    let coolTask: AnyTask
}

• The default inner state of a Promise is idle. On the other hand, the default inner state of a Task is idle as well. This means that no Action (see more below), has started any operation over that Promise or Task.

• Both Promise and Task can hold any kind of aditional properties that the developer might encounter useful for its implementation, for example, hold a Date for cache usage:

let promise: Promise<Bool> = .idle()
promise.date = Date()
// Later on...
let date: Date = promise.date

let task: AnyTask = .idle()
task.date = Date()
// Later on...
let date: Date = task.date

• The core idea of a State is its immutability, so once created, no third-party objects are able to mutate it out of the control of the architecture flow.

• As can be seen in the example, a State has a pair of Task + Result usually (that can be any object, if any), which is related with the execution of the Task. In the example above, CoolTask is responsible, through its Reducer to fulfill the Action with the Task result and furthermore, the new State.

• Furthermore, the Promise object unifies the Status + Result tuple, so it can store both the status of an ongoing task and the associated payload produced by it.

Action

• An Action is the piece of information that is being dispatched through the architecture. Any struct can conform to the Action protocol, with the only requirement of being unique its name per application.

struct RequestContactsAccess: Action {
  // As simple as this is.
}

• Actions are free of have some pieces of information attached to them, that's why Mini provides the user with two main utility protocols: CompletableAction, EmptyAction and KeyedPayloadAction.

  • A CompletableAction is a specialization of the Action protocol, which allows the user attach both a Task and some kind of object that gets fulfilled when the Task succeeds.

  struct RequestContactsAccessResult: CompletableAction {
    let promise: Promise<Bool>
  
    typealias Payload = Bool
  }

  • An EmptyAction is a specialization of CompletableAction where the Payload is a Swift.Void, this means it only has associated a Promise<Void>.

  struct ActivateVoucherLoaded: EmptyAction {
    let promise: Promise<Void>
  }

  • A KeyedPayloadAction, adds a Key (which is Hashable) to the CompletableAction. This is a special case where the same Action produces results that can be grouped together, tipically, under a Dictionary (i.e., an Action to search contacts, and grouped by their main phone number).

  struct RequestContactLoadedAction: KeyedCompletableAction {
  
    typealias Payload = CNContact
    typealias Key = String
  
    let promise: [Key: Promise<Payload?>]
  }

We take the advantage of using struct, so all initializers are automatically synthesized.

Examples are done with Promise, but there're equivalent to be used with Tasks.

Store

• A Store is the hub where decissions and side-efects are made through the ingoing and outgoing Actions. A Store is a generic class to inherit from and associate a State for it.

• A Store may produce State changes that can be observed like any other RxSwift's Observable. In this way a View, or any other object of your choice, can receive new States produced by a certain Store.

• A Store reduces the flow of a certain amount of Actions through the var reducerGroup: ReducerGroup property.

• The Store is implemented in a way that has two generic requirements, a State: StateType and a StoreController: Disposable. The StoreController is usually a class that contains the logic to perform the Actions that might be intercepted by the store, i.e, a group of URL requests, perform a database query, etc.

• Through generic specialization, the reducerGroup variable can be rewritten for each case of pair State and StoreController without the need of subclassing the Store.

extension Store where State == TestState, StoreController == TestStoreController {

    var reducerGroup: ReducerGroup {
        return ReducerGroup(
            // Using Promises
            Reducer(of: OneTestAction.self, on: dispatcher) { action in
                self.state = self.state.copy(testPromise: *.value(action.counter))
            },
            // Using Tasks
            Reducer(of: OneTestAction.self, on: dispatcher) { action in
                self.state = self.state.copy(data: *action.payload, dataTask: *action.task)
            }
        )
    }
}

• In the snippet above, we have a complete example of how a Store would work. We use the ReducerGroup to indicate how the Store will intercept Actions of type OneTestAction and that everytime it gets intercepted, the Store's State gets copied (is not black magic 🧙‍, is through a set of Sourcery scripts that are distributed with this package).

If you are using SPM or Carthage, they doesn't really allow to distribute assets with the library, in that regard we recommend to just install Sourcery in your project and use the templates that can be downloaded directly from the repository under the Templates directory.

• When working with Store instances, you may retain a strong reference of its reducerGroup, this is done using the subscribe() method, which is a Disposable that can be used like below:

let bag = DisposeBag()
let store = Store<TestState, TestStoreController>(TestState(), dispatcher: dispatcher, storeController: TestStoreController())
store
    .subscribe()
    .disposed(by: bag)

Dispatcher

• The last piece of the architecture is the Dispatcher. In an application scope, there should be only one Dispatcher alive from which every action is being dispatched.

let action = TestAction()
dispatcher.dispatch(action, mode: .sync)

• With one line, we can notify every Store which has defined a reducer for that type of Action.

Advanced usage

• Mini is built over a request-response unidirectional flow. This is achieved using pair of Action, one for making the request of a change in a certain State, and another Action to mutate the State over the result of the operation being made.

• This is much simplier to explain with a code example:

Using Promises

// We define our state in first place:
struct TestState: StateType {
    // Our state is defined over the Promise of an Integer type.
    let counter: Promise<Int>

    init(counter: Promise<Int> = .idle()) {
        self.counter = counter
    }

    public func isEqual(to other: StateType) -> Bool {
        guard let state = other as? TestState else { return false }
        guard counter == state.counter else { return false }
        return true
    }
}

// We define our actions, one of them represents the request of a change, the other one the response of that change requested.

// This is the request
struct SetCounterAction: Action {
    let counter: Int
}

// This is the response
struct SetCounterActionLoaded: Action {
    let counter: Int
}

// As you can see, both seems to be the same, same parameters, initializer, etc. But next, we define our StoreController.

// The StoreController define the side-effects that an Action might trigger.
class TestStoreController: Disposable {
    
    let dispatcher: Dispatcher
    
    init(dispatcher: Dispatcher) {
        self.dispatcher = dispatcher
    }
    
    // This function dispatches (always in a async mode) the result of the operation, just giving out the number to the dispatcher.
    func counter(_ number: Int) {
        self.dispatcher.dispatch(SetCounterActionLoaded(counter: number), mode: .async)
    }
    
    public func dispose() {
        // NO-OP
    }
}

// Last, but not least, the Store definition with the Reducers
extension Store where State == TestState, StoreController == TestStoreController {

    var reducerGroup: ReducerGroup {
        ReducerGroup(
            // We can use Promises:
            // We set the state with a Promise as .pending, someone has to fill the requirement later on. This represents the Request.
            Reducer(of: SetCounterAction.self, on: self.dispatcher) { action in
                guard !self.state.counter.isOnProgress else { return }
                self.state = TestState(counter: .pending())
                self.storeController.counter(action.counter)
            },
            // Next we receive the Action dispatched by the StoreController with a result, we must fulfill our Promise and notify the store for the State change. This represents the Response.
            Reducer(of: SetCounterActionLoaded.self, on: self.dispatcher) { action in
                self.state.counter
                    .fulfill(action.counter)
                    .notify(to: self)
            }
        )
    }
}

Using Tasks

// We define our state in first place:
struct TestState: StateType {
    // Our state is defined over the Promise of an Integer type.
    let counter: Int?
    let counterTask: AnyTask

    init(counter: Int = nil,
         counterTask: AnyTask = .idle()) {
        self.counter = counter
        self.counterTask = counterTask
    }

    public func isEqual(to other: StateType) -> Bool {
        guard let state = other as? TestState else { return false }
        guard counter == state.counter else { return false }
        guard counterTask == state.counterTask else { return false }
        return true
    }
}

// We define our actions, one of them represents the request of a change, the other one the response of that change requested.

// This is the request
struct SetCounterAction: Action {
    let counter: Int
}

// This is the response
struct SetCounterActionLoaded: Action {
    let counter: Int
    let counterTask: AnyTask
}

// As you can see, both seems to be the same, same parameters, initializer, etc. But next, we define our StoreController.

// The StoreController define the side-effects that an Action might trigger.
class TestStoreController: Disposable {
    
    let dispatcher: Dispatcher
    
    init(dispatcher: Dispatcher) {
        self.dispatcher = dispatcher
    }
    
    // This function dispatches (always in a async mode) the result of the operation, just giving out the number to the dispatcher.
    func counter(_ number: Int) {
        self.dispatcher.dispatch(
            SetCounterActionLoaded(counter: number, 
            counterTask: .success()
            ),
            mode: .async)
    }
    
    public func dispose() {
        // NO-OP
    }
}

// Last, but not least, the Store definition with the Reducers
extension Store where State == TestState, StoreController == TestStoreController {

    var reducerGroup: ReducerGroup {
        ReducerGroup(
            // We can use Tasks:
            // We set the state with a Task as .running, someone has to fill the requirement later on. This represents the Request.
            Reducer(of: SetCounterAction.self, on: dispatcher) { action in
                guard !self.state.counterTask.isRunning else { return }
                self.state = TestState(counterTask: .running())
                self.storeController.counter(action.counter)
            },
            // Next we receive the Action dispatched by the StoreController with a result, we must fulfill our Task and update the data associated with the execution of it on the State. This represents the Response.
            Reducer(of: SetCounterActionLoaded.self, on: dispatcher) { action in
                guard self.state.rawCounterTask.isRunning else { return }
                self.state = TestState(counter: action.counter, counterTask: action.counterTask)
            }
        )
    }
}

Documentation

All the documentation available can be found here

Maintainers

• Jorge Revuelta
• Francisco García Sierra

Authors & Collaborators

• Edilberto Lopez Torregrosa
• Raúl Pedraza León
• Pablo Orgaz
• Sebastián Varela

License

Mini-Swift is available under the Apache 2.0. See the LICENSE file for more info.