Bindy

Just a simple bindings.

Installation

Add pod 'Bindy'

to your podfile, and run pod install

SPM is supported too.

Usage

For now, Bindy has a couple of basic types

• Signal - allows triggering a callback when some signal received.
• Observable - allows observing changing of value.
• ObservableArray - conforms to MutableCollection protocol, so you can work with it like with a regular array: subscript index, replace objects, map, enumerate, etc... Also, ObservableArray has updates signal, which will notify you about any changes in the array, such as insert, replace, delete.

Observables Sample (updated with property wrappers)

@Observable var firstname = "Salvador"
@Observable var age = 54

func setupBindings() {
    $age.bind(self) { [unowned self] newAge in
            print("Happy \(newAge) birthday, \(firstname)")
    }
    age = 55
}

Don't forget always use [unowned owner] in closure to prevent the retain cycle.

Signal and Array Sample

let messages: ObservableArray<Message> = []
let newMessage = Signal<Message>()
    
func setupBindings() {
    newMessage.bind(self) { [unowned self] message in
            self.messages.append(message)
    }
    
    messages.updates.bind(self) { [unowned tableView] updates in
            self.tableView.pefrom(updates: updates)     
       }
}
       
func handleDidRecieveMessage(_ message: Message) {
     newMessage.send(message)      
    }
}

You don't need to remove binding manually if you don't want. When the object that you pass as owner in bind(_ owner: AnyObject... method deallocates, corresponding bindings will clean. However, if you want to unbind manually, just call unbind(_ owner: AnyObject). Bindy has an extension for tableView for performing updates tableView.perform(updates:...

Also, observables have a method observe(_ owner: AnyObject..., it works like bind, but triggers callback immediately, this may be more comfortable in some situations.

Transformations

If you want to receive events with transformed type, you can use transform function on Observables like:

let speed = Observable(20)
lazy var speedString = speed.transform { "\($0)km/h" }
    
func setupBindings() {
    speedString.observe(self) { [unowned self] speedString in
        // speedString = "20km/h"
            self.speedLabel.text = speedString
        }
}

Combinations

You can combine two Observable types with combined(with: ..., transform: ...) function like:

let firstname = Observable("Maxim")
let lastname = Observable("Kotliar")
let age = Observable(24)

lazy var fullName = firstname
            .combined(with: lastname) { "name: \($0) \($1)" }
            .combined(with: age) { "\($0), age: \($1)" }

func setupBindings() {
    userInfo.observe(self) { [unowned self] info in
            // info = "name: Maxim Kotliar, age:24"
            self.userInfoLabel.text = info
        }
}

For Observable<Bool> combinations Bindy have more convenient operators && and ||, so you can combine Observable<Bool> like regular Bool, also you can invert it with !:

let isPremiumPurchased = Observable(true)
let isInTrialPeriodEnded = Observable(false)
let isAdsShowForced = Observable(false)

lazy var shouldShowAds = isAdsShowForced || !isPremiumPurchased && isInTrialPeriodEnded

KVO support

Bindy supports KVO, so you can create Observable from any KVO capable property with easy subscript syntax like:

let textField = UITextField()
let text = textField[\.text] // type will be Observable<String?>

text.observe(self) { newText in
    print(newText)
}

Old value

For any Observable type you can receive old value in closure, just pass two parameters to binding closure, first one will be an old value, the second one – new value:

let observableString = Observable("test")

observableString.bind(self) { oldString, newString in
    print("String changed from \(oldString) to \(newString)")
}

High order functions

Bindy contains some high order functions:

• map - applies on any type, behavior similar to a swift map.
• flatMap - applies on Observable with optional type, returns Signal with non-optional type.
• compactMap - applies on Observable with Collection inside, behavior similar to a swift version of the function.
• reduce - applies on Observable with Collection inside, behavior similar to a swift version of the function.
• filter - applies on Observable with Collection inside, behavior similar to a swift version of the function.