🤘🏼 🏗️ 🤙🏽 Understanding Opaque Return Types in Swift 🖤 🌋 😄

Hi, Habr. As part of the course “iOS Developer. Professional ” prepared a translation of useful material for you.

We also invite you to take part in an open webinar on the topic "Writing an application in SwiftUI and Combine" . Participants, together with an expert, will understand what SwiftUI and the Combine framework are, as well as how to create a small application with their help.

You can also read this article on my Xcoding With Alfian blog by following the link .

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)/ (method

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), , API. , (protocol

). API- , opaque type

some. Swift (identity

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View, some

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.

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Opaque return types

opaque return type , , .

associatedtype

, MobileOS. associatedtype

( ) Version , Version, , .

protocol MobileOS {
    associatedtype Version
    var version: Version { get }
    init(version: Version)
}

: iOS Android. . IOS float, Android String ( Android 10).

struct iOS: MobileOS {
    var version: Float
}
struct Android: MobileOS {
    var version: String
}

, , MobileOS . , :

1 ( ):

func buildPreferredOS() -> MobileOS {
    return iOS(version: 13.1)
}
//  
 'MobileOS'      , 
        Self  associated type.

, , , associatedtype

. . , .

2 ( ):

func buildPreferredOS() -> iOS {
    return iOS(version: 13.1)
}
//

, , , API . , Android .

3 (Generic Function Return)

func buildPreferredOS<T: MobileOS>(version: T.Version) -> T {
    return T(version: version)
}
let android: Android =  buildPreferredOS(version: "Jelly Bean")
let ios: iOS = buildPreferredOS(version: 5.0)

, . , API, . , , .

( Opaque Return Type)

func buildPreferredOS() -> some MobileOS {
    return iOS(version: 13.1)
}

opaque return type

, , , MobileOS . , , MobileOS.

Opaque returns types

, , , opaque return type

, .

func buildPreferredOS() -> some MobileOS {
   let isEven = Int.random(in: 0...100) % 2 == 0
   return isEven ? iOS(version: 13.1) : Android(version: "Pie")
}
//  
     'iOS' 
    'some MobileOS'

func buildPreferredOS() -> some MobileOS {
   let isEven = Int.random(in: 0...100) % 2 == 0
   return isEven ? iOS(version: 13.1) : iOS(version: "13.0")
}
//

, opaque return value

. .

opaque return type API

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API , for

(print) .

1. Generic Return Function

func sliceFirstAndEndSquareProtocol<T: Numeric>(array: Array<T>) -> LazyMapSequence<ArraySlice<T>, T> {
   return array.dropFirst().dropLast().lazy.map { $0 * $0 }
}
sliceFirstAndEndSquareProtocol(array: [2,3,4,5]).forEach { print($0) }
// 9
// 16

, LazyMapSequence, T>

, .

2. Opaque Return Types

func sliceHeadTailSquareOpaque<T: Numeric>(array: Array<T>) -> some Sequence {
    return array.dropFirst().dropLast().lazy.map { $0 * $0 }
}
sliceHeadTailSquareOpaque(array: [3,6,9]).forEach { print($0) }
// 36

, , sequence, .

Opaque Return Types SwiftUI

SwiftUI , body View , View. .

struct Row: View {
    var body: some View {
        HStack {
           Text("Hello SwiftUI")
           Image(systemName: "star.fill")
        }
    }
}

body

:

HStack<TupleView<(Text, Image)>>

, , , view

HStack. Opaque return type

SwiftUI. API View, View.

Opaque return type

opaque return type

, , . , Apple.

apple/swift-evolution

, …

github.com

Opaque Types — Swift (Swift 5.1)

opaque return type . …

docs.swift.org

Swift - WWDC 2019 - - Apple Developer

Swift Apple, …

developer.apple.com

, Swift, Swift WWDC 2014. , , API, , associatedtype

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, Apple Swift , , Swift Evolution. , Swift Language ( struct Swift 5.1 ).

Swift . , - . , , , . !

«iOS Developer. Professional».

« SwiftUI Combine».

Understanding Opaque Return Types in Swift