A port of Kotlin's scope functions to Swift.

ScopeFuncs.swift

protocol ScopeFunc {}
extension ScopeFunc {
    @inline(__always) func apply(block: (Self) -> ()) -> Self {
        block(self)
        return self
    }
    @inline(__always) func letIt<R>(block: (Self) -> R) -> R {
        return block(self)
    }
}
extension NSObject: ScopeFunc {}

usage.swift

let imageView = UIImageView().apply {
    $0.contentMode = .ScaleAspectFit
    $0.opaque = true
    $0.frame = CGRectMake(...)
    $0.setImageWithURL(NSURL(string: "..."))
}

CAKeyframeAnimation(keyPath: "transform.rotation").apply {
    $0.beginTime = CACurrentMediaTime()+delay
    $0.duration = 0.2
    $0.repeatCount = 10
    $0.values = [ 0.005*M_PI, -0.005*M_PI, 0.005*M_PI ]
    
    imageView.layer.addAnimation($0, forKey: "wiggle")
}

Nice extensions!! I love apply in Kotlin and wanted to use it in Swift as well!

But there seem to be an issue with Autocomplete in the closure (I'm using XCode 10.2.1)

It only shows the useless _ self property:

The funny thing is that once the property and its assignment are fully typed, Xcode highlights them, meaning it recognizes them as valid:

Does anyone have a fix to make autocomplete work in this case?

Kotlin scope functions also play nicely with optionals, you can also add the scope function for Optionals in swift like:

extension Optional where Wrapped: ScopeFunc {
    @inline(__always) func `let`<R>(block: (Wrapped) -> R) -> R? {
        guard let self = self else { return nil }
        return block(self)
    }
}

extension String: ScopeFunc {}

Which means you can do:

        let optionalNumberString: String? = "5"
        let optionalNumber: Int? = optionalNumberString?.let{ Int($0) }

@langleyd

note:

// https://developer.apple.com/documentation/swift/int/2927504-init
// -------------------------------------------------------------------
struct Int {
      init?(_ description: String)
 }

So

let optionalNumberString: String? = "5"
let optionalNumber: Int? = optionalNumberString?.let{    Int($0)     }

equals

let optionalNumberString: String? = "5"
let optionalNumber: Int?? = optionalNumberString.let{     Int($0)     }

equals

let optionalNumberString: String? = "5"
let optionalNumber: Int? = optionalNumberString.let{     Int($0)!    }

@Guang1234567 the use of the Int constructor is just for the purpose of illustration, the point is that let can useful with optional chaining.