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")
}

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.