apply.swift

import UIKit

/* attempt 1 */

protocol HasApply { }

extension HasApply {
    
    func apply(_ applying: (Self) -> Void) -> Self {
        applying(self)
        
        return self
    }
    
}

extension NSObject: HasApply { }

let imageView = UIImageView().apply {
    $0.contentMode = .scaleAspectFill
    $0.layer.cornerRadius = 4
}

assert(imageView.contentMode == .scaleAspectFill)
assert(imageView.layer.cornerRadius == 4)

/* attempt 2 */

typealias ApplyFunction<T> = (T) -> Void

protocol HasApply2 { }

extension HasApply2 {
    
    func apply2(_ applyFunctions: ApplyFunction<Self>...) -> Self {
        for applyFunction in applyFunctions {
            applyFunction(self)
        }
        
        return self
    }
    
}

extension NSObject: HasApply2 { }

func setContentMode(_ contentMode: UIViewContentMode) -> ApplyFunction<UIImageView> {
    return {
        $0.contentMode = contentMode
    }
}

func setCornerRadius(_ cornerRadius: CGFloat) -> ApplyFunction<UIImageView> {
    return {
        $0.layer.cornerRadius = cornerRadius
    }
}

let imageView2 = UIImageView().apply2 (
    setContentMode(.scaleAspectFill),
    setCornerRadius(4)
)

assert(imageView2.contentMode == .scaleAspectFill)
assert(imageView2.layer.cornerRadius == 4)


/* attempt 3 */

infix operator &&&

extension HasApply2 {
    
    func apply2(_ applyFunctions: [ApplyFunction<Self>]) -> Self {
        for applyFunction in applyFunctions {
            applyFunction(self)
        }
        
        return self
    }
    
}

func &&&<T: HasApply2>(lhs: T, rhs: [ApplyFunction<T>]) -> T {
    return lhs.apply2(rhs) // this does not compile?!
}

let imageView3 = UIImageView() &&& [
    setContentMode(.scaleAspectFill),
    setCornerRadius(4)
]

assert(imageView3.contentMode == .scaleAspectFill)
assert(imageView3.layer.cornerRadius == 4)

/* attempt 4 */

precedencegroup ForwardApply {
    associativity: left
    higherThan: LogicalConjunctionPrecedence
}

infix operator &> : ForwardApply

func &> <T>(lhs: T, rhs: (T) -> Void) -> T {
    rhs(lhs)
    
    return lhs
}

let imageView4 = UIImageView()
    &> setContentMode(.scaleAspectFill)
    &> setCornerRadius(4)

assert(imageView4.contentMode == .scaleAspectFill)
assert(imageView4.layer.cornerRadius == 4)

tl ; dr

let imageView = UIImageView().apply {
    $0.contentMode = .scaleAspectFill
    $0.layer.cornerRadius = 4
}

let imageView2 = UIImageView().apply2 (
    setContentMode(.scaleAspectFill),
    setCornerRadius(4)
)

let imageView3 = UIImageView() &&& [
    setContentMode(.scaleAspectFill),
    setCornerRadius(4)
]

let imageView4 = UIImageView()
    &> setContentMode(.scaleAspectFill)
    &> setCornerRadius(4)