LayoutWithKeyPath.swift

import UIKit
import PlaygroundSupport


protocol With {}

extension With where Self: AnyObject {
    @discardableResult
    func configure<T>(_ property: ReferenceWritableKeyPath<Self,T>, setTo value: T) -> Self {
        self[keyPath: property] = value
        return self
    }
}

protocol Anchor: UIView {
    
}

extension Anchor {

    func anchor<T>(referentTo referent: UIView, _ from: KeyPath<UIView,T>, equal to: KeyPath<UIView,T>, constant: CGFloat = 0, multipler: CGFloat = 0) -> Self where T: NSLayoutDimension {
        self.translatesAutoresizingMaskIntoConstraints = false
        self[keyPath: from].constraint(greaterThanOrEqualTo: referent[keyPath: to], multiplier: multipler, constant: constant).isActive = true
        return self
    }
    
    func anchor<T,Axis>(referentTo referent: UIView, _ from: KeyPath<UIView,T>, equal to: KeyPath<UIView,T>, constant: CGFloat = 0, multipler: CGFloat = 0) -> Self where T: NSLayoutAnchor<Axis> {
            self.translatesAutoresizingMaskIntoConstraints = false
            self[keyPath: from].constraint(equalTo: referent[keyPath: to], constant: constant).isActive = true
            return self
        }
}



extension UIView: With, Anchor {}

let view = UIView()
    .configure(\.backgroundColor, setTo: .red)
    .configure(\.frame, setTo: CGRect(x: 0, y: 0, width: 200, height: 200))

let label = UILabel()
    .configure(\UILabel.backgroundColor, setTo: .black)
    .configure(\.baselineAdjustment, setTo: .alignCenters)
    .configure(\.text, setTo: "Hello World")
    .configure(\.textColor, setTo: .white)


view.addSubview(label)

label
    .anchor(referentTo: view, \.centerYAnchor, equal: \.centerYAnchor)
    .anchor(referentTo: view, \.centerXAnchor, equal: \.centerXAnchor)
    .anchor(referentTo: view, \.heightAnchor, equal: \.heightAnchor, multipler: 0.5)
    .anchor(referentTo: view, \.widthAnchor, equal: \.widthAnchor, multipler: 0.5)
    

PlaygroundPage.current.liveView = view