Call swift init and omit parentheses because last (and only) argument is a closure

LKSwitch.swift

//: Playground - noun: a place where people can play

import UIKit

class LKSwitch : UISwitch {
    let action: (UISwitch) -> Void
    
    init(action: @escaping (UISwitch) -> Void) {
        self.action = action
        super.init(frame: .zero)
        
        self.addTarget(self, action: #selector(didPress), for: .valueChanged)
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    @objc private func didPress() {
        action(self)
    }
}

let mySwitch = LKSwitch { sender in
    print("switch is on: \(sender.isOn)")
}