UIView<SomeProtocol> in Swift

droppable_uiview.swift

import UIKit

protocol Droppable {
  func dropped()
}

class A: UIView, Droppable {
  func dropped() {
    print("A")
  }
}

class B: UIView, Droppable {
  func dropped() {
    print("B")
  }
}

let a = A()
let b = B()

let aDropped: Droppable = a
aDropped.dropped()

let aView: UIView = a
aView.frame

/// T reflects: “I need a thing that conforms to the Droppable protocol and which is some kind of UIView.”
class Test<T: UIView where T: Droppable> {
  let property: T

  init(property: T) {
    self.property = property
  }

  func printGenericConstraint<P: UIView where P: Droppable>(parameter: P) {
    print(parameter)
  }

  func printProtocol(parameter: Droppable) {
    print(parameter)
  }

  func printDroppables(droppables: [Droppable]) {
    print(droppables)
  }

  func printViews(views: [UIView]) {
    print(views)
  }
}

let test: Test = Test(property: a)
test.property.frame
test.property.dropped()
test.printGenericConstraint(b)
test.printProtocol(b)
test.printGenericConstraint(a)
test.printProtocol(a)
test.printDroppables([a, b])
test.printViews([a, b])