Swift protocol property set not executed - swift

Question

I try to use the set method for calling a function after the value is changed.
I did not see why the set method is not called.
The code could be directly executed in playground
//: Playground - noun: a place where people can play
import UIKit
protocol RandomItem {
var range : (Int,Int) {get set}
var result : Int {get set}
init()
mutating func createRandom()
}
extension RandomItem {
var range : (Int,Int) {
get {
return range
}
set {
range = newValue
self.createRandom()
}
}
}
struct Item: RandomItem {
var range = (0,1)
var result: Int = 0
init() {
self.createRandom()
}
mutating func createRandom() {
let low = UInt32(range.0)
let high = UInt32(range.1)
result = Int(arc4random_uniform(high - low + 1) + low)
}
}

Answer 1

Your struct Item declares its own range property, which overrides the default you created in the protocol extension. The range property in Item has no getters or setters defined to do what your extension version does.
Another issue:
Your protocol extension defines the range property as a computed property (no storage) whose getter and setter both call itself. This will loop infinitely.
Maybe you are looking for something more like:
protocol RandomItem {
var storedRange: (Int, Int) { get }
var range : (Int,Int) {get set}
var result : Int {get set}
init()
mutating func createRandom()
}
extension RandomItem {
var range : (Int,Int) {
get {
return storedRange
}
set {
storedRange = newValue
self.createRandom()
}
}
}
struct Item: RandomItem {
var result: Int = 0
var storedRange = (0, 1)
init() {
self.createRandom()
}
mutating func createRandom() {
let low = UInt32(range.0)
let high = UInt32(range.1)
result = Int(arc4random_uniform(high - low + 1) + low)
}
}
This requires a conforming type to define a stored property storedRange, which the default implementation of the computed property range will interact with.