Initialisation

Cocoa Programming for OS X (5th Edition) 3. Structures and Classes
1

In the initial discussion I don’t understand why there need to be two initialisers. It isn’t clear from the text to me, all I see is a reference to “initialisers”. Why is there one init() with n parameters and that defines two parameters and assigns an x to itself as an x?

2

Hello
I think the the problem is :
Struct offers:

  • a default initializer for their properties if all of them have a default value (for optional they receive the default nil) and there is not another custom initializer:
struct Pippo {
   var x:Int = 3
   var y:Int = 4
}
let pippo = Pippo() //init x with 3, the default
  • a memberwise initializer if there aren’t custom initializers or default initializer due the fact that a property has not a default value
struct Pippo {
    var x:Int = 3
    let y:Int 
}
let pipe = Pippo(x:3, y: 4)   //the memberwise
  • if there is a custom initializer the default and memberwise disappear, you don’t need them
struct Pippo {
    var x:Int
    let y:Int = 4
    init(customX x:Int){   //customX is a alias for x 
        self.x = x // you need self because here the x is local and obscures the property of struct with same name
    }
}
let pippo = Pippo(customX: 3) //this use the custom

So if you want a default-like initializer and a memberwise-like you have to write both of them