[swift-evolution] [Idea] Set variables to "_" in two-stage init; remove IUO

[Vladimir.S]

The question is if we can solve the problem with special private init() and 
convenience inits ?

class MyBase {
     init () {

     }
}

class MyClass : MyBase {

     let x:Int
     let y:String
     let z:Double

     private init(_ xValue: Int, _ zValue: Double) {
         self.x = xValue
         self.y = "\(xValue) - \(zValue)"
         self.z = zValue

         super.init()
     }

    convenience override init() {
         self.init(1, 1.0)
    }

    convenience init(x: Int) {
         self.init(x, 1.0)
    }

    convenience init(z: Double) {
         self.init(1, z)
    }
}

print(MyClass().y)
print(MyClass(x: 10).y)
print(MyClass(z: 10.0).y)

Seems like we can. Any drawbacks?

On 16.06.2016 9:27, Jonathan Hull via swift-evolution wrote:
> I don’t remember a proposal for that, but I would definitely support one.
>  I use this pattern all the time (usually by initializing to a default
> value first), and it would be nice to have an explicit/safe way to handle
> it, (and to avoid waisting cycles creating an object I never use).
>
> Perhaps we should spell it @init or @initHelp:
>
> class MyClass : MySuperClass {
>
>     let x:Int
>     let y:String
>     let z:Double
>
>     @init func commonSetup() {
>         self.y = “My String”
>         self.z = 4.2
>     }
>
>    init(x: Int) {
>         self.x = x
>         commonSetup() //No error because commonSetup() sets the value of
> ‘y’ & ‘z'
>         super.init()
>    }
> }
>
> Basically the @init functions would be inlined into the init.  They would
> only be callable from inits, and could only be called a single time within
> each init.
>
> Thanks,
> Jon
>
>> I believe there was(was?) already a suggestion to introduce special methods
>> that could be called from initializers. IMO this is a better solution to
>> the problem as you really should not call 'usual' instance method until the
>> instance is fully instantiated(super.init() called in your case):
>>
>> class MyClass : MySuperClass {
>>
>> 	let x : Int
>> 	let y : String  //let!
>>
>> 	initfunc calcY(somePatam: Int) -> String {
>> 		return ....
>> 	}
>>
>> 	init(x: Int) {
>> 		self.x = x
>> 		self.y = assignY(5)
>> 		super.init()
>> 	}
>> }
>
>
>
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