ios - Calling instance method during initialization in Swift

Question

I am new to Swift and would like to initialize an object's member variable using an instance method like this:

class MyClass {
  var x: String
  var y: String

  func createY() -> String {
    self.y = self.x + "_test" // this computation could be much more complex
  }

  init(x: String) {
    self.x = x
    self.y = self.createY()
  }     
}

Basically, instead of inlining all the initialization code in init method, I want to extract the initialization code of y to a dedicated method createY and call this instance method createY in init. However, Swift compiler (Swift 1.2 compiler in Xcode 6.3 beta) complains:

use of 'self' in method call 'xxx' before super.init initialize self

Here 'xxx' is the name of the instance method (createY).

I can understand what Swift compiler is complaining and the potential problem it wants to address. However, I have no idea how to fix it. What should be the correct way in Swift to call other instance method of initialization code in init?

Currently, I use the following trick as work around but I don't think this is the idiomatic solution to this problem (and this workaround requires y to be declared using var instead of let which makes me feel uneasy too):

init(x: String) {
  self.x = x
  super.init()
  self.y = createY()
} 

Any comment is appreciated. Thanks.

Answer 1

Convert createY() to a global or class function that accepts x as an argument and returns a y.

func createY(x: String) -> String {
    return x + "_test" // this computation could be much more complex
}

Then just call it normally from your init.

class MyClass {
  let x: String
  let y: String

  init(x: String) {
    self.x = x
    self.y = createY(x)
  }     
}