Use Function in Initializer - Swift?

Question

Assume the following:

class A {
    let x : Int
    init() {
        self.x = assign(1)
    }
    func assign(y : Int) -> Int {
        return y
    }
}

This produces an error.

Here is my question : is there a way to call functions within the class initializer?

EDIT: Added error message:

use of 'self' in method call 'assign' before all stored properties are initialized

What is the exception / error you are getting? Would be helpful to see the actual result you are getting — konkked, Mar 25 '16 at 13:04
There are multiple solutions but a real use case would help. — Sulthan, Mar 25 '16 at 13:13

score 3 · Answer 1 · answered Mar 25 '16 at 13:18

You can't call instance methods until the instance is initialized (before init is done), but you can use module-level functions and type methods defined using the class or static keyword.

func compute(y: Int) -> Int {
  return y
}

class A {
  let x: Int

  static func assign(y: Int) -> Int {
    return y
  }

  init () {
    x = A.assign(3) + compute(4)
  }
}

score 3 · Answer 2 · answered Jul 17 '19 at 19:19

One other (possibly helpful) option is to have the function you call within the initializer scope:

class A {
    let x : Int
    init() {
        func assign(y : Int) -> Int {
            return y
        }
        self.x = assign(y: 1)
    }
}

I'm doing that in a project right now. I have a large initializer (its actually a parser) and use an initializer-scoped function for error reporting. Of course, I'd prefer the function to be at class scope so I can reuse it between initializers. But at least I can reuse it within each initializer.

score 2 · Accepted Answer · answered Mar 25 '16 at 13:10

2

I think it is not the greatest solution but still it is working.

 class A {
        var variable : Int

        init() {

            self.variable = A.assign(1)

        }

        private class func assign(y : Int) -> Int {
            return y
        }
    }

answered Mar 25 '16 at 13:10

Oleg Gordiichuk

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It works, thanks. Out of curiosity, why does this work while the previous method did not? – Brandon Bradley Mar 25 '16 at 13:16
it is a class function and this kind of function do not need initialization of the object or @Sulthan could you deeply explain – Oleg Gordiichuk Mar 25 '16 at 13:19
I have a huge function that I would like to call from several init() methods. This huge function initializes several of the class properties. I have done as above, making this huge method a 'class' function, but I get an error on every property in the method. Of course, if I copy and paste this code into each init() method, it works. – Brian Reinhold Oct 02 '20 at 11:24

score 0 · Answer 4 · edited May 23 '17 at 12:16

0

You could use somethings like:

class A {
    var x : Int!
    init() {
        x = assign(1)
    }
    func assign(y : Int) -> Int {
        return y
    }
}

The downside of this approach is that you will get a runtime error if you access x and it is not initialised. Check out this answer.

edited May 23 '17 at 12:16

Community

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answered Mar 25 '16 at 13:11

Jelly

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It works because now `x` is optional so the error doesn't apply anymore. Now you do not use `self` before all stored properties are initialised because you do not have such properties anymore, now they are optionals. – Jelly Mar 25 '16 at 14:00

Use Function in Initializer - Swift?

4 Answers4