Array of first-class functions as an instance variable in Swift

Question

I experience the following problem trying to create a variable that stores an array of functions:

class MySwiftClass {

    // Compilation Error: '()' is not a subtype of 'MySwiftClass'
    var arrayOfFunctions: [() -> Int] = [myFunction] 

    func myFunction() -> Int {
        return 0
    }
}

Actually this code cannot be compiled with error:

'()' is not a subtype of 'MySwiftClass'

But it works if setup this array in runtime:

class MySwiftClass {
    var arrayOfFunctions: [() -> Int] = [() -> Int]()

    init() {
         arrayOfFunctions = [myFunction]
    }

    func myFunction() -> Int {
        return 0
    }
}

Can anybody explain whether it's a bug of Swift compiler or it's expected behaviour? I don't see any reason for compilation error in the first case, moreover error description is meaningfulness as for me.

tng · Accepted Answer · 2015-03-19 20:08:34Z

3

It's by design in Swift. A initializer assigned to a property (in your case, arrayOfFunctions) cannot access self before init is run. In your case, it's trying to access self.myFunction. You can only access self safely in the init method.

Look here https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html at "Safety Check 4".

answered Mar 19, 2015 at 20:08

tng

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Comments

William Kinaan · Accepted Answer · 2015-09-11 22:44:10Z

0

As @tng stated, that is correct, and I would like to propose a solution, which is using a static method, like this:

class MySwiftClass {


    var arrayOfFunctions: [() -> Int] = [MySwiftClass.myFunction]

    static func myFunction() -> Int {
        return 0
    }
}

answered Sep 11, 2015 at 22:44

William Kinaan

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