Parent.swift

/**
  Problem
*/
class Parent {
    
    var children:Array<String>
    
    init() {

        self.children = discoverChildren() // <-- error: method call 'discoverChildren' before all store properties are initialized
    }
    
    func discoverChildren() -> Array<String> {
        return ["a","b","c","d","e"]
    }
}

/**
  Solution #1
*/
class Parent1 {
    
    var children:Array<String>
    
    init() {

        // shut up the compiler with dummy value
        self.children = Array<String>()
        // now can call the method to provide real value
        self.children = discoverChildren()
    }
    
    func discoverChildren() -> Array<String> {
        return ["a","b","c","d","e"]
    }
}

/**
  Solution #2
*/
class Parent2 {
    
    // 'lazy' allows self reference
    lazy var children:Array<String> = {
            return self.discoverChildren()
    }()
    
    init() {
    }
    
    func discoverChildren() -> Array<String> {
        return ["a","b","c","d","e"]
    }
}