Learning Kotlin and Swift

Explore Kotlin and Swift together and learn their differences

Elye

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Oct 18, 2020 · 3 min read

In Mobile development, the 2 major programming language to learn is Swift and Kotlin. They look very similar, but there are subtle differences.

Let’s look at the one called during construction, the init that exist in both Kotlin and Swift.

The init function

In Swift, init is the constructor and is called before the parent is constructed.

In Kotlin, the init is not really a constructor, and it is called after the parent is constructored.

More details below.

In Swift

1. The init function can have parameters to form a constructor for the class.
2. Cannot have more than one init() function in the class (i.e. empty parameter constructor)
3. The init function is called before the parent constructor is called i.e. the parent object is not yet formed.
4. The init function cannot call the class member function unless it’s a static function. The reason is because the parent is not constructed yet, so the child object is not constructed yet.

class Base {
    private let someString: String
    init(someString: String) {
        print("In Base init")
        self.someString = someString
    }
}class Child: Base {
    init() {
        print("In Child init")
        super.init(someString: ChildClass.localStaticFunction())
    }static func localStaticFunction() -> String {
        print("In local static function")
        return "something"
    }
}

The result of the above code will be

In Child class init
In local static function
In Base init

In Kotlin

1. The init scope cannot have parameters to form a constructor for the class. The constructor is the actual constructor function that can have parameter.
2. Can have more than one init scope in the class. The execution order dependent of the order where it is placed
3. The init scope is called after the parent constructor is called i.e. the parent object is already formed. (note, the constructor function is also called after the parent is constructed)
4. The init scope can call the class member function .The reason is because the object has been constructed.

open class Base {
    private val something: String
    constructor(something: String) {
        this.something = something
        println("In Base constructor")
    }
    init {
        println("In Parent Init")
    }Base}class Child: Base {
    constructor(something: String): super(something) {
        println("In Child Constructor")
    }
    init {
        println("In Child Init")
        localFunction()
    }
    private fun localFunction() {
        println("In Local Function")
    }
}

The result of the above code will be

In Base Init
In Base constructor
In Child Init
In Local Function
In Child Constructor

Summary

To summarize, I have put them side by. side for easier comparison.

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