so, let me see if I got constructors straight... 1...

# announcements

[Dalinar]

so, let me see if I got constructors straight...
1. if you have a single constructor then () after the classname is not required...
2. however if you have secondary constructors then it is now required
3. and now you might also want to make that constructor private

[gildor]

no, it’s incorrect

[gildor]

contructor keyword is optional for primary constructor and requires for secondary

[hho]

https://kotlinlang.org/docs/reference/classes.html#secondary-constructors

[gildor]

also one case when you need constructor keyword for primary, if you want add annotation to primary constructor or add visibility modifier (what you also mentioned in 3)

[Dalinar]

ok wait

[Dalinar]

what I mean is if I removed () from after the classname, and then have secondary constructors then IDE will give me the error supertype initialization is imposssible without a primary constrctor.. so in this case the () is required

[Dalinar]

but then I should make it a private constructor to avoid being able to call a no-args constructor?

[Dalinar]

my thinking is correct?

[diesieben07]

To create a new instance you always need to use ClassName()

[diesieben07]

The () are never optional.

[diesieben07]

ClassName refers to the companion object of the class.

[Dalinar]

no, () in the class declaration i mean - not invoking it - class Abc: Def() vs class Abc(): Def()

[Alowaniak]

it doesn't make a lot of sense to have a secondary constructor but effectively no primary constructor though

[diesieben07]

Yes, the shorthand for calling super (Def() in your first example) only works with primary constructor.

[diesieben07]

It does not make any sense otherwise (which constructor should the super call refer to?)

[Shawn]

class Abc() isn’t invoking a constructor, it’s a redundant set of parens since your constructor is noarg

[Dalinar]

sure it makes sense, I want to prevent incorrect object creation via noargs constructor in my class

[Dalinar]

otherwise my lateinit fields won't be initalized properly since that code is in the secondary constructors

[diesieben07]

class Abc() : Def() is short for:

class Abc : Def {
    constructor() : super() {
    }
}

[diesieben07]

If you don't specify the primary constructor, Kotlin won't magically add one. So:

class Abc : Def {
    // secondary constructors here
}

In that example Abc is guaranteed to have one of it's secondary constructors called (since there is no primary one)

[Dalinar]

thanks for the help

[hho]

https://pl.kotl.in/BJM5LnHX4

[Dico]

You are correct that omitting () in your class declaration and including a constructor in the body removes the implicit no-arg constructor that would otherwise be present .