Or is there some other clever way to solve this

Question

dalexander · Answer

You certainly could used a sealed class with inner classes to solve it You might also want to look at <https kotlinlang org docs reference visibility modifiers html> for what visibilities can be seen by subclasses if you aren t familiar with them

dalexander · Answer

If your base class is abstract it won t be able to be directly instantiated if you weren t already marking it abstract

Esa · Answer

Hm okay Its `private sealed class` for now as I only want to see it used in this file and in this specific way

Esa · Answer

What am I doing wrong here since I dont see the values in Product

dalexander · Answer

`Software` doesn t automatically extend from `Product` You need to explicitly do that

Esa · Answer

Ah thanks That solved it

Esa · Answer

Struggling a bit with initializing the subclass now `Constructor of inner class can be called only with receiver of containing class` Not sure I follow what this means

dalexander · Answer

Can you share the line that s not working

Esa · Answer

``` private sealed class Product val a Int inner class Software val b String Product a private fun test val c = Product Software S 1 ```

dalexander · Answer

Oh don t mark it an inner class It should just be `class software`

Esa · Answer

That turns the `a` invisible for the `Software`

dalexander · Answer

`inner class` means that it s capturing all of the properties in the containing class It s what a non static inner class does in Java if you re familiar with Java

dalexander · Answer

Yeah but if you need an `a` it should be a parameter to `Software`

dalexander · Answer

If you want to do it with the `inner class` then you need to do `Product 1 Software ` I believe

dalexander · Answer

Because that parameter has to come from somewhere after all slightly smiling face

Esa · Answer

Oh Hm So in this context a `Product` has some values that does not really care whether it is software or not I thought it would make sense to place these values on the `Product` class and not the subclass

Esa · Answer

Oh I see what you mean now

Esa · Answer

Like this right

dalexander · Answer

Yep slightly smiling face If you re going to use the `inner class` syntax then what you re actually doing it creating an instance of `Product` then creating a `Software` which extends `Product` but has a different `Product` as its outer class This way is cleaner because the only `Product` is the one that s the super class of `Software`

Esa · Answer

Lets say I did decide to go with the inner approach How would I initialize an instance of Product Software somewhere

dalexander · Answer

Well you have to have an instance of `Product` so for example ```val p = Product 1 val s = p Software a ``` similar syntax exists in Java for this case it s just rarely used

Esa · Answer

Aha okay so that means inner classes and sealed classes dont really work together as sealed classes prevent initializing the super class and inner subclasses demands it

dalexander · Answer

Hm I hadn t tried to use them together before but I think that s correct It s possible there should be a compiler error message preventing it or at least warning about it

Esa · Answer

Reason I am asking is because this becomes quite verbose as I have to list the super arguments twice

Esa · Answer

It works well for smaller classes like this example

Esa · Answer

but if the super has values `a` through `e` you have a lot of stuff to list in both the `software` constructor and the ` Product ` constructor

dalexander · Answer

Hm well another way you could look at this is making `Product` an interface and passing product as a parameter to your `Hardware` or `Software` classes creating some kind of interface for `Product` and then using class delegation ie `class Software a Int product Product ProductInterface by product` That moves the code repetition to creating `ProductInterface` rather than having more constructor parameters assuming you have so many constructor parameters you re concerned The problem is that maintaining `ProductInterface` can become tedious depending on how many methods it has and how often you add remove methods

Jérémy Touati · Answer

I have a class `Product` that I do not want to see initialized by itself but as one of its subclasses `Hardware` or `Software` The two subclasses has unique values of their own but the `Product` class has a few shared values that both hardware software products will have didn t you simply describe an abstract `Product` class with `Hardware` and `Software` concrete subclasses i must be missing something though like this <https pl kotl in 2JD Qz4WF>