Hello everyone, how can I create a data structure ...

# announcements

[stefano.maffullo]

Hello everyone, how can I create a data structure for example with two different types like ArrayList<Double, String>

[jamie-purchase]

this is likely a naive solution but in Java you could say ArrayList<Object> and cast them in and out... or create a class that has a property of either Double or String and have an ArrayList<MyClass> but as for Kotlin likely far better ways

[jamie-purchase]

to clarify: one value per element of type Double or String right?
if it's a double and string per element then use ArrayList<Pair...

[karelpeeters]

You can also take a look at Either from either #C0B8E36SG or #C5UPMM0A0.

[cedric]

@stefano.maffullo Short answer is you can't in Kotlin, but a language like Ceylon can. In Kotlin, you'd create your own structure that contains all the types you need and discriminate on them (e.g. Either)

[stefano.maffullo]

Yeah it's fine for me to create my own structure, so my own "structure" it's a Class/Object?

[cedric]

For example data class MyStructure { val d: Double, val s: String } and put that in your list

[cedric]

Might want to make it a bit more sophisticated so you don't need to type check to know which field is present/absent

[stefano.maffullo]

Thank you very much! Can I bother with another question? Is better a list of MyStructure or a 2D array?

[cedric]

As a general rule, avoid using arrays. So ArrayList.

[cedric]

e.g. listOf() or mutableListOf()

[stefano.maffullo]

So I'll use listOf<MyClass>

[jamie-purchase]

@cedric can I ask why you would suggest avoiding arrays?

[cedric]

The general reason is that arrays don't play nicely with generics, mostly because they predate them. This was already a rule of thumb in Java so it's not specific to Kotlin