``` data class Foo private constructor val a Int val b Int f kotlinlang #announcements

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Title

Andreas Sinz

03/10/2018, 4:32 PM

data class Foo private constructor (val a: Int, val b: Int)

fun Foo(a: Int, b: Int) = ...

Shawn

03/10/2018, 4:40 PM

it looks like that results in a conflicting override (and an accidental recursive call)

and if I change the method name, I still can’t access the private constructor from a top-level function

Andreas Sinz

03/10/2018, 4:41 PM

function and data class must be in the same file

Shawn

03/10/2018, 4:43 PM

they’re declared literally one after another in my code

Andreas Sinz

03/10/2018, 4:49 PM

nvm ^^

I get a runtime exception

so the best way is to use a

companion object

with

operator fun invoke

➕ 1

that should work with a private constructor

Shawn

03/10/2018, 4:59 PM

oh wow, that works pretty well 👍

Andreas Sinz

03/10/2018, 5:00 PM

yes, just make sure you override

copy

serg

03/10/2018, 5:32 PM

How do you "override" a generated function?

Shawn

03/10/2018, 5:33 PM

I’m not sure that you can - I got a platform declaration clash when I tried

Andreas Sinz

03/10/2018, 6:10 PM

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

If there are explicit implementations of equals(), hashCode() or toString() in the data class body or final implementations in a superclass, then these functions are not generated, and the existing implementations are used

and

Deriving a data class from a type that already has a copy(...) function with a matching signature is deprecated in Kotlin 1.2 and will be prohibited in Kotlin 1.3.

so you can't override

copy()

componentN()

😕

Shawn

03/10/2018, 6:12 PM

so it goes 😕

Andreas Sinz

03/10/2018, 6:13 PM

TIL wasn't aware that you can't override all methods that are generated

serg

03/11/2018, 12:15 PM

In this case it would help just to prohibit (make private) the

copy()

method. I think it would make sense to give a finer grain control over generated methods.

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