Given a data class like this: ```data class State ( val aField : String val bField : String val ...

# getting-started

[Daniele B]

Given a data class like this:

data class State (
	val aField : String
	val bField : String
	val cField : String
)

I would like to wrap this copy function:

wrapperobject.state = wrapperobject.state.copy (aField = aValue, bField = bValue)

inside a custom method like this:

wrapperobject.changeState(aField = aValue, bField = bValue)

what would be the code for it?

I am not sure how to define the argument of the changeState method

[Shawn]

I feel like I’m misunderstanding your question but can’t you just implement it like this?

class WrapperObject(var state: State)
  fun changeState(aField: String, bField: String) {
    state = state.copy(aField = aField, bField = bField)
  }
}

[Daniele B]

is there anyway to extract the arguments directly from the State class definition, without having to specify them?

[Daniele B]

as the arguments could be many, in this way I would have to replicate them in both the class definition and the changeState method

[Shawn]

do you care about restricting the modification of specific fields in the State object?

[Shawn]

(I saw there was a cField you didn’t include in the later examples, wasn’t sure if that was intentional)

[Daniele B]

hopefully yes, but I was wondering if Kotlin offered some easy way of matching the arguments of a method to the the properties of a class

[Daniele B]

I guess copy is a very special function

[Daniele B]

I wanted to mimic the same behaviour

[Daniele B]

with the chance also of not specifying all the properties

[Shawn]

unfortunately yes, copy on data classes is a unique case

[Daniele B]

ok, I see

[Daniele B]

thanks