A question related to reflection and `data class`’s copy method. Currently I am have something like ...

# announcements

[edwardwongtl]

A question related to reflection and `data class`’s copy method.
Currently I am have something like this

enum class GeneralModifier {
    Less, Normal
}

data class Latte(
    val ice: GeneralModifier = GeneralModifier.Normal,
    val milk: GeneralModifier = GeneralModifier.Normal
) : Coffee()

And the selection input is Pair<String, Enum<GeneralModifier>>, where the first one is the field name, e.g. “ice”
So I do

tem.copy(
  ice = if (field == "ice") GeneralModifier.values().first { it == option } else item.ice,
  milk = if (field == "milk") GeneralModifier.values().first { it == option } else item.milk
)

Is there a easier way to do the copy?

[Joris PZ]

I would do something like

data class Latte(
    val ice: GeneralModifier = GeneralModifier.Normal,
    val milk: GeneralModifier = GeneralModifier.Normal
) : Coffee() {
    
    fun modify(input: Pair<String, GeneralModifier>) =
        when(input.first) {
            "ice" -> this.copy(ice = input.second)
            "milk" -> this.copy(milk = input.second)
            else -> this
        }
}

[edwardwongtl]

Then I have to repeat the function for every similar class..seems not much better

[Joris PZ]

Maybe something like this is what you are looking for?

data class Person(val name: String, val age: Int)
    val person = Person("Jane", 23)
    val copy = person::class.memberFunctions.first { it.name == "copy" }
    val instanceParam = copy.instanceParameter!!
    val ageParam = copy.parameters.first { it.name == "age" }
    val result = copy.callBy(mapOf(instanceParam to person, ageParam to 18))
    println(result)

Taken from https://stackoverflow.com/questions/49511098/call-data-class-copy-via-reflection

[Joris PZ]

Wouldn't be too hard to adapt this to your case

[edwardwongtl]

This seems to be a more general solution, I’ll give it a try

[edwardwongtl]

The copy via reflection works like a charm! Thanks a lot