kotlin using data class generics type

Question

Hi there I have gone thru the kotlin documentation and haven't found anything. What I want to do is have a generic thar must be a data class, something like

data class MyData(val pop1:Long,val pop2:String,...)

fun class MyGenericClass<T : isDataClass>(o : T){
    // This is the important part
    fun useCopy(value : Long) = t.copy(pop1 = value)
}

What I really need to achieve is to be able to use the copy function of data classes in a generic way(pop1 will always be a member of my data classes)

Thanks in advance

And what if the class doesn't have a pop1 member? My suggestion would be to define an interface, and then have your (data) classes inherit from that. — Oliver Charlesworth
– Oliver Charlesworth, Commented Nov 12, 2017 at 19:00
thats how I have it now, but the problem is the copy method having a method copy(pop1:Long) in the interface does not use the data class one — Ricardo Garza V.
– Ricardo Garza V., Commented Nov 12, 2017 at 19:23
You could just have a sealed class or an interface and then use reflection with named arguments, although it probably would make sense to rethink your problem. This is an unusual use case. — Salem
– Salem, Commented Nov 12, 2017 at 19:29

s1m0nw1 · Accepted Answer · 2018-02-10 21:41:07Z

3

You should consider using an interface for that particular problem. Just delegate to the data class copy in the implementation.

data class MyData(val pop1: Long, val pop2: String) : Pop1Data {
    override fun copy(pop1: Long) {
        copy(pop1 = pop)
    }
}

interface Pop1Data {
    fun copy(pop1: Long)
}

class MyGenericClass<T : Pop1Data>(private val o: T) {
    // This is the important part
    fun useCopy(value: Long) = o.copy(value)
}

edited Feb 10, 2018 at 21:41

answered Nov 12, 2017 at 19:53

s1m0nw1

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2 Comments

Dina Bogdan Over a year ago

And how about the scenario when I have multiple and variant properties of some data classes? Is there a way to handle this scenario?

Joe Dow Over a year ago

I haven't check this solution yet for my scenario, but I think it would be possible to pass into generic copy() method a whole interface instead of just property and due inheritance convert the actual argument to the specific type, e.g. override fun copy(obj: PopData) { copy(param1 = (obj as Pop1Data).pop1, isCompleted = (obj as Pop1Data).pop2) }

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