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#getting-started
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# getting-started
k
kqr
04/03/2021, 12:26 PMhello, please is there any way to "fix" this https://pl.kotl.in/oDHhNFTic ?
y
Youssef Shoaib [MOD]
04/03/2021, 12:33 PMBest I could come up with (playground):
Copy code
fun main() {
Command1Handler().execute(Command1())
Command1Handler().execute(Command2())
val commandA: Command = Command1()
val commandB: Command = Command2()
Command1Handler().execute(commandA)
Command1Handler().execute(commandB)
}
interface Command
interface CommandHandler<T> where T : Command {
fun execute(command: T)
}
class Command1 : Command
class Command2 : Command
class Command1Handler: CommandHandler<Command> {
override fun execute(command: Command) {
println("used supertype command")
when(command) {
is Command1 -> execute(command)
is Command2 -> execute(command)
else -> throw IllegalArgumentException()
}
}
fun execute(command: Command1) = println("Executing ${command.javaClass.simpleName}")
fun execute(command: Command2) = println("Executing ${command.javaClass.simpleName}")
}🙇♂️ 1
k
kqr
04/03/2021, 1:10 PMme too 😞
a
Alexis Manin
04/03/2021, 2:09 PMIs that the [expression problem](https://en.m.wikipedia.org/wiki/Expression_problem) ?
I do not think that Kotlin has direct solutions for this. Maybe in th future, an evolution on extension functions could reduce th pain. I think groovy uses "multiple dispatch" ro solve this, but that's not type safe if I understand correctly.
Maybe Sealed interfaces could help here (at the cost of extensibility) ?
https://jorgecastillo.dev/sealed-interfaces-kotlin
t
Tomasz Krakowiak
04/03/2021, 2:34 PM@kqr Your example is too generic and doesn't tell us what is the root of your problem. Why do you need to support 2 Command interfaces?
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