I want to pass vararg from the buy function to the drive function but I get
a compile error:
required Array<T> found Array<out T>
code:
class Car
fun buy(vararg cars: Car) {
drive(cars) //compile error
}
fun drive(cars: Array<Car>) {
//...
}
The precise error is:
Type mismatch.
Required: Array<Car>
Found: Array<out Car>
The problem is that when you have a vararg cars: Car function parameter, its type inside the function is Array<out Car>, which basically represents a read-only array of the arguments the function was called with - after all, it wouldn't really be a nice thing to start modifying the arguments you got as a vararg (function parameters in Kotlin are read-only vals, and this is something very similar).
But your drive function requires a regular Array<Car>, which of course is writable as well. So if you wish to keep these function signatures, you'll need to create a new array that contains everything from your read-only array. This can be created using the following syntax:
drive(arrayOf(*cars))
This calls the arrayOf function we usually create arrays with, which takes a vararg parameter, and uses the spread operator which is a way to pass in the elements of an array (which cars is, inside the buy function) as the vararg parameters (docs here).
While all this may sound complicated, it's actually a very efficient solution, as it just uses Array.copyOf under the hood in the bytecode.
Array<out Car> as the parameter for the second function, not make a copy.Another solution would be to change drive to fun drive(Array<out Car>) { ... }. This of course means that the cars inside drive cannot be modified but avoids the copying.
fun foo(vararg strings: String): Array<out String> {
return strings
}
// Define a var
var yourVar: Array<out String> = foo("a", "b", "c")
// Use var in Java method `public void javaMethod(String... someParam)() {}`
javaMethod(*yourVar)
override fun checkMatch(vararg cards: SetsCard): Int {
return if (isSet(*cards)) 16 else -2
}
private fun isSet(vararg cards: SetsCard) : Boolean {
if (cards.size == 3) {
return true
}
return false
}
Essencially you need the vararg keywork before the variable name.
fun args(vararg cars: Car) {
//use cars as an array
}
