Comparable arrays in Kotlin
Comparable arrays in Kotlin
Coming from a Swift world I'm trying to figure out how to use comparable functions like min() or max() on an array of objects. In Swift I would use the comparable protocol -
min()
max()
class Car: Comparable {
let year: Int
static func < (lhs: Car, rhs: Car) -> Bool {
return lhs.year < rhs.year
}
static func == (lhs: Car, rhs: Car) -> Bool {
return lhs.year == rhs.year
}
}
But how would you do the same in Kotlin? I've tried this but I'm not sure if it's the right approach, or how I would implement the iterable function -
data class Car(val year: Int): Comparable<Car>, Iterable<Car> {
override fun compareTo(other: Car) = when {
this.year < other.year -> -1
this.year > other.year -> 1
else -> 0
}
override fun iterator(): Iterator<Car> {
TODO("not implemented")
}
}
min
max
Comparable
this.year - other.year
The
compareTo method looks fine, but you don't need the car to be an Iterable. That doesn't make any sense.– marstran
Jul 1 at 16:57
compareTo
Iterable
1 Answer
1
Regarding your implementation there's no issue, but you could make it simpler:
data class Car(val year: Int): Comparable<Car> {
override fun compareTo(other: Car) = year - other.year
}
You should not implement the Iterable interface, because this would make the Car a kind of a collection.
Iterable
Car
Running the following example with the given Car implementation
Car
listOf(Car(2004), Car(2007), Car(2001)).run {
println(this)
println(min())
println(max())
println(sorted())
}
yields the output of
[Car(year=2004), Car(year=2007), Car(year=2001)]
Car(year=2001)
Car(year=2007)
[Car(year=2001), Car(year=2004), Car(year=2007)]
Right ok. I think it's the
run bit I was missing. I was trying to call max() on the list directly listOf(Car(2004), Car(2007), Car(2001)).max() which I could only do if I implemented the Iterable interface.– Chris Edgington
Jul 1 at 17:49
run
max()
listOf(Car(2004), Car(2007), Car(2001)).max()
Iterable
There is actually no difference and your code there runs fine as well. I'd assume you missed a closing brace somewhere and thus the compiler tried to call
max() on a Car.– tynn
Jul 1 at 18:03
max()
Car
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So your end goal is to be able to call
minandmaxon an array of Cars? You can already do that with yourComparableimplementation, although it could be simpler (this.year - other.year).– zsmb13
Jul 1 at 16:56