plus
and minus
Operators
In Kotlin, plus
(+
) and minus
(-
) operators are defined for collections. They take a collection as the first operand; the second operand can be either an element or another collection. The return value is a new read-only collection:
- The result of
plus
contains the elements from the original collection and from the second operand. - The result of
minus
contains the elements of the original collection except the elements from the second operand. If it’s an element,minus
removes its first occurrence; if it’s a collection, all occurrences of its elements are removed.
fun main() {
//sampleStart
val numbers = listOf("one", "two", "three", "four")
val plusList = numbers + "five"
val minusList = numbers - listOf("three", "four")
println(plusList)
println(minusList)
//sampleEnd
}
For the details on plus
and minus
operators for maps, see Map Specific Operations. The augmented assignment operators plusAssign
(+=
) and minusAssign
(-=
) are also defined for collections. However, for read-only collections, they actually use the plus
or minus
operators and try to assign the result to the same variable. Thus, they are available only on var
read-only collections. For mutable collections, they modify the collection if it’s a val
. For more details see Collection Write Operations.