Kotlin Ranges


Introduction

Range expressions are formed with rangeTo functions that have the operator form .. which is complemented by in and !in. Range is defined for any comparable type, but for integral primitive types it has an optimized implementation

Integral Type Ranges

Integral type ranges ( IntRange , LongRange , CharRange ) have an extra feature: they can be iterated over. The compiler takes care of converting this analogously to Java's indexed for-loop, without extra overhead

for (i in 1..4) print(i) // prints "1234"
for (i in 4..1) print(i) // prints nothing

downTo() function

if you want to iterate over numbers in reverse order? It's simple. You can use the downTo() function defined in the standard library

for (i in 4 downTo 1) print(i) // prints "4321"

step() function

Is it possible to iterate over numbers with arbitrary step, not equal to 1? Sure, the step() function will help you

for (i in 1..4 step 2) print(i) // prints "13"
for (i in 4 downTo 1 step 2) print(i) // prints "42"

until function

To create a range which does not include its end element, you can use the until function:

for (i in 1 until 10) { // i in [1, 10), 10 is excluded
println(i)
}