Say Hello to Kotlin Sequence

In some case, sequence operation is faster than collection operation.

val list1 = (1..10_000_000)
    .filter { it % 2 == 0 }
    .map { it * 10 }
    .map { it.toString() }
    .size // 5,000,000
// took 1,263 milliseconds in my environment

val list2 = (1..10_000_000)
    .asSequence()
    .filter { it % 2 == 0 }
    .map { it * 10 }
    .map { it.toString() }
    .toList()
    .size // 5,000,000
// took 1,015 milliseconds in my environment

In this case, you can create Sequence directly like this:

val list3 = generateSequence(1) { it + 1 }
    .take(10_000_000)
    .filter { it % 2 == 0 }
    .map { it * 10 }
    .map { it.toString() }
    .toList()
    .size // 5,000,000
// took 861 milliseconds in my environment

Sequence executes lazily and does not create intermediate products.

Sequence need some overhead, so be care it is not always faster than Collection.