22 Collection for elements

A collection literal can generate elements from another iterable.

main() {
  List<Integer> source = [1, 2, 3]
  List<Integer> doubled = [
    for (number : source) number * 2
  ]
  for number : doubled {
    printLine(number)
  }
  printLine(doubled.size())
}

Expected output:

2
4
6
3

The parenthesized for head belongs inside []: it contributes number * 2 once per source element. This builds a new list, unlike the statement loop in the iteration lesson.

Try it: Filter the generated list in the next lesson, then compare the outputs.

Precise rules: Reference.