range function

Iterable<int> range(int startOrEnd, [ int? end, int? step ])

A generator over a range by a step size. If end is not provided, the generated range will be [0..startOrEnd) if startOrEnd > 0, and nothing is generated otherwise. If step is not provided, step will be -1 if 0 > startOrEnd and 1 if 0 < startOrEnd. For reference, it works the same as the python range function.

range(end); // == range(0,end);
range(start, end);
range(start, end, step);

Implementation

// // Dev Note: inlined for parameter optimization
// @pragma("vm:prefer-inline")
Iterable<int> range(int startOrEnd, [int? end, int? step]) sync* {
  assert(!(end == null && step != null),
      "'step' cannot be given if 'end' is null. Step will be ignored in release mode.");
  if (step == 0) {
    panic("'step' cannot be zero");
  }
  if (end == null) {
    int current = 0;
    if (startOrEnd > 0) {
      do {
        yield current;
        current++;
      } while (current < startOrEnd);
    }
    return;
  }
  if (startOrEnd == end) {
    return;
  }
  if (startOrEnd < end) {
    if (step == null) {
      step = 1;
    } else if (step < 0) {
      return;
    }
    do {
      yield startOrEnd;
      startOrEnd += step;
    } while (startOrEnd < end);
  } else {
    if (step == null) {
      step = -1;
    } else if (step > 0) {
      return;
    }
    while (startOrEnd > end) {
      yield startOrEnd;
      startOrEnd += step;
    }
  }
}