inclusive function

Iterable<int> inclusive(int a, [ int? b, int? step ])

Generates an inclusive List of integers. inclusive(3) returns (0, 1, 2, 3). inclusive(-3) returns (-3, -2, -1, 0).

inclusive(1, 3) returns (1, 2, 3). inclusive(-3, -1) returns (-3, -2, -1). inclusive(0, -3) returns (0, -1, -2, -3).

Optional step must be positive if a < b, negative if a > b. inclusive(1, 3, 2) returns (1, 3). inclusive(-3, 1, 2) returns (-3, -1, 1). inclusive(1, -3, -2) returns (1, -1, -3).

Implementation

Iterable<int> inclusive(int a, [int? b, int? step]) sync* {
  // Only one argument given
  if (b == null) {
    if (a >= 0) {
      for (int i = 0; i <= a; i++) {
        yield i;
      }
    } else {
      for (int i = a; i <= 0; i++) {
        yield i;
      }
    }
    return;
  }

  if (a < b) {
    if (step != null && step <= 0) {
      throw ArgumentError('step must be positive if beginning < end');
    }
    for (int i = a; i <= b; i += step ?? 1) {
      yield i;
    }
  } else if (a > b) {
    if (step != null && step >= 0) {
      throw ArgumentError('step must be negative if beginning > end');
    }
    for (int i = a; i >= b; i += step ?? -1) {
      yield i;
    }
  } else {
    yield a;
  }
}