method

checkValidRange

Source

/**
 * Check that a range represents a slice of an indexable object.
 *
 * Throws if the range is not valid for an indexable object with
 * the given [length].
 * A range is valid for an indexable object with a given [length]
 *
 * if `0 <= [start] <= [end] <= [length]`.
 * An `end` of `null` is considered equivalent to `length`.
 *
 * The [startName] and [endName] defaults to `"start"` and `"end"`,
 * respectively.
 *
 * Returns the actual `end` value, which is `length` if `end` is `null`,
 * and `end` otherwise.
 */
static int checkValidRange(int start, int end, int length,
                            [String startName, String endName,
                             String message]) {
  // Comparing with `0` as receiver produces better dart2js type inference.
  // Ditto `start > end` below.
  if (0 > start || start > length) {
    if (startName == null) startName = "start";
    throw new RangeError.range(start, 0, length, startName, message);
  }
  if (end != null) {
    if (start > end || end > length) {
      if (endName == null) endName = "end";
      throw new RangeError.range(end, start, length, endName, message);
    }
    return end;
  }
  return length;
}