singleWhere method Null safety

E singleWhere(
  1. bool test(
    1. E element
    ),
  2. {E orElse(
      )?}
    )
    inherited

    Returns the single element that satisfies test.

    Checks elements to see if test(element) returns true. If exactly one element satisfies test, that element is returned. If more than one matching element is found, throws StateError. If no matching element is found, returns the result of orElse. If orElse is omitted, it defaults to throwing a StateError.

    Example:

    final numbers = <int>[2, 2, 10];
var result = numbers.singleWhere((element) => element > 5); // 10

    When no matching element is found, the result of calling orElse is returned instead.

    result = numbers.singleWhere((element) => element == 1,
    orElse: () => -1); // -1

    There must not be more than one matching element.

    result = numbers.singleWhere((element) => element == 2); // Throws Error.

    Implementation

    E singleWhere(bool test(E element), {E Function()? orElse}) {
  int length = this.length;
  late E match;
  bool matchFound = false;
  for (int i = 0; i < length; i++) {
    E element = elementAt(i);
    if (test(element)) {
      if (matchFound) {
        throw IterableElementError.tooMany();
      }
      matchFound = true;
      match = element;
    }
    if (length != this.length) {
      throw ConcurrentModificationError(this);
    }
  }
  if (matchFound) return match;
  if (orElse != null) return orElse();
  throw IterableElementError.noElement();
}