single method

T single([ bool predicate(T)? ])

Returns the single element matching the given predicate, or throws an exception if the list is empty or has more than one element.

Implementation

T single([bool Function(T)? predicate]) {
  if (predicate == null) {
    final i = iterator();
    if (!i.hasNext()) {
      throw const NoSuchElementException("Collection is empty.");
    }
    final single = i.next();
    if (i.hasNext()) {
      throw ArgumentError("Collection has more than one element.");
    }
    return single;
  } else {
    T? single;
    var found = false;
    for (final element in iter) {
      if (predicate(element)) {
        if (found) {
          throw ArgumentError(
              "Collection contains more than one matching element.");
        }
        single = element;
        found = true;
      }
    }
    if (!found) {
      throw const NoSuchElementException(
          "Collection contains no element matching the predicate.");
    }
    return single!;
  }
}