traverse<A extends Object, B extends Object> function

List<B>? traverse<A extends Object, B extends Object>(List<A?> xa, Func1<A, B?> f)

Maps over the list and applies f to each non-null element. Returns the list of non-null values if all elements and results of applying f are not null, otherwise returns null.

Implementation

List<B>? traverse<A extends Object, B extends Object>(
  List<A?> xa,
  Func1<A, B?> f,
) {
  final List<B> result = [];

  for (final a in xa) {
    if (a == null) return null;
    final b = f(a);
    if (b == null) return null;

    result.add(b);
  }

  return result;
}