asListOrEmpty<T> method

List<T> asListOrEmpty<T>(T map(RequiredPick), { T whenNull(Pick pick)?, })

Returns the picked value as List or an empty list when the value isn't a List or isAbsent.

Each item in the list gets mapped, even when the list contains null values. To simplify the api, only non-null values get mapped with the map function. By default, null values are ignored. To explicitly map null values, use the whenNull mapping function.

final persons = pick([
  {'name': 'John Snow'},
  {'name': 'Daenerys Targaryen'},
  null, // <-- valid value
]).asListOrThrow(
  (pick) => Person.fromPick(pick),
  whenNull: (it) => null,
)

// persons
[
  Person(name: 'John Snow'),
  Person(name: 'Daenerys Targaryen'),
  null,
]

For some apis it is important to get the access to the index of an element in the list. Access it via index which is only available for list elements, otherwise null.

Usage:

pick(["John", "Paul", "George", "Ringo"]).asListOrThrow((pick) {
 final index = pick.index!;
 return Artist(id: index, name: pick.asStringOrThrow());
);

Implementation

List<T> asListOrEmpty<T>(
  T Function(RequiredPick) map, {
  T Function(Pick pick)? whenNull,
}) {
  if (value == null) return <T>[];
  if (value is! List) return <T>[];
  return _parse(map, whenNull: whenNull);
}