ValueOrAbsent<T> class sealed

Distinguishes an omitted copy value from an explicit replacement value.

This is useful for copyWith methods where a nullable field must be able to keep its current value, change to a non-null value, or change to null.

class Example {
  const Example({this.name});

  final String? name;

  Example copyWith({
    ValueOrAbsent<String?> name = const ValueOrAbsent.absent(),
  }) =>
      Example(name: name.valueOr(this.name));
}

example.copyWith(); // keep existing name
example.copyWith(name: ValueOrAbsent.value('room')); // set name
example.copyWith(name: ValueOrAbsent.value(null)); // clear name

Experimental: this API may change in a future release.