Function narrowed

packages/forms/signals/test/node/recursive_logic.spec.ts:20–28

(
  fieldTree: FieldTree<TModel> | undefined,
  guard: (value: TModel) => value is TNarrowed,
)

}

function narrowed<TModel, TNarrowed extends TModel>(
  fieldTree: FieldTree<TModel> | undefined,
  guard: (value: TModel) => value is TNarrowed,
): Signal<FieldTree<TNarrowed> | undefined> {
  return computed(
    () =>
      fieldTree && (guard(fieldTree().value()) ? (fieldTree as FieldTree<TNarrowed>) : undefined),
  );
}

function isNonNull<T>(t: T): t is NonNullable<T> {
  return t !== null;