flatMap<T, R> static method
Maps each element of list through fn, flattening the resulting
iterables into a single list.
Arr.flatMap(pages, (p) => p.items); // all items from all pages
Implementation
static List<R> flatMap<T, R>(Iterable<T> list, Iterable<R> Function(T) fn) =>
[for (final v in list) ...fn(v)];