List<PointerEvent> is a List<dynamic>

main.dart

import 'dart:html';

void main() {
  window.addEventListener('pointermove', handlePointerMove);
}

void handlePointerMove(Event event) {
  final PointerEvent pointerEvent = event;
  final Iterable<Foo> fooList = expandEvent(pointerEvent).expand(
    (PointerEvent e) => getFooListForEvent(e),
  );
  printIterable(fooList);
}

List<PointerEvent> expandEvent(PointerEvent event) {
  final List<PointerEvent> coalescedEvents = event.getCoalescedEvents();
  // Calling `.cast<PointerEvent>()` fixes the issue.
  return coalescedEvents/* .cast<PointerEvent>() */;
}

List<Foo> getFooListForEvent(PointerEvent event) {
  return <Foo>[Foo(event.client.x), Foo(event.client.y)];
}

void printIterable(Iterable<Foo> foos) {
  for (Foo foo in foos) {
    print(foo);
  }
}

class Foo {
  double _value;

  Foo(this._value);
  
  String toString() => _value.toString();
}