main.dart

class Foo {
  int bar;
  Foo(this.bar);
}

void main() {
  var data = List.generate(10_000_000, (i) => Foo(i));
  // Imutable
  final t1 = DateTime.now();
  data = [for (final i in data) Foo(i.bar + 1)];

  // Mutate
  final t2 = DateTime.now();
  for (final i in data) {
    i.bar += 1;
  }
  final t3 = DateTime.now();
  print("Copy took ${t2.difference(t1).inMilliseconds}ms");
  print("Mutate took ${t3.difference(t2).inMilliseconds}ms");
}