In Dart, does `List.unmodifiable` create an unmodifiable view, or a whole new independent list?

Question

1. In Dart, do List.unmodifiable(someList) and Map.unmodifiable(someMap) create an unmodifiable view, or a whole new independent list/map? I am guessing it's a new independent list, but I must be sure.
   • If it's a view, modifications to the original list will modify the now not so unmodifiable list, but sometimes you are just discarding the original anyway, and creating a view is much faster.
2. And, in case they create independent lists/maps, is there some way to create an unmodifiable view, for performance purposes?
   • Update: Ok, I have answered my own question number 2, by finding this: UnmodifiableListView<E> Docs. But I still need to know the answer to the other questions.
3. What's the Big O for creating a dart list from another one, including the one created by List.unmodifiable(someList)? For example, this is the info for Java collections: Big O for Java Collections.

Answer 1

1. The items are copied. It's a whole new independent list.
2. See Dart Collection Library, more specifically:
   • UnmodifiableListView
   • UnmodifiableMapView
3. It's O(N) – it copies all elements, so it has to visit each element.
   • If you use List.unmodifiable from another list, it knows the target length, so it won't have to resize the list it's creating as it's iterating.