What are unmodifiable and immutable collections in Dart, and why might you deliberately choose to use one instead of a regular mutable collection in certain parts of your code?

An unmodifiable collection, created using a constructor such as List.unmodifiable, throws an error if any code ever attempts to modify it after its initial creation, such as adding or removing an item, and deliberately using unmodifiable collections in appropriate places, such as when exposing a private internal list publicly from a class, helps prevent unintended external modification of data that should genuinely remain fixed and protected, catching an accidental mutation mistake early with a clear error rather than allowing silent, unexpected changes to data elsewhere in a large codebase.

class ShoppingCart {
  final List<String> _items = [];
  List<String> get items => List.unmodifiable(_items);
}