Readonly wrapper of a LinkedList. HowTo?

Question

Hello. .NET v2

When the List has a very useful (4 me) method AsReadOnly() the LinkedList does not have such a method.

Is there a way to "quickly" interface an internal LinkedList to read only from the external code?

Answer 1

Why not just return a IEnumerable<T>? If you just want to let users enumerate the list without modifying it*, IEnumerable is the obvious choice.

If you want to have a read only interface of the LinkedList interface, you can wrap LinkedList, forward read only methods to the wrapped list and deny any changes.

*) Keep in mind that neither ReadOnlyCollection not IEnumerable will prevent callers to change state of objects in case of a collection of reference types. If the objects should be read only as well, you need to implement this as part of their type.

Answer 2

LinkedList<T> doesn't implement IList so in short, no there is no way of quickly doing it. If you cast your LinkedList to a List you will probably lose the functionality you require.

LinkedList<T> doesn't offer you anything for subclassing so you'll need to write your own. I imagine the next request is "can you show me how to do that"

Answer 3

ReadOnlyCollection<T> takes an IList<T> as argument to the constructor. LinkedList<T> does not implement this interface. List<T> has a constructor overload that takes an IEnumerable<T> as argument, and LinkedList<T> implements this interface. So the following should work:

LinkedList<int> linked = new LinkedList<int>();
// populate the list

ReadOnlyCollection<int> readOnly = new ReadOnlyCollection<int>(
    new List<int>(linked));

It uses an instance of List<T> to carry the items into the ReadOnlyCollection<T> constructor.