Question

How would you implement a capacity-limited, generic MruList in C# or Java?

I want to have a class that represents a most-recently-used cache or list (= MruList). It should be generic, and limited to a capacity (count) specified at instantiation. I’d like the interface to be something like:

public interface IMruList<T>
{
    public T Store(T item);
    public void Clear();
    public void StoreRange(T[] range);
    public List<T> GetList();
    public T GetNext(); // cursor-based retrieval
} 

Each Store() should put the item at the top (front?) of the list. The GetList() should return all items in an ordered list, ordered by most recent store. If I call Store() 20 times and my list is 10 items long, I only want to retain the 10 most-recently Stored items. The GetList and StoreRange is intended to support retrieval/save of the MruList on app start and shutdown.

This is to support a GUI app.
I guess I might also want to know the timestamp on a stored item. Maybe. Not sure.

Internally, how would you implement it, and why?

(no, this is not a course assignment)

Answer 1

Couple of comments about your approach

• Why have Store return T? I know what I just added, returning it back to me is un-necessary unless you explicitly want method chaining
• Refactor GetNext() into a new class. It represents a different set of functionality (storage vs. cursor traversal) and should be represented by a separate interface. It also has usability concerns as what happens when two different methods active on the same stack want to traverse the structure?
• GetList() should likely return IEnumerable<T>. Returning List<T> either forces an explicit copy up front or returns a pointer to an underlying implementation. Neither is a great choice.

As for what is the best structure to back the interface. It seems like the best to implement is to have a data structure which is efficient at adding to one end, and removing from the other. A doubly linked list would suit this nicely.