Extension interface patterns

Question

The new extensions in .Net 3.5 allow functionality to be split out from interfaces.

For instance in .Net 2.0

public interface IHaveChildren {
    str         


        

Answer 1

I needed to solve something similar: I wanted to have a List passed to the extensions function where IIDable is an interface that has a long getId() function. I tried using GetIds(this List bla) but the compiler didn't allow me to do so. I used templates instead and then type casted inside the function to the interface type. I needed this function for some linq to sql generated classes.

I hope this helps :)

    public static List GetIds(this List original){
        List ret = new List();
        if (original == null)
            return ret;

        try
        {
            foreach (T t in original)
            {
                IIDable idable = (IIDable)t;
                ret.Add(idable.getId());
            }
            return ret;
        }
        catch (Exception)
        {
            throw new Exception("Class calling this extension must implement IIDable interface");
        }