T in class? AddRange ICollection?

I try to do static class, add to icollection but i got some issues i ca开发者_Go百科nt seem to overcome. that is how i get so i can pass a ICollection in the method? cause T is that say it can not be resolved.

and then i wonder is there a way to do AddRange on icollection?

i was thinking of something like this but maby i am way out of my mind with it?

public static ICollection<T> add(this IEnumerable<T> list)
    {
        ICollection<T> collection = null;

        return collection.AddRange(list);            
    }

No, ICollection<T> doesn't have an AddRange method - and even if it did, you'd be trying to dereference null which will throw a NullReferenceException. You haven't specified a collection to add the list to... what exactly are you trying to do?

You could create (say) a new List<T> - and that has the benefit of already having a constructor which can take an IEnumerable<T>:

public static ICollection<T> Add<T>(this IEnumerable<T> list)
{
    return new List<T>(list);            
}

However, at that point you've really just reimplemented Enumerable.ToList() and given it a different return type...

If you want to add everything to an existing collection, you might want something like this:

public static ICollection<T> AddTo<T>(this IEnumerable<T> list,
                                      ICollection<T> collection)
{
    foreach (T item in list)
    {
        collection.Add(item);
    }
    return collection;
}

If I understand correctly you want to add a IEnumerable<T> to an empty collection.

Wouldn't it be easier to just do:

ICollection<MyObject> collection = new List<MyObject>(GetIEnumerableOfMyObject());

Or even:

ICollection<MyObject> collection = GetIEnumerableOfMyObject().ToList();

The other ways seem to assume that your ICollection is empty and/or your ICollection is a type of List. However, if you want AddRange, then you can Extend the ICollection class as follows:

public static void AddRange<T>(this ICollection<T> ic, IEnumerable<T> ie)
{
    foreach (T obj in ie)
    {
        ic.Add(obj);
    }
}

Note, however, that since List impliments ICollection, this may cause ambiguity when dealing directly with List objects (though I haven't tested yet if the compiler will be able to resolve it--my gut reaction is that it should, though, since AddRange is a member of List and the compiler will go through member functions first before looking at extensions, but if I'm wrong I'm sure someone will correct me).

Depending on the collection type of your source list an alternative approach is to use List(T).ForEach, as in:

List<string> source = ...
ICollection<string> dest = ...

source.Foreach(dest.Add);

However, the readability of this is easy to dispute.