KeyedCollection is a collection of what?

Question

I want to create a method that would iterate through a keyed collection. I want to make sure that my method support iteration of any collection that extends the KeyedCollection<string, Collection<string>>

Here's the method:

public void IterateCollection(KeyedCollection<string, Collection<string>> items)
{
    foreach (??? item in items)
    {
        Console.WriteLine("Key: " + item.Key);
        Console.WriteLine("Value: " + item.Value);
    }
}

It doesn't work obviously because I don't know which type should replace the question marks in the loop. I cannot simply put object or var because I need to call the Key and Value properties later on in the loop body. What is the type that I am looking for? Thanks.

Answer 1

KeyedCollection<TKey, TItem> implements ICollection<TItem> , so in this case you'd use:

foreach(Collection<string> item in items)

That's what var would give you as well. You don't get key/value pairs in KeyedCollection - you just get the values.

Is it possible that KeyedCollection really isn't the most appropriate type for you to be using?

Answer 2

The item type is going to be Collection<String> by definition of the enumerator of KeyedCollection . You can't arbitrarily decide on using an appropriate type so that you get both Key and Value if the iteration doesn't support it, which it doesn't in this case. Note that using the explicit type and var are exactly identical.

If you want both Key and Value available in iteration, you need to use the Dictionary<string, Collection<string>> type.