IEnumerable<T>.Concat -- A replacement that can work without changing the reference?

Question

Hello, I've recently been bitten by the (way too commmon in my opinion) gotcha of Concat returns it's result, rather than appending to the list itself.

For instance.

List<Control> mylist=new List<Control>;
//.... after adding Controls into mylist
MyPanel.Controls.Concat(mylist); //This will not affect MyPanel.Controls at all.

MyPanel.Controls=MyPanel.Controls.Concat(mylist); //This is what is needed, but the Controls reference can not be reassigned (for good reason)

So is there some other way of combining two lists that will work when the collection reference is read-only?

Is the only way to do this with a foreach?

foreach(var item in mylist){
  MyPanel.Controls.Add(item);
}

Is there a better way without the foreach?

Answer 1

In the off-chance you prefer capitalized ForEach over lowercase foreach:

mylist.ForEach(MyPanel.Controls.Add); 

Answer 2

Many collections have an AddRange method, winforms ControlCollection is one of them.

MyPanel.Controls.AddRange(mylist.ToArray());

This has the benefit of telling the container you'll be adding many controls at once, so it may delay layout steps until it's done adding all of them.

Answer 3

Your question asks about IEnumerable, and the answer to that is always "No" - an IEnumerable is a forward-only "stream" of items.

However, if you can use a more Specialized type - ICollection, IList etc. - then you can use the Add or AddRange methods if available.

Answer 4

public static void AddRange<T>(this ICollection<T> collection, IEnumerable<T> items) {
    foreach(T item in items) collection.Add(item);
}

Then you have:

anyGenericCollection.AddRange(someSequence);

Of course some collections (List<T>, ControlCollection etc) already have an AddRange - this simply makes it available to those that don't.