c# - AddRange to a Collection

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A coworker asked me today
how to add a range to a collection. He has a class that inherits from
Collection. There's a get-only property of that type
that already contains some items. He wants to add the items in another collection to the
property collection. How can he do so in a C#3-friendly fashion? (Note the
constraint about the get-only property, which prevents solutions like doing Union and
reassigning.)

Sure, a foreach with
Property. Add will work. But a List-style AddRange
would be far more elegant.

It's easy enough to
write an extension method:

public
            static class CollectionHelpers
{
 public static void
            AddRange(this ICollection destination,
 IEnumerable
            source)

 {
 foreach (T item in source)

            {
 destination.Add(item);
 }

            }
}

But I
have the feeling I'm reinventing the wheel. I didn't find anything similar in
System.Linq or rel="noreferrer">morelinq.

Bad
design? Just Call Add? Missing the obvious?

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class="normal">Answer

No, this
seems perfectly reasonable. There is a List. href="http://msdn.microsoft.com/en-us/library/z883w3dc.aspx"
rel="noreferrer">AddRange() method that basically does just this, but
requires your collection to be a concrete
List.