AddRange to a Collection
A coworker asked me today how to add a range to a collection. He has a class that inherits from Collection<T>
. 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<T>
-style AddRange would be far more elegant.
It's easy enough to write an extension method:
public static class CollectionHelpers
{
public static void AddRange<T>(this ICollection<T> destination,
IEnumerable<T> 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 morelinq.
Bad design? Just Call Add? Missing the obvious?
No, this seems perfectly reasonable. There is a List<T>.
AddRange() method that basically does just this, but requires your collection to be a concrete List<T>
.
Try casting to List in the extension method before running the loop. That way you can take advantage of the performance of List.AddRange.
public static void AddRange<T>(this ICollection<T> destination,
IEnumerable<T> source)
{
List<T> list = destination as List<T>;
if (list != null)
{
list.AddRange(source);
}
else
{
foreach (T item in source)
{
destination.Add(item);
}
}
}
Remember that each Add
will check the capacity of the collection and resize it whenever necessary (slower). With AddRange
, the collection will be set the capacity and then added the items (faster). This extension method will be extremely slow, but will work.
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