AddRange to a Collection
C#CollectionsC# 3.0Extension MethodsC# Problem Overview
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?
C# Solutions
Solution 1 - C#
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>
.
Solution 2 - C#
Try casting to List
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);
}
}
}
Solution 3 - C#
Since .NET4.5
if you want one-liner you can use System.Collections.Generic
ForEach.
source.ForEach(o => destination.Add(o));
or even shorter as
source.ForEach(destination.Add);
Performance-wise it's the same as for each loop (syntactic sugar).
Also don't try assigning it like
var x = source.ForEach(destination.Add)
cause ForEach
is void.
Edit: Copied from comments, Lippert's opinion on ForEach.
Solution 4 - C#
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.
Solution 5 - C#
Here is a bit more advanced/production-ready version:
public static class CollectionExtensions
{
public static TCol AddRange<TCol, TItem>(this TCol destination, IEnumerable<TItem> source)
where TCol : ICollection<TItem>
{
if(destination == null) throw new ArgumentNullException(nameof(destination));
if(source == null) throw new ArgumentNullException(nameof(source));
// don't cast to IList to prevent recursion
if (destination is List<TItem> list)
{
list.AddRange(source);
return destination;
}
foreach (var item in source)
{
destination.Add(item);
}
return destination;
}
}
Solution 6 - C#
The C5 Generic Collections Library classes all support the AddRange
method. C5 has a much more robust interface that actually exposes all of the features of its underlying implementations and is interface-compatible with the System.Collections.Generic
ICollection
and IList
interfaces, meaning that C5
's collections can be easily substituted as the underlying implementation.
Solution 7 - C#
You could add your IEnumerable range to a list then set the ICollection = to the list.
IEnumerable<T> source;
List<item> list = new List<item>();
list.AddRange(source);
ICollection<item> destination = list;
Solution 8 - C#
Or you can just make an ICollection extension like this:
public static ICollection<T> AddRange<T>(this ICollection<T> @this, IEnumerable<T> items)
{
foreach(var item in items)
{
@this.Add(item);
}
return @this;
}
Using it would be just like using it on a list:
collectionA.AddRange(IEnumerable<object> items);
Solution 9 - C#
Agree with some guys above and Lipert's opinion. In my case, it's quite often to do like this:
ICollection<int> A;
var B = new List<int> {1,2,3,4,5};
B.ForEach(A.Add);
To have an extension method for such operation a bit redundant in my view.