Why doesn't IList support AddRange

Question

List.AddRange() exists, but IList.AddRange() doesn\'t.
This strikes me as odd. What\'s the reason behind this?

Answer 1

For those who want to have extension methods for "AddRange", "Sort", ... on IList,

Below is the AddRange extension method:

 public static void AddRange(this IList source, IEnumerable newList)
 {
     if (source == null)
     {
        throw new ArgumentNullException(nameof(source));
     }

     if (newList == null)
     {
        throw new ArgumentNullException(nameof(newList));
     }

     if (source is List concreteList)
     {
        concreteList.AddRange(newList);
        return;
     }

     foreach (var element in newList)
     {
        source.Add(element);
     }
}

I created a small library that does this. I find it more practical than having to redo its extension methods on each project.

Some methods are slower than List but they do the job.

Here is the GitHub to interest them:

IListExtension repository