C# TakeLast Extension for .Net Framework 4.6 and newer versions

Question

I'm looking for help finding an extension method for TakeLast that someone has written that can work for older versions of .Net Framework like 4.6 and higher. The default TakeLast method only works with my project for .Net 5 and .Net 6 but I'm trying to allow my program to be run on .Net Framework and the only thing I haven't been able to figure out is how to workaround the lack of TakeLast

Answer 1

You can implement your own extension method, something like this:

public static partial class EnumearbleExtensions {
  public static IEnumerable<T> TakeLast<T>(this IEnumerable<T> source, int count) {
    if (null == source)
      throw new ArgumentNullException(nameof(source));
    if (count < 0)
      throw new ArgumentOutOfRangeException(nameof(count));

    if (0 == count)
      yield break;

    // Optimization (see JonasH's comment)
    if (source is ICollection<T>) {
      foreach (T item in source.Skip(((ICollection<T>)source).Count - count))
        yield return item;

      yield break;
    }

    if (source is IReadOnlyCollection<T>) {
      foreach (T item in source.Skip(((IReadOnlyCollection<T>)source).Count - count))
        yield return item;

      yield break;
    }

    // General case, we have to enumerate source
    Queue<T> result = new Queue<T>();

    foreach (T item in source) {
      if (result.Count == count)
        result.Dequeue();

      result.Enqueue(item);
    }

    foreach (T item in result)
      yield return result.Dequeue();
  }
}