3rdpartylibs/fastreports.wpf/FastReport.Forms.WPF/Controls/CheckedListBox.CheckedIndexCollection.cs

using System.Collections;

namespace System.Windows.Forms
{
    public partial class CheckedListBox
    {
        public class CheckedIndexCollection : CollectionBase
        {
            private static string message = "Collection is read only.";

            public int this[int index] => (int)List[index];

            internal void Add(int index) => List.Add(index);

            public new void Clear() => throw new NotSupportedException(message);

            public new void RemoveAt(int index) => throw new NotSupportedException(message);
        }
    }
}