void IList.RemoveAt(int index) => ThrowHelper.ThrowCollectionIsReadonly();
 void IList.Remove(object value) => ThrowHelper.ThrowCollectionIsReadonly();
 void IList.Insert(int index, object value) => ThrowHelper.ThrowCollectionIsReadonly();
 void IList.Clear() => ThrowHelper.ThrowCollectionIsReadonly();
 int IList.Add(object value) => ThrowHelper.ThrowCollectionIsReadonly <int>();
 object IList.this[int index]
 {
     get { return(this[index]); }
     set { ThrowHelper.ThrowCollectionIsReadonly(); }
 }