Why there isn't a ReadOnlyList<T> class in the System.Collections library of C#?

Reading about the probl开发者_开发百科em of creating a read only primitive vector in C# (basically, you cannot do that),

public readonly int[] Vector = new int[]{ 1, 2, 3, 4, 5 }; // You can still changes values

I learnt about ReadOnlyCollectionBase. This is a base class for containers of objects that let their positions be accessed but not modified. Even there is an example in Microsoft Docs.

ReadOnlyCollectionBase Class - Microsoft Docs

I slightly modified the example to use any type:

public class ReadOnlyList<T> : ReadOnlyCollectionBase {
    public ReadOnlyList(IList sourceList)  {
      InnerList.AddRange( sourceList );
    }

    public T this[int index]  {
      get  {
         return( (T) InnerList[ index ] );
      }
    }

    public int IndexOf(T value)  {
      return( InnerList.IndexOf( value ) );
    }



    public bool Contains(T value)  {
      return( InnerList.Contains( value ) );
    }

}

... and it works. My question is, why does not exist this class in the standard library of C#, probably in System.Collections.Generic? Am I missing it? Where is it? Thank you.

---

There is ReadOnlyCollection<T>, which is the generic version of the above.

You can create one from a List<T> directly by calling list.AsReadOnly().