IReadOnlyListExtensionMethods.cs

using System.Collections.Generic;

namespace Kogane
{
    public static class IReadOnlyListExtensionMethods
    {
        public static T[] ShiftRight<T>
        (
            this IReadOnlyList<T> self,
            int                   shiftCount
        )
        {
            var count  = self.Count;
            var result = new T[ count ];

            for ( var i = 0; i < count; i++ )
            {
                result[ i ] = self[ ( i - shiftCount + count ) % count ];
            }

            return result;
        }

        public static T[] ShiftLeft<T>
        (
            this IReadOnlyList<T> self,
            int                   shiftCount
        )
        {
            var count  = self.Count;
            var result = new T[ count ];

            for ( var i = 0; i < count; i++ )
            {
                result[ i ] = self[ ( i + shiftCount ) % count ];
            }

            return result;
        }
    }
}