using System;

using System.Collections;

​

public interface IRefEnumerator<T> : IEnumerator, IDisposable

{

    new ref T Current { get; }

}

public interface IRefEnumerable<T>

{

    public IRefEnumerator<T> GetEnumerator();

}

public class ArrayEnumerable<T> : IRefEnumerable<T>

{

    private T[] _data;

    public ArrayEnumerable(T[] data) => _data = data ?? throw new ArgumentNullException(nameof(data));

    private class ArrayEnumerator<T> : IRefEnumerator<T>

    {

        private T[] _data;

        private int _pos = -1;

        public ArrayEnumerator(T[] data) => _data = data ?? throw new ArgumentNullException(nameof(data));

        public ref T Current {

            get

            {

                return ref _data[_pos];

            }

        }

​

        object IEnumerator.Current => _data[_pos];

        public void Dispose() { }

        public bool MoveNext() => ++_pos < _data.Length;

        public void Reset() => _pos = -1;

    }

    public IRefEnumerator<T> GetEnumerator() => new ArrayEnumerator<T>(_data);

}

public static class ArrayEnumerable

{

    public static ArrayEnumerable<T> AsRefEnumerable<T>(this T[] data) => new ArrayEnumerable<T>(data);

}

​

​

class Program

{

    public static void Main()

    {

        int[] a = {1,2,3,4,5};

        foreach(ref var x in a.AsRefEnumerable())

        {

            x = 10;

        }

        Console.WriteLine(string.Join(",", a));

    }

}