using System;

public class Counter {

    public readonly int Value;

    public Counter(int x) {

        this.Value = x;

    }

    public Counter Increase() {

        return new Counter(this.Value + 1);

    }

}

​

var cnt  = new Counter(0);

var cnt2 = cnt.Increase().Increase();

​

Console.WriteLine(cnt.Value);

Console.WriteLine(cnt2.Value);