using System;

using static System.Console;

​

public class Program {

    public static void Main() {

        var x = new Exemplo();

        x.handler("http://dominio.br/pagina.html");

        x.handler = Write;

        x.handler("http://dominio.br/pagina.html");

        Write("Fim");

    }

    class Exemplo {

         public Action<string> handler = WriteLine;

    }

}