using System;

using System.Collections;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var l = Foo().ToList();

        l.Add(Foo());

        Console.WriteLine(string.Join("/", l));

    }

    public static string Foo() => "Hello World";

}

​

public static class ExtensionsOfT

{

    public static List<T> ToList<T>(this T t) => new List<T>();

}