using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

​

// Demo: Extension Methods

// Note: This must be a console application

​

public static class StringBuilderExtensions

{

    public static StringBuilder AppendFormattedLine(this StringBuilder @this, string format, params object[] args)

    {

        return

            @this

                .AppendFormat(format, args)

                .AppendLine();

    }

    public static StringBuilder AppendSequence<T>(

        this StringBuilder @this,

        IEnumerable<T> seq,

        Func<StringBuilder, T, StringBuilder> fn)

    {

        // Aggregate is LINQ's name for what most functional languages call "Reduce"

        // Iterate over each item in the sequence, applying the supplied function to each item and returning the StringBuilder

        return seq.Aggregate(@this, fn);

    }

}

public class Program

{

    public static void Main()

    {

        var numbers = new [] { 1, 2, 3 };

        var str =

            new StringBuilder()

                .AppendFormattedLine("Hello, {0}!", "Dave");

        StringBuilderExtensions.AppendSequence(str, numbers,(sb,i) => sb.AppendFormattedLine(("\tItem {0}"), i));

                //.AppendSequence(

                //  numbers,

                //  (sb, i) => sb.AppendFormattedLine("\tItem {0}", i))

                //.ToString();      

        Console.WriteLine(str);

    }

}

​