using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Xml;
using System.Xml.Linq;

public static class LocalExtensions
{
    public static string StringConcatenate(
        this IEnumerable<string> source)
    {
        return source.Aggregate(
            new StringBuilder(),
            (s, i) => s.Append(i),
            s => s.ToString());
    }

    public static string StringConcatenate<T>(
        this IEnumerable<T> source,
        Func<T, string> projectionFunc)
    {
        return source.Aggregate(
            new StringBuilder(),
            (s, i) => s.Append(projectionFunc(i)),
            s => s.ToString());
    }
}

class Program
{
    static void Main(string[] args)
    {
        string[] stringList = new[] { "aaa", "bbb", "ccc" };
        XElement xmlDoc = XElement.Parse(
            @"<Root>
                 <Value>111</Value>
                 <Value>222</Value>
                 <Value>333</Value>
              </Root>");

        string s1 = stringList.StringConcatenate();
        string s2 = xmlDoc.Elements().StringConcatenate(el => (string)el);

        Console.WriteLine(s1);
        Console.WriteLine(s2);
    }
}