string reverse - C# - various ways

stringReverse_variousways1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace stringArray
{
    class Program
    {
        static void Main(string[] args)
        {
            string test = "abcd";
            string result = Reverse_6(test); 
        }

        public static string Reverse(string s)
        {
            char[] charArray = s.ToCharArray();
            Array.Reverse(charArray);
            return new string(charArray);
        }

        /*
         * Enumerable.Reverse 
         * string.Concat
         * 
         * 
         */
        public static string stringReverse_2(string s)
        {            
            return string.Concat(Enumerable.Reverse(s)); 
        }

        public static string stringReverse_3(string s)
        {
            return new string(s.Reverse().ToArray()); 
        }

        /*
         * string construct - IEnumberable 
         * string.ToCharArray()
         * IEnumerable.Reverse()
         * IEnumerable.ToArray()
         * 
         */
        public static string stringReverse_4(string s)
        {
            return new string(s.ToCharArray().Reverse().ToArray());
        }

        /*
        Firstly you don't need to call ToCharArray as a string can 
        already be indexed as a char array, so this will save you an allocation.

        The next optimisation is to use a StringBuilder to prevent 
        unnecessary allocations (as strings are immutable, concatenating them 
        makes a copy of the string each time). To further optimise this we 
        pre-set the length of the StringBuilder so it won't need to expand 
        its buffer.
         * 
         * string.isNullOrEmtpy
         * string.Empty
         * 
        */
        public string Reverse_5(string text)
        {        
            if (string.IsNullOrEmpty(text))
            {
                return text;
            }

            StringBuilder builder = new StringBuilder(text.Length);
            for (int i = text.Length - 1; i >= 0; i--)
            {
                builder.Append(text[i]);
            }

            return builder.ToString();
        }

        public static string Reverse_6(string text)
        {
            return text.Reverse(); 
        }
    }

    // Of course you can extend string class with Reverse method
    public static class StringExtensions
    {
        public static string Reverse(this string input)
        {
            return string.Concat(Enumerable.Reverse(input));
        }
    }
}