Question

Something like String.Join(",", new string[] { "a", "b" });, but for Guid[]

var guids = new Guid[] { Guid.Empty, Guid.Empty };

var str = /* Magic */

// str = 00000000-0000-0000-0000-000000000000,00000000-0000-0000-0000-000000000000

Answer 1

var str = guids.Select(g => g.ToString())
               .Aggregate((working, next) => working + "," + next);

Once your list of Guids starts growing, this method of concatenation is going to cause performance issues. You can modify it to use a StringBuilder:

var str = guids.Select(g => g.ToString())
               .Aggregate(new StringBuilder(),
                          (sb, str) => sb.Append("," + str),
                          sb => sb.ToString());

Both of those are the complicated LINQ Extension method way of doing things. You could also simply use String.Join:

var str = String.Join(",", guids.Select(g => g.ToString()).ToArray());