Using LINQ extension method syntax on a MatchCollection

using System.Linq;

matches.Cast<Match>().Any(x => x.Groups["name"].Value.Length > 128)

You just need to convert it from an IEnumerable to an IEnumerable<Match> (IEnumerable<T>) to get access to the LINQ extension provided on IEnumerable<T>.

When you specify an explicit range variable type, the compiler inserts a call to Cast<T>. So this:

bool result = (from Match m in matches
               where m.Groups["name"].Value.Length > 128
               select m).Any();

is exactly equivalent to:

bool result = matches.Cast<Match>()
                     .Where(m => m.Groups["name"].Value.Length > 128)
                     .Any();

which can also be written as:

bool result = matches.Cast<Match>()
                     .Any(m => m.Groups["name"].Value.Length > 128);

In this case the Cast call is required because MatchCollection only implements ICollection and IEnumerable, not IEnumerable<T>. Almost all the LINQ to Objects extension methods are targeted at IEnumerable<T>, with the notable exceptions of Cast and OfType, both of which are used to convert a "weakly" typed collection (such as MatchCollection) into a generic IEnumerable<T> - which then allows for further LINQ operations.