What does it mean when a Type name is “_Closure$__1”?

Question

I have a method that I'm using to output all the class names in an Assembly:

private static void ListClasses()
{
    var assembly = Assembly.LoadFile(@"path\to\my.dll");
    Type[] types = assembly.GetTypes().Where(t => t.IsClass).ToArray();

    using (StreamWriter w = File.AppendText("log.txt"))
    {
        foreach (var type in types)
        {
            w.WriteLine(type.Namespace + "," + type.Name);
            w.Flush();
        }

        w.Close();
    }

    Console.WriteLine("Done");
}

The only problem I'm seeing is some of the class names have this output:

The.Namespace,_Closure$__1

The last number will increment each time the Type name needs to be output this way. Can anyone shed some light as to what this means?

Answer 1

Those are compiler generated classes used by lambda expressions to capture free variables in the lambda expression.

http://msdn.microsoft.com/en-us/library/bb981314%28v=vs.80%29.aspx

Answer 2

A closure is when a local variable is persisted beyond its scope. For example:

public IEnumerable<Employee> GetEmployees(string lastName)
{
    return employees.Where(e => e.LastName == lastName);
}

Compiling this will result in closure, where the lastName will keep its value behind the scenes until the Where is evaluated.

For more information: http://en.wikipedia.org/wiki/Closure_(computer_science )