Enumerar controles formulario

gistfile1.cs

public static IEnumerable<T> GetAllControls<T>(this Control @this) where T : Control
{    
    return @this.Controls.AsEnumerable()
       .Where(x => x.GetType() == typeof(T))
       .Select(y=>(T)y)
       .Union(@this.Controls.AsEnumerable()
           .SelectMany(x => GetAllControls<T>(x))
           .Select(y=>(T)y));
}