ExtendedActivator.cs

using System;
using System.Linq;
using System.Runtime.InteropServices;

namespace Reflection
{
    public static class ExtendedActivator
    {
        public static object CreateInstance(Type type)
        {
            var constructors = type.GetConstructors();
            var defaultConstructor = constructors.SingleOrDefault(c => !c.GetParameters().Any());
            if (defaultConstructor == null)
            {
                var pseudoDefaultConstructor = constructors.FirstOrDefault(
                    ci => ci.GetParameters().All(
                        p => p.GetCustomAttributes(typeof(OptionalAttribute), false).Any()));
                if (pseudoDefaultConstructor == null)
                    throw new InvalidOperationException("No default constructor found");
                return pseudoDefaultConstructor.Invoke(pseudoDefaultConstructor.GetParameters()
                                                           .Select(p => p.DefaultValue).ToArray());
            }
            return Activator.CreateInstance(type);
        }
    }
}