Question

What are the drawbacks of marking a class as serializable?

I need to save my asp.net session in a db and it requires that the objects in the session are serializable.

Make sense.

But turns out that all I had to do was decorate that class with the [Serializable] attribute and it worked, so that means .NET already has the underlying infrastructure to make classes serializable. So why can’t it just do it by default?

What’s the need to mark it as such?

Answer 1

So why can’t it just do it by default?

Automatic serialization/deserialization might not suffice for the object. For example, the object might contain a field that holds the name of a local file, a pointer to memory, an index into a shared array, etc. While the system could typically serialize these raw values without trouble, deserialization could easily result in something that is not usable. In general, it is impossible for the system to figure this out on its own. By requiring you to mark the class with Serializable, you indicate that you have taken these considerations into account.