What is a serializable object?

Question

What is a serializable object in C#? I guess the word serializable is throwing me off more than "serializable object".

Answer 1

Normally objects are random access, that is, you can specify any part of an object (property or field) and access that part directly. That's all well and fine if you're using RAM to store an object, because RAM is Random Acess Memory and is therefore suited to the job.

When you need to store your object on a medium that is not traditionally random access, for instance disk, or you need to transfer an object over a stream medium (such as the network) then the object needs to be converted into a form that is suitable to the relevant medium. This conversion process is called serialization, because the structured object is flattened or serialized, making it more amenable to being stored for the long term, or transferred over the network.

Why not just copy the bits comprising the object in RAM to disk, or send it as an opaque blob over the network? ... you may ask. A few issues:

1. Often the format that the object is stored in memory is proprietary and therefore not suitable for public consumption--the way in which it is stored in memory is optimised for in-memory use.
2. When an object references other objects, those references only have meaning within the context of the running application. It would not be possible to deserialize the object meaningfully unless during the serialization process, the object graph was walked and serialized accordingly. There may be a need to translate those references into a form that has meaning outside the context of an application instance.
3. There may be an interoperability requirement between heterogeneous systems, in which case a standard means of representing the object is required (typically some form of XML is chosen for this).