Classes

A class is a user-defined type that holds a list of fields, just like a struct. Classes also offer capabilities not offered by structs:

• Extensibility
  You can extend a class through inheritance and optional fields

• Graph preservation
  You can transmit a graph of class instances through a Slice operation

• Null/not-set value
  A class parameter or field can be null or not-set, whereas a struct parameter or field must have a value

• Slicing
  A recipient can unmarshal a class instance into a base class by slicing off derived "slices" it does not know

These extra capabilities are not free: the marshaling/unmarshaling of a class is much more complex and time consuming than thethe marshaling/unmarshaling of a struct, and its binary representation is larger. As a result, you should only select a class over a struct when these extra capabilities may be useful for your application.

A class represents data that you transmit over the wire, just like a struct. You can't define operations on a Slice class or implement an interface with a Slice class.