Node:Class Redefinition, Next:Method Definition, Previous:Instance Creation, Up:MOP Specification

4.3 Class Redefinition

The default class-redefinition method, specialized for classes with the default metaclass <class>, has the following internal protocol.

[ *fixme* I'm not sure that I understand this sufficiently to explain it. Also, the internals of the default class redefinition method are extremely implementation-specific, and I'm not sure that there is that much point trying to describe the internal protocol such that it could be customized without going to look at the source code. ]

class-redefinition (old <class>) (new <class>) (method)

• remove-class-accessors! old (generic)
• update-direct-method! method old new (generic)
• update-direct-subclass! subclass old new (generic)

The default update-direct-subclass! method invokes class-redefinition recursively to handle the redefinition of the subclass.

When a class is redefined, any existing instance of the redefined class will be modified for the new class definition before the next time that any of the instance's slot is referenced or set. GOOPS modifies each instance by calling the generic function change-class. [ *fixme* Actually it sometimes calls change-class and sometimes change-object-class, and I don't understand why. ]

The default change-class method copies slot values from the old to the modified instance, and initializes new slots, as described in Changing the Class of an Instance. After doing so, it makes a generic function invocation that can be used to customize the instance update algorithm.

change-class (old-instance <object>) (new <class>) (method)

• update-instance-for-different-class old-instance new-instance (generic)

  change-class invokes update-instance-for-different-class as the last thing that it does before returning. The applied method can make any further adjustments to new-instance that are required to complete or modify the change of class. The return value from the applied method is ignored.

  The default update-instance-for-different-class method does nothing.