Class: ObsoleteObject

• Inheritance
• Description
• Related information
• Class protocol
  • Signal constants
  • initialization
• Instance protocol
  • message catching
  • required protocol

Inheritance:

   nil
   |
   +--ObsoleteObject

  This class inherits NOTHING - most messages will lead into doesNotUnderstand:

Package:

stx:libboss

Category:

System-BinaryStorage

Version:

rev: 1.20 date: 2009/06/30 13:58:26

user: stefan

file: ObsoleteObject.st directory: libboss

module: stx stc-classLibrary: libboss

Author:

Claus Gittinger

Description:

This class is used for error handling during binary object restoration. 
Whenever an object whose class has changed (i.e. it was stored with a 
different layout/size) is about to be restored, it cannot be made an 
instance of the now existing class.
In this case, the BinaryInputManager will create a dummy class for the 
old (obsolete) object and make the restored object an instance of it. 
This dummy class will be a subclass of ObsoleteObject.
Thus, the restored obsolete object will (at least) provide the data
(i.e. the contents) of the original object - although it will obviously
not be able to implement the original protocol.

After the creation of the obsolete object, a signal will be raised (in 
BinaryInputManager), which can be caught by the application to provide
a replacement class and/or to try some automatic or semi-automatic object 
conversion.
The signal gets the obsolete object and the new class as parameters, so
a handler can extract instance values from the obsolete object and construct a
replacement object from those.

ObsoleteObject itself catches all messages, to avoid any use of the restored
object (in case conversion failed or the signal was ignored).

Read the documentatio on binary object storage for examples & code fragments,
on obsolete object handling and object migration.

Related information:

    BinaryObjectStorage
    BinaryIOManager
    PersistencyManager
    [binary object storage]

Class protocol:

 obsoleteObjectSignal

return the signal raised when a message is sent to an Obsolete
signal.

 initialize

Instance protocol:

 doesNotUnderstand: aMessage

the only thing obsolete objects understand is that they don't understand
anything.

 basicAt: index

this method is required to allow cloning of the object

 basicAt: index put: something

this method is required to allow restore of the object

 basicInspect

this method is required to allow inspection of the object

 basicSize

this method is required to allow restore of the object

 become: index

this method is required to allow cloning of the object

 becomeNil

this method is required to allow restore of the object

 becomeSameAs: index

this method is required to allow cloning of the object

 displayString

return a printed representation of the receiver for displaying.
This method is required to allow inspection of the object.

 inspect

this method is required to allow inspection of the object

 instVarAt: index

this method is required to allow inspection of the object

 instVarAt: index put: something

this method is required to allow restore of the object

 isKindOf: aClass

this method is required to allow restore of the object

 readBinaryContentsFrom: stream manager: manager

this method is required to allow restore of the object

 readBinaryContentsFromData: instvarArray manager: manager

this method is required to allow restore of the object