This is Andreas Hiltner and Mark Grinnell going over how you approach a migration from OST classic to ObjectStudio 8. Some limitations:

• ObjectStudio allows "- 500" as a message - that's not supported
• For backwards compatibility, method parameters can be overwritten. VW typically does not allow that.
• Global Variables are now SharedVariables defined in the ObjectStudio namespace.
• The ObjectStudio 8 compiler does not allow duplicate names between instance and class instance variables
• Immutability: literals cannot be changed at runtime (however note: in the Parcels directory, there's a backwards compatibility parcel).
• All loaded ObjectStudio code will end up in the ObjectStudio namespace (and, you need to descend from those classes in order to get the ObjectStudio Smalltalk compiler)
• If you subclass collections, you need to implement the instance method #copyEmpty: in order to copy any new instance variables you want to preserve.
• Note the #at: and #at:put: have different return semantics between OS and VW. The OS semantics have been preserved in the OS8 classes.
• Note that #whileTrue: now returns nil, and #whileFalse: also returns nil. In classic OS, they had returned true and false (respectively)
• The new Date class only allows valid dates (it raises an exception on errors). Also, month names are now case sensitive.
• Processes: Classic OS uses native threads for Smalltalk processes. In OS 8, these are all green threads (eliminates a host of synchronization issues). The ThreadBrowser has been replaced by the ProcessMonitor.
• SendHooks don't exist - MethodWrappers are the VW version of that.
• Breakpoints do not have much overhead any longer.
• User written primitives: you may well have to make some modifications to these - we provide an example makefile showing what you need to do.
• Nil (with the capital) is now a special instance of OPTR. Any pointer should be checked against Nil, not NULL or 0 (zero)
• SQL Server: The old db-lib interface has been deprecated - the interface now uses ODBC.