Ross, This is generally a hard problem in software systems. The only language I know that explicitly addresses it is Erlang. Ultimately you need a system upgrade process, which defines how to update the data in your system to match a new version of the system. You could do this by writing a script that 1) loads the old version of your library 2) loads your data/serialized reference classes 3) exports data to some intermediate format (eg a list) 4) loads new version of library 5) imports data from intermediate format
Once you've gone through the upgrade process, arguably it's better to persist the data in a format that is decoupled from your objects since then future upgrades would simply be 1) load new library 2) import data from intermediate format which is no different from day-to-day operation of your app/system (ie you're always writing to and reading from the intermediate format). Warm regards, Brian â¢â¢â¢â¢â¢ Brian Lee Yung Rowe Founder, Zato Novo Professor, M.S. Data Analytics, CUNY > On Aug 1, 2014, at 1:54 PM, Ross Boylan <r...@biostat.ucsf.edu> wrote: > > I saved objects that were defined using several reference classes. > Later I modified the definition of reference classes a bit, creating new > functions and deleting old ones. The total number of functions did not > change. When I read them back I could only access some of the original > data. > > I asked on the user list and someone suggested sticking with the old > class definitions, creating new classes, reading in the old data, and > converting it to the new classes. This would be awkward (I want the > "new" classes to have the same name as the "old" ones), and I can > probably just leave the old definitions and define the new functions I > need outside of the reference classes. > > Are there any better alternatives? > > On reflection, it's a little surprising that changing the code for a > reference class makes any difference to an existing instance, since all > the function definitions seem to be attached to the instance. One > problem I've had in the past was precisely that redefining a method in a > reference class did not change the behavior of existing instances. So > I've tried to follow the advice to keep the methods light-weight. > > In this case I was trying to move from a show method (that just printed) > to a summary method that returned a summary object. So I wanted to add > a summary method and redefine the show to call summary in the base > class, removing all the subclass definitions of show. > > Regular S4 classes are obviously not as sensitive since they usually > don't include the functions that operate on them, but I suppose if you > changed the slots you'd be in similar trouble. > > Some systems keep track of versions of class definitions and allow one > to write code to migrate old to new forms automatically when the data > are read in. Does R have anything like that? > > The system on which I encountered the problems was running R 2.15. > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel [[alternative HTML version deleted]]
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