Is it possible to respect the old contract throughout? The extra information can be exposed to the concrete subclasses through private interface.
Sent from my iPhone > On Sep 3, 2015, at 07:44, Graham Cox <graham....@bigpond.com> wrote: > > >> On 3 Sep 2015, at 1:34 am, Maxthon Chan <m...@maxchan.info> wrote: >> >> If this is your use case you can internally call the new method throughout, >> and the new method discards the useless information and calls the old method >> using the old contract. Updated programs will override the new method, >> adopting the new behaviour, while contract of the old override point is >> still respected and old program will still work. >> >> By the way mark your old method as deprecated, as it will generate a warning >> and motivate the users of your library to adopt the new interface faster. > > > This is usually how I handle this sort of thing. However in this case there > are a few additional kinks that made that approach awkward - I > (over)simplified the use case. > > The real case is that the framework itself subclasses GCBase for a couple of > concrete implementations, and client code then typically subclasses one of > these concrete classes (though also sometimes will subclass GCBase itself). > The framework’s own concrete classes need the extra parameter so override the > new version of the method, but the client subclasses override the old method. > So the updated internal subclasses either need to individually consider all > the possible overrides and make sure they’re called, or the underlying base > class can worry about it in one place and detect which one to call, which was > what I was asking about. > > I guess it does make a difference whether this intermediate subclassing takes > place or not, so sorry I oversimplified by leaving it out of the story. > > —Graham > >
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