On 2003-11-19T02:22:49-0800, Steve Dekorte wrote: > We'll say that all implement, say, a "respondsTo:" method (that takes a > string argument and returns True or False) and some (but not all) > implement a turnOff method. > > Can we have a type that declares that an object implements respondsTo: > and *may* implement turnOff? If so, how does it prevent the possibility > of a "does not respond to turnOff" error? One way to express what you said here, if I understand you correctly, is to have respondsToTurnOff (a special case of respondsTo:) return a certificate (understood by the type system) that the object will indeed respond to turnOff. The simplest such certificate is an object of the type that does respond to turnOff -- the same object. -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig http://www.thismodernworld.com/ Put something activist here!
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