bertrand@eiffel.UUCP (Bertrand Meyer) (03/20/89)
Extracted from last message by Roger Rousseau through Kai Ng (complementing earlier comments by Mike Martin, Kai Ng and Chris Genly): > 1. An error in table of page 260 of [OOSC]? > ------------------------------------------- > > This table is not very clear and disturbs my students too. > Moreover, the current implementations (v2.1, at least Sun and Vax/Ultrix) > differ from this table for the last row (#6): in the first column (a1.1), > we observe PHI', not PHI''. > So, is it an error of the book or of the implementations? > > Consequently, I believe: > - the table page 260 of The book is correct, > - the current implementation is erroneous, > - the explanation p 261 about case #6 is not clear. > > In my opinion, case #6 is useful for the rare cases (currently not used in > standard library, maybe that explains the bug wasn't found), where we need > a1.f (the view from a) to differ from b1.f (the view from b), e.g. for > performance considerations. The fact that "b1.f" is an alias of a1.f" > is useful to get access, in B, to the implementation of the view from A > (not the original version PHI, as mentioned on p. 261). > > Can Bertrand confirm or deny all that? This is just a ``non-message'' message, to state that I haven't had time to look carefully at this problem since the original postings, and probably won't be able to do so for at least one more week - but that it does not mean I am ignoring the problems raised by the correspondents listed above. My initial guess is that Mr. Rousseau (as quoted above) is right on all three counts, but I need to spend some time on this. If he is indeed right the implementation will be corrected and the explanation on p. 261 will be improved for the next edition. As case #6 is seldom useful (not just in the basic library) I hope the earth will continue to spin in the meantime. I will contribute a ``real'' answer as soon as I can. -- Bertrand Meyer bertrand@eiffel.com