From: "Ron Wheeler" <rwheeler@xxxxxxxxxxxxxxxxxxxxx>
> The origin of this discussion was a BOM (bill of
> materials) problem which is well known to require a
> multiple inheritance model of arbitrary depth. (01)
"Well known"? Yes, it is, I suppose, "well known": it is
indeed a very common fallacy that BOM involves inheritance,
and whether it's single or multiple is not the issue. One
sees it continually in bad OO teaching in otherwise
respectable quarters, and even in so-called "OO"
environments (where they often call it "interface
inheritance"), that the "contains" relationship is regarded
as mediating inheritance, whereas inheritance is of course a
matter of the "isA" relationship. Fortunately for the
perpetrators, though, their OO is usually so perverted that
nobody seem to notice, or care. (02)
By the way (and I must be getting rather predictable in this
sort of comment...), in the coming "5th instalment" of my
"MACK basics" series you will start seeing some nice
examples of the striking advantages of proper inheritance,
very insistently involving the "isA" relationship, which, as
it happens, is usefully orthogonal to "contains". (03)
Sorry, Ron, to use you in this way, but I hope it is evident
in my comments that you can't really be blamed! (You see, I
can be really liberal and blame your environment...) (04)
Christopher (05)
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