Re: Composition vs. inheritance
Todd <todd.heidenthal@lmco.com> writes:
Obviously, I am missing something fundamental, so I apologize if I
seem to be going in circles (no pun intended).
When you answer to a post, you should only quote
the parts you directly refer to. Google Groups
is not a good newsreader.
The whole rectangle square discussion only stems
from insufficiant care to distinguish between
value and storage objects.
Let Q be the set of ?quarternary digits? {0,1,2,3},
its subset {0,1} is called B; B is ?the set of
binary digits?. The inclusion
B c Q (B is a subset of Q)
is valid.
A quartary storage q* can store a quartary digit. It
also might be used to store a binary digit. However, one
can not use any binary storage to store any quartenary digit.
So, for the set of binary storages B* and the set of
quartary storages Q*:
Q* c B* (Q* is a subset of B*)
In general, if every B value is a Q value, then every Q storage
is a B storage.
If one now does not care to distinguish between values and
memories, this would be worded as ?If every B is a Q, then
every Q is a B?, which is false.
The rectangle square problem only exists as long as one does
not make it clear whether one wants to model rectangle and
square /values/ or rectangle and square /storages/.