Re: Clean Object Class Design -- Circle/Ellipse

On Sat, 4 Aug 2001 15:22:40 -0400, "Bob Badour" <bbadour_at_golden.net> wrote:

>>Is it still true that "any model of inheritance in which type
>>Integer is not considered to be a subtype of type Real
>>can hardly be said to be a good model of reality" ?
>
>Yes. It is still true. All of the operators on Real to yield Real apply
>equally when one substitutes an Integer for the Real operand, and all of the
>operators on Real to yield Integer apply equally when one substitutes an
>Integer for the Real operand.
>
>Integers may have additional operators and properties that do not apply to
>all Reals, which makes Integer a proper subtype of Real.
>
>Quite frankly, I do not think it is Date who misunderstands "type".
>
>
>>To put bluntly, " Type Inheritance: Is a Circle an Ellipse?"
>>documents lack of understanding of types (and OO),
>>and the usefulness of Date's inheritance model approaches zero.
>
>Your statement is not only blunt: It is also an extraordinary statement
>requiring extraordinary proof, which you have failed to provide, and to put
>it bluntly, it is also incorrect.
>

Once again (from my earlier post):
 RA is a field, whereas IA is only a ring and thus does nort preserve all properties of RA (existence of multiplicative inverse in particular).

Is that enough of a proof that IA is not a subtype of RA (though Date would postulate that it is, since I is a subset of R)?

Marc Gluch
Mindtap inc. Received on Sun Aug 05 2001 - 04:36:35 CEST