Re: Redefine to make a contract stronger (Was: is_equal ofHASHABLE)

Frank Boehme wrote:
> ... I have a general relation class (lets call it R) and a number
> of more specified ones that inherit from R (conforming). These are
> REFL_R (reflexive relations), IRR_R (irreflexive), SYM_R (symmetric),
> ANTSYM_R (antisymmetric) and TRANS_R (transive relations) to name but a
> few. All these classes do not change anything but adding postconditions
> to already existing features from R which provide concatanation,
> reversion etc. Of course, it is very common to inherit from more than
> one of these ... I do not want to have any of these
> classes deferred ...
> Now, it might be a little counterintuitive to have something like
> 
> class LESS_THAN
> inherit
>   IRR_R undefine .... end
>   ANTSYM_R undefine .... end
>   TRANS_R
> ...
> 
> It does not matter which of the parents has no 'undefine' but there must
> be exactly one. A little odd, given the fact that LESS_THAN *is*
> irreflexive, antisymmetric and transitive and all of these three
> properties are equally significant.

You could presumably keep the symmetry by doing it like this:
   class LESS_THAN
   inherit
      IRR_R undefine .... end      -- property
      ANTSYM_R undefine .... end   -- property
      TRANS_R undefine .... end    -- property
      R                            -- implementation
...

> No no, I strongly advocate the new keyword 'recontract'! We do need
> this! :-))

A better keyword might be "renegotiate"?

Regards,
-- 
Roger Browne <[email protected]>