Re: Design By Contract

[jsa@alexandria.organon.com (Jon S Anthony)]

In article <EFnoJv.1vx@syd.csa.com.au> nospam@thanks.com.au (Don Harrison) writes:

> :Isn't that exactly the point?  Why should a client be able to see the
> :actual structure, aka implementation????
> 
> No, the point is that there is no need to hide the structure of an attribute
> so long as it's read-only (look-but-don't-touch). These semantics allow you 
> to query components of visible objects directly:

I'm not convinced that is sufficient.  Knowing the structure can lead
one into writing things that still depend on it (efficiency hacks come
quickly to mind).

> I prefer the Eiffel model because:
> 
>   - It's simple and direct.
>   - It doesn't clutter the spec and body with functions.
>   - It doesn't force you to invent multiple identifiers (one of which has 
>     a contrived name: "the_a" above).

Fine.  Of course, all of these are simply _subjective_
characterizations.  If that is what floats your boat - go for it.

> IMO, the other possibilities for attributes in Ada are unattractive
> because they are either too permissive (look-and-touch - attributes
> declared in the visible part of the spec) or too restrictive
> (don't-look-don't touch - private attributes).

Again, this is simply personal perspective.  It may mean a lot to you,
but you should be aware that this subjective stuff ("unattractive"
"too permissive" "too restrictive") is just opinion and preference and
that others may well view _your_ preferences as "unattractive", "too
permissive" and "too restrictive".  There just is no consistent
objective criteria here.  And no amount of saying it's so will make it
so.

/Jon
-- 
Jon Anthony
OMI, Belmont, MA 02178, 617.484.3383 
"Nightmares - Ha!  The way my life's been going lately,
 Who'd notice?"  -- Londo Mollari