Re: GOOPS questions

[Marius Vollmer <mvo at zagadka dot ping dot de>]

niko@iris.ica3.uni-stuttgart.de (Niko Neuss) writes:

> Hello, all of you.
> 
> Recently I've started to use GOOPS, and it works quite fine (I also
> switched from my old SGI to a Powerbook with LINUXPPC, and things work
> much smoother now).  It is astonishing how much nicer things can be
> formulated using OO style, and Guile is much more fun now.

Yes, I agree.  Goops is really great.

> 1) I have defined an object to administrate a list of data fields.  The
>    basic class looks as follows:
> 
> (define-class <container> ()
>   (sizes #:accessor my-sizes #:init-keyword #:sizes)
>   (allocs #:accessor my-allocs #:init-keyword #:allocs))
> 
> I would like to have an initialization of this object which looks
> like:

You can do this by defining a method on the "initialize" generic
function.  This is somewhat like defining a constructor in C++, if you
allow me that comparison.

    (define-method initialize ((c <container>) args)
      ;; first initializes the instance from the args
      (next-method)
      ;; and then tweak it into shape
      (set! (my-allocs c) (make-list (length (my-sizes c)) 0)))

[BTW, anyone knows why next-method doesn't take arguments?]

After that,

    (define x (make <container> #:sizes '(10 5)))

will behave as you want it to.

> 3) And finally: why doesn't one use the simpler notation ":accessor",
> ... (as in CLOS) instead of "#:accessor", ...?

You can use the simpler notation after doing

    (read-set! keywords 'prefix)

at the top-level. 

This is actually a `reader' issue and has nothing to do with GOOPS.
It's a question of how keywords are recognized in the source code.
The form `#:keyword' is always recognized as a keyword, while
`:keyword' is normally interpreted as a symbol.  This is because
`:keyword' is a legal R5RS symbol and we didn't want to deviate from
the standard in this regard.  But you can switch back to the more
convenient form, so this is not a great loss.  However, I think we
should have a more, ahem, disciplined way of controlling the
syntax-variants that the Guile reader accepts.  I think the timing of
read-set! with respect to compilation, etc is not well defined.
 
> P.S.: My mail server in Heidelberg is blocked by ORBS and therefore
> also by MAILER-DAEMON@sourceware.cygnus.com.  Please reply to
> <Nicolas.Neuss@IWR.Uni-Heidelberg.De>.  I hope my sysadmins will fix
> the problem soon.

You could also force your From: header in the mean-time or set a
Reply-To: header.

- Marius

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