[plt-scheme] Class methods and class fields

I think that inheritance is mismatched to what you want and that kind
of thing only comes about because languages like you mentioned earlier
don't have anything that isn't attached to a class somehow.

For the examples you've described, you really just want lexical scope
(plus a module system), IMO. Even for the code you write below, it
seems to me that you just want to put my-class and my-derived-class
into one module and have db-connection at the top-level of that
module.

Robby

On Tue, Apr 29, 2008 at 8:29 AM, Eddie Sullivan <eddieSull at hotmail.com> wrote:
> That gives some of the functionality, but doesn't specifically associate the
> variable with the class, and doesn't allow for inheritance the way structure
> type properties do. To add to your example, I can envision something like:
>
>
>  (define my-class%
>   (class object%
>    ;; Just initialized once ever:
>    (static-field [db-connection (init-db)])
>
>    (define/public (talk-to-db stuff) ... db-connection ...)
>    (super-new)))
>
>  (define my-derived-class%
>   (class my-class%
>    ;; Provides access to superclass's static field:
>    (inherit-static-field db-connection)
>    (define/public (more-db-talking stuff) ... db-connection ...)
>    (super-new)))
>
>  (let ([dbc (get-static-field db-connection my-derived-class%)])
>   ... dbc ...)
>
>  ----- Original Message ----- From: "Robby Findler" <robby at cs.uchicago.edu>
>  To: "Eddie Sullivan" <eddieSull at hotmail.com>
>  Cc: <plt-scheme at list.cs.brown.edu>
>  Sent: Tuesday, April 29, 2008 8:43 AM
>  Subject: Re: [plt-scheme] Class methods and class fields
>
>
>
>
>
> > The PLT Scheme class system is embedded in an ordinary functional
> > language, so you can just define functions or database connections
> > outside the class an refer to those variables lexically, eg:
> >
> > (define db-connection (init-db))
> > (define my-class%
> >  (class object%
> >   (define/public (talk-to-db stuff) ... db-connection ...)
> >   (super-new)))
> >
> > Robby
> >
> > On Tue, Apr 29, 2008 at 7:38 AM, Eddie Sullivan <eddieSull at hotmail.com>
> wrote:
> >
> > > Hi.
> > >  I'm another long-time programmer trying out scheme. I have been working
> > > with PLT's scheme/class module because I am used to
> > >  the object oriented way of thinking about programming.
> > >
> > >  In every other language I have used that has classes (Python and the
> C++
> > >  family, also [incr tcl] but my memory of that is vague), there is the
> > >  concept of "class variables", that is, variables that are associated
> with
> > >  the class itself rather than with any particular instance, and the
> similar
> > >  concept of "class methods." (They're also often called "static", but
> that
> > >  term can be confusing, IMO.)
> > >
> > >  It's easy to imagine scenarios where these concepts would be very
> useful,
> > > such as a
> > >  shared resource like a database connection, or simply a usage counter.
> > >
> > >  Perhaps I'm misreading the documentation, but I can't find anything
> like
> > > that in scheme/class. Structures have "structure type properties", so
> the
> > > idea must be acknowledged to be useful in theory.
> > >
> > >  Is it there and I'm missing it? If not, is there a simple way to
> implement
> > > this functionality that I haven't figured out? Or is there a
> philosophical
> > > reason why this was considered a bad idea?
> > >
> > >  Thanks!
> > >  -Eddie Sullivan
> > >
> > >
> > >  _________________________________________________
> > >  For list-related administrative tasks:
> > >  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> > >
> > >
> >
> >
>
>