[plt-scheme] Class methods and class fields

Yes, that sounds about right to me.

Robby

On Tue, Apr 29, 2008 at 10:09 AM, Eddie Sullivan <eddieSull at hotmail.com> wrote:
> I think I see what you're saying: that module variables can accomplish what
> class variables would be used for in other languages, by putting the
> class(es) in its/their own module, or even replacing each class with an
> equivalent module. To take it further, a sort-of inheritance can be
> accomplished by re-providing items from a "parent" module (or is that taking
> the analogy too far?).
>
>  I guess the mental barrier is seeing modules as more than just a way to
> organize source or object code (sort of like C include-files or .NET
> assemblies), but as an intrinsic part of the language at the same level as
> classes and structures.  That and overcoming the C-based aversion to what
> seem like global variables.
>
>  Thanks again, and let me know if I've misunderstood you.
>  -Eddie
>
>
>  ----- 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 9:31 AM
>
>
>  Subject: Re: [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
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> > >
> >
> >
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