Awesome! Thank you very much! It does look more elegant than using
method overrides.
On 8/24/2011 4:20 PM, Jon Rafkind wrote:
Here is the code. I had to split the abstract methods from the
concrete methods in the interface. The trick with mixins is that they
can't be instantiated themselves, you have to apply them to some class
and then instantiate that class.
#lang racket
(provide
first-child-class%
second-child-class%)
(define child-interface-partial
(interface ()
child-method
))
(define child-interface
(interface (child-interface-partial)
child-implementation-dependent-method))
#;
(define generic-parent-class%
(class* object% ()
(super-new)
(define/public (child-method this-time) (error 'child-method
"abstract method"))
(define/public (child-implementation-dependent-method
given-inputs-list)
(map
(lambda(this-item)
(eprintf "Next list item is ~v" (child-method this-item)))
given-inputs-list))))
(define generic-parent-class-mixin
(mixin (child-interface-partial)
(child-interface)
(define/public (child-implementation-dependent-method
given-inputs-list)
(map
(lambda(this-item)
(eprintf "Next list item is ~v\n" (send this
child-method this-item)))
given-inputs-list))
(super-new)))
(define first-child-class%
(generic-parent-class-mixin
(class* object% (child-interface-partial)
(super-new)
(define/public (child-method given-input)
(string-append "First got " given-input)))))
(define second-child-class%
(generic-parent-class-mixin
(class* object% (child-interface-partial)
(super-new)
(define/public (child-method given-input)
(string-append "Second got " given-input)))))
(define x1 (new first-child-class%))
(define x2 (new second-child-class%))
(send x1 child-implementation-dependent-method '("a" "b" "c"))
(send x2 child-implementation-dependent-method '("a" "b" "c"))
Output:
Next list item is "First got a"
Next list item is "First got b"
Next list item is "First got c"
'(#<void> #<void> #<void>)
Next list item is "Second got a"
Next list item is "Second got b"
Next list item is "Second got c"
'(#<void> #<void> #<void>)
On 08/24/2011 11:18 AM, Alexander Kasiukov wrote:
Dear Jon,
Thank you very much for your help! I got what I needed to work with
method overrides (following a suggestion of Robby Findler), but it
does look like mixins may give a less redundant way to accomplish the
same functionality. I am at a loss trying to understand how to make
them work based on the Bakus-Naur description. (I am just starting to
learn Racket and Lisp in general.) Could you show an example or
suggest a place where I can look up one? I am trying to do something
along the lines of
#lang racket
(provide
first-child-class%
second-child-class%)
(define child-interface
(interface ()
child-implementation-dependent-method
child-method))
(define generic-parent-class%
(class* object% ()
(super-new)
(define/public (child-method this-time) (error 'child-method
"abstract method"))
(define/public (child-implementation-dependent-method
given-inputs-list)
(map
(lambda(this-item)
(eprintf "Next list item is ~v" (child-method
this-item)))
given-inputs-list))))
(define first-child-class%
(class* generic-parent-class% (child-interface)
(super-new)
(define/override (child-method given-input)
(string-append "First got " given-input))))
(define second-child-class%
(class* generic-parent-class% (child-interface)
(super-new)
(define/override (child-method given-input)
(string-append "Second got " given-input))))
Sincerely yours,
Alex
Date: Wed, 24 Aug 2011 09:04:40 -0600
From: Jon Rafkind<rafk...@cs.utah.edu>
To:users@racket-lang.org
Subject: Re: [racket] How to use abstract classes?
Message-ID:<4e551308.5020...@cs.utah.edu>
Content-Type: text/plain; charset=ISO-8859-1
You could use a
mixin.http://docs.racket-lang.org/reference/mixins.html?q=mixin&q=class#(form._((lib._racket/private/class-internal..rkt)._mixin))
On 08/24/2011 08:31 AM, Alexander Kasiukov wrote:
Dear Racket users,
What is the best way to make a class in Racket abstract? I would like to have a
class which
never gets instantiated
implements certain methods common to all of its children
needs to call some of the methods implemented in the children.
Sincerely yours,
Alex
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