[flexi-streams-devel] Programmatic classes scrap boilerplate code

[Michael Weber]

Hi Edi,

I looked at flexi-streams' stream.lisp some time ago, and there seems  
to be a lot of boilerplate code to combine various mixins to specific  
stream classes.  Then, there seems to be code for parsing and  
combining what basically amounts to mixin designators, which are then  
again mapped on the specific stream classes.

The underlying issue is not new.  AMOP describes a nice way around it  
which creates classes composed from several mixins programmatically.   
About a year or so ago,  Christophe Rhodes fixed SBCL so that it  
accepts generalized class names.  The support code is little, you can  
find it here (usage example at the end of this mail):
http://www.foldr.org/~michaelw/lisp/amop-programmatic-class.lisp

I can't tell how well this is supported in Lispworks and other  
implementations, but it might be worth opening trouble tickets if  
it's not. :)

OTOH, I understand the cost that comes with maintaining special-cased  
code for non-supporting implementations.  It might not be worth it.

Still, I felt like sharing this, before I forget again. :)


Cheers,
Michael

;;; Example code:
(progn
   (defclass shape () ())
   (defclass circle (shape) ())

   (defclass color () ())
   (defclass orange (color) ())
   (defclass mangenta (color) ())

   (defclass label-type () ())
   (defclass top-labeled (label-type) ())
   (defclass bottom-labeled (label-type) ()))
#||
===> (class-direct-subclasses (find-class 'circle))
()
===> (defparameter *i1* (make-programmatic-instance '(circle orange  
top-labeled)))
===> (defparameter *i2* (make-programmatic-instance '(circle mangenta  
bottom-labeled)))
===> (defparameter *i3* (make-programmatic-instance '(circle orange  
top-labeled)))
===> (class-direct-subclasses (find-class 'circle))
(#<Standard-Class (CIRCLE MAGENTA BOTTOM-LABELED) >
#<Standard-Class (CIRCLE ORANGE TOP-LABELED) >)
||#