dynamic-mixins
dynamic-mixins copied to clipboard
Simple, dynamic class combination for CLOS.
dynamic-mixins
Dynamic-mixins is for simple, dynamic class combination:
(in-package :dynamic-mixins)
(defclass a () ())
(defclass b () ())
(defclass c () ())
(make-instance (mix 'a 'b)) ;; => #<MIXIN-OBJECT (A B)>
(let ((a (make-instance 'a)))
(ensure-mix a 'b 'c) ;; => #<MIXIN-OBJECT (B C A)>
(delete-from-mix a 'a) ;; => #<MIXIN-OBJECT (B C)>
(delete-from-mix a 'c)) ;; => #<B>
This allows objects to be mixed and updated without manually defining many permutations.
Dictionary
-
MIX &rest classes
: This produces a "mix list", which is generally only useful for passing toMAKE-INSTANCE
. Note: Order matters! This determines class precedence. -
ENSURE-MIX object &rest name-or-class
: Ensure that classes listed inname-or-class
are part ofobject
. This will create a new class andCHANGE-CLASS object
if necessary. Note: Order matters! This determines class precedence. -
DELETE-FROM-MIX object &rest name-or-class
: Remove classes listed inname-or-class
from the object's class. This will create a new class andCHANGE-CLASS object
if necessary. However,object
must be aMIXIN-OBJECT
created by(MAKE-INSTANCE (MIX ...) ...)
orENSURE-MIX
. Otherwise, nothing will be changed.
Notes
Order and Precedence
Order matters; you are defining a new class which has the specified classes as direct superclasses.
ENSURE-MIX
prepends classes in the order specified. (Originally,
it appended classes.) This is simply more useful in practice:
(defclass general-object () ())
(defclass specializing-mixin () ())
(defgeneric some-operation (x))
(defmethod some-operation (x)
"Handle the general case"
...)
(defmethod some-operation ((x specializing-mixin))
"Handle the case for SPECIALIZING-MIXIN"
...)
(let ((x (make-instance 'general-object)))
(ensure-mix x 'specializing-mixin)
(some-operation x))
If SPECIALIZING-MIXIN
were appended, the method which specialized on
it would never be called. In practice, this defeats the point.
Therefore, mixins now get precedence.
Errors
Errors regarding precendence and circularity are now handled, or rather, causing such an error will not produce a nearly-unrecoverable situation. Now you will just get an error.