git clone 'https://github.com/rpav/dynamic-mixins.git'
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.
MIX &rest classes: This produces a “mix
list”, which is generally only useful for passing to
MAKE-INSTANCE. Note: Order matters! This determines class
ENSURE-MIX object &rest name-or-class: Ensure that classes listed
name-or-class are part of
object. This will create a new
CHANGE-CLASS object if necessary. Note: Order matters!
This determines class precedence.
DELETE-FROM-MIX object &rest name-or-class: Remove classes listed
name-or-class from the object's class. This will create a new
CHANGE-CLASS object if necessary. However,
must be a
MIXIN-OBJECT created by
(MAKE-INSTANCE (MIX ...) ...)
ENSURE-MIX. Otherwise, nothing will be changed.
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))
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 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.