+;;;--------------------------------------------------------------------------
+;;; Copying instances.
+
+(export 'copy-instance-using-class)
+(defgeneric copy-instance-using-class (class object &rest initargs)
+ (:documentation
+ "Does the donkey-work behind copy-instance."))
+
+(defmethod copy-instance-using-class
+ ((class standard-class) object &rest initargs)
+ (let ((new (apply #'allocate-instance class initargs)))
+ (dolist (slot (class-slots class))
+ (setf (slot-value-using-class class new slot)
+ (slot-value-using-class class object slot)))
+ (apply #'shared-initialize new nil initargs)
+ new))
+
+(export 'copy-instance)
+(defun copy-instance (object &rest initargs)
+ "Make a copy of OBJECT, modifying it by setting slots as requested by
+ INITARGS."
+ (apply #'copy-instance-using-class (class-of object) object initargs))
+
+;;;--------------------------------------------------------------------------
+;;; Handy macros.
+
+(export 'with-slot-variables)
+(defmacro with-slot-variables (slots instance &body body)
+ "A copy-out-and-write-back variant of with-slots.
+
+ The SLOTS argument is a list of slot specifications, each of which has the
+ form (NAME &key :update :variable). VARIABLE defaults to NAME, and
+ :update defaults to nil.
+
+ The INSTANCE argument has the form (INSTANCE &key :class), but an atom may
+ be used in place of a singleton list. If the CLASS is specified, then two
+ good things happen: firstly the INSTANCE is declared to be a member of the
+ CLASS, and secondly all the slot variables are declared to have the
+ appropriate types, as dredged up from the class's effective slot
+ definitions.
+
+ The effect of all this is to return the result of evaluating BODY in an
+ environment where the VARIABLEs are bound to the values of the NAMEd slots
+ of the given INSTANCE. If BODY completes successfully (rather than
+ throwing out, restarting, or anything like that) then the final values of
+ VARIABLEs for which UPDATE was set non-nil are written back to their
+ corresponding slots.
+
+ This stands a good chance of being rather faster than with-slots. It
+ does, however, run the risk of leaving things in an inconsistent state if
+ BODY escapes half-way through. Also, this requires recompilation if a
+ class's slots change type."
+ (multiple-value-bind (instance class)
+ (destructuring-bind
+ (instance &key class)
+ (listify instance)
+ (values instance (and class (find-class class))))
+ (let ((slots (mapcar (lambda (slot)
+ (destructuring-bind
+ (name &key update (variable name))
+ (listify slot)
+ (list name variable update)))
+ (if slots
+ (listify slots)
+ (mapcar #'slot-definition-name
+ (class-slots class))))))
+ (with-parsed-body (body decls) body
+ (with-gensyms (instvar)
+ `(let ((,instvar ,instance))
+ ,@(and class `((declare (type ,(class-name class) ,instvar))))
+ (let ,(loop for (name var update) in slots
+ collect `(,var (slot-value ,instvar ',name)))
+ ,@(and class
+ `((declare
+ ,@(loop
+ for (name var update) in slots
+ for slot = (or (find name
+ (class-slots class)
+ :key #'slot-definition-name)
+ (error
+ "Slot ~S not found in class ~S."
+ name (class-name class)))
+ collect `(type
+ ,(slot-definition-type slot)
+ ,name)))))
+ ,@decls
+ (multiple-value-prog1
+ (progn ,@body)
+ ,@(loop for (name var update) in slots
+ when update
+ collect `(setf (slot-value ,instvar ',name)
+ ,var))))))))))
+
~mdw / lisp / blobdiff