Thank you Pascal for pointing this out, but I don't think this relates to my problem. I have looked at MKCL source and it was evident that it does not implement superclass validation at this time. Its MOP is not supported either in Closer-MOP so I assume it is somewhat young. Quoting for clos/standard.lsp: ;; FIXME!!! Here should come the invocation of VALIDATE-SUPERCLASS! As I have played with various CLs I noted that some required VALIDATE-SUPERCLASS and some did not. I have not really checked what is the standard's stance on this.
I can trace the error rising from defclass to standard.lsp in mkcl. It is the cond clause from ensure-class-using-class. I display some more information to post here. ((not (eq (class-of class) metaclass)) (format *error-output* "class: ~A~%" class) (format *error-output* "(class-of class): ~A~%" (class-of class)) (format *error-output* "metaclass: ~A~%" metaclass) (error "When redefining a class, the metaclass can not change.")))
Which provides this output
class: &<The A-CLASS A 140012460512096> (class-of class): &<The STANDARD-CLASS A-CLASS 140012464325568> metaclass: &<The STANDARD-CLASS A-CLASS 140012460537344> Error during command line arguments processing: When redefining a class, the metaclass can not change..
This does show that A-CLASS is intanciated twice, and it is why the EQ test fails. The mystery is why there happen two instanciations when I use ASDF.
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To: asdf-devel@common-lisp.net From: pjb@informatimago.com Date: Thu, 4 Dec 2014 11:26:50 +0100 Subject: Re: [Asdf-devel] Program with metaclass on MKCL.
"D. Martinez" denis.martinez@live.com writes:
Hello. Being new to "serious" CL programming I am hitting a brick wall right now in one CLOS project. After some time of infructuous searching I cannot find the source of my problem, which may be of either MKCL or ASDF but I lack the knowledge to debug this. Mr. JCB, who I have seen active on this list, may (hopefully!) be able to shed some light on the issue.
The bug I encounter happens when I load the project by the means of ASDF. I can not reproduce it otherwise. It is triggered by a use of a custom metaclass, and it suggests that a file is loaded more times than it should.
I have narrowed down the problem to a small program, so here it is:
;;;; hello.asd (asdf:defsystem &:hello :description "Describe hello here" :author "Your Name your.name@example.com" :license "Specify license here" :serial t :components ((:file "package") (:file "a")) :depends-on ())
;;;; package.lisp (defpackage &:hello (:use &:cl))
;;;; a.lisp (in-package &:hello) (defclass A-class (standard-class) ()) (defclass A (standard-object) () (:metaclass A-class))
AFAIK, you need to define a validate-superclass method when you define a new metaclass:
---- a.lisp ------------------------------------------------------------ (in-package &:hello) (defclass A-class (standard-class) ()) (defmethod validate-superclass ((class A-class) (super standard-class)) t) (defclass A (standard-object) () (:metaclass A-class)) ---- hello.asd --------------------------------------------------------- (asdf:defsystem &:hello :description "Describe hello here" :author "Your Name your.name@example.com" :license "Specify license here" :serial t :components ((:file "package") (:file "a")) :depends-on ("closer-mop")) ---- package.lisp ------------------------------------------------------ (defpackage &:hello (:use &:cl) (:import-from &:closer-mop &:validate-superclass))
I will happily provide more specific info at request. The bug occured on MKCL 1.1.9 and 1.1.10 git with bundled ASDF.
I tested it with ccl.
-- __Pascal Bourguignon__ http://www.informatimago.com/ “The factory of the future will have only two employees, a man and a dog. The man will be there to feed the dog. The dog will be there to keep the man from touching the equipment.” -- Carl Bass CEO Autodesk
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