CLOS Qs
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From: danb on 24 Apr 2008 12:29 Just a couple questions about CLOS: 1. What's the best/most-reliable way to determine whether a value is a clos object, ie. something that may have slots that can be accessed with slot-value? So far, the two possibilities seem to be (subtypep (type-of val) 'standard-object) and (find-class val) 2. How can you tell whether a particular symbol names an accessor for a particular object? --Dan ------------------------------------------------ Dan Bensen http://www.prairienet.org/~dsb/
From: Rainer Joswig on 24 Apr 2008 13:35 In article <9b79cf3a-16fd-406f-bb85-3103bc7e0159(a)z72g2000hsb.googlegroups.com>, danb <sogwaldan(a)gmail.com> wrote: > Just a couple questions about CLOS: > > 1. What's the best/most-reliable way to determine whether > a value is a clos object, ie. something that may have slots that > can be accessed with slot-value? So far, the two possibilities > seem to be > (subtypep (type-of val) 'standard-object) (typep val 'standard-object) ? > and > (find-class val) > > 2. How can you tell whether a particular symbol names > an accessor for a particular object? You can check whether the symbol is a generic function, has one parameter and is applicable with the object as an argument. With the MOP you could check whether the applicable method is of the class STANDARD-READER-METHOD . > > --Dan > > ------------------------------------------------ > Dan Bensen > http://www.prairienet.org/~dsb/ -- http://lispm.dyndns.org/
From: Thomas A. Russ on 24 Apr 2008 13:59 danb <sogwaldan(a)gmail.com> writes: > Just a couple questions about CLOS: > > 1. What's the best/most-reliable way to determine whether > a value is a clos object, ie. something that may have slots that > can be accessed with slot-value? So far, the two possibilities > seem to be > (subtypep (type-of val) 'standard-object) > and > (find-class val) (typep val 'standard-object) is perhaps simpler still. > 2. How can you tell whether a particular symbol names > an accessor for a particular object? You would have to use some of the MOP functions to do this. For example: (mop:finalize-inheritance (find-class 'class-name)) (mapcar #'mop:slot-definition-readers (mop:class-slots (find-class 'class-name))) will give you a list of the symbols naming slot reader functions for the class in question. You might also need to check mop:slot-definition-writers and possibly parse the (SETF SLOTNAME) forms that returns if you really want accessors and not specifically readers and writers. You will presumably also need to figure out what package corresponds to MOP in your particular implementation as well. -- Thomas A. Russ, USC/Information Sciences Institute
From: Pascal Costanza on 24 Apr 2008 15:42 danb wrote: > Just a couple questions about CLOS: > > 1. What's the best/most-reliable way to determine whether > a value is a clos object, ie. something that may have slots that > can be accessed with slot-value? So far, the two possibilities > seem to be > (subtypep (type-of val) 'standard-object) > and > (find-class val) Others have mentioned (typep val 'standard-object), but (typep (class-of val) 'standard-class) should be even more reliable (but for most practical cases, they are equivalent). > 2. How can you tell whether a particular symbol names > an accessor for a particular object? You can't because symbols don't name accessors. Symbols can name generic functions, and some of the methods associated with a generic function can be accessor methods, but accessor methods themselves are anonymous. What you say you want could be expressed as follows (provided you can use the CLOS MOP): (loop for method in (generic-function-methods (fdefinition fname)) thereis (subtypep method 'standard-accessor-method)) ....but I doubt that this is what you really want... What problem are you actually trying to solve? Pascal -- 1st European Lisp Symposium (ELS'08) http://prog.vub.ac.be/~pcostanza/els08/ My website: http://p-cos.net Common Lisp Document Repository: http://cdr.eurolisp.org Closer to MOP & ContextL: http://common-lisp.net/project/closer/
From: danb on 24 Apr 2008 17:06
On Apr 24, 2:42 pm, Pascal Costanza <p...(a)p-cos.net> wrote: > Others have mentioned (typep val 'standard-object), > but (typep (class-of val) 'standard-class) should be > even more reliable (but for most practical cases, > they are equivalent). Thanks. > > 2. How can you tell whether a particular symbol names > > an accessor for a particular object? > > You can't because symbols don't name accessors. > Symbols can name generic functions I mean indirectly, given the type of the object. > What you say you want could be expressed as follows > (provided you can use the CLOS MOP): > (loop for method in > (generic-function-methods (fdefinition fname)) > thereis (subtypep method 'standard-accessor-method)) > ...but I doubt that this is what you really want... Maybe not. We'll see. > What problem are you actually trying to solve? I'm trying to generate code that matches a value against a pattern that's looking for a clos object with certain accessors. There's a man page here: http://www.prairienet.org/~dsb/clmatch-api.htm#accsrs Thanks for the help, Pascal. --Dan ------------------------------------------------ Dan Bensen http://www.prairienet.org/~dsb/ |