Re: [racket-dev] [racket] Question about fields in Racket OO
On Thu, Dec 16, 2010 at 12:22 AM, Mark Engelberg mark.engelb...@gmail.com wrote: OK, it works when the set! occurs after the super-new. I didn't think set! would work at all in a class definition (as opposed to within a method); I was thinking of the whole system of defining classes as more of a declarative DSL that only allowed certain constructs. You've probably already figured this out, but the body of a class is a series of definitions and expressions like at the top-level but 'define' taking on the meaning of 'make a field', and a bunch of new definitions appearing. The new stuff says what the methods are, but everything else is just executed in sequence as if it were in the body of the initializer (if this were in Java, say). hth, Robby _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] [racket] Question about fields in Racket OO
Does 'define' really mean 'make a field'? I thought fields had to be specially designated so that get-field would know about them... Yes, this program errors: #lang racket (define c% (class* object% () (field [x 1]) (define y 2) (super-new))) (define o (new c%)) (field-names o) (get-field x o) (get-field y o) -- I agree that 'define' is like making a field, but fields are something special too. Jay On Thu, Dec 16, 2010 at 6:51 AM, Robby Findler ro...@eecs.northwestern.eduwrote: On Thu, Dec 16, 2010 at 12:22 AM, Mark Engelberg mark.engelb...@gmail.com wrote: OK, it works when the set! occurs after the super-new. I didn't think set! would work at all in a class definition (as opposed to within a method); I was thinking of the whole system of defining classes as more of a declarative DSL that only allowed certain constructs. You've probably already figured this out, but the body of a class is a series of definitions and expressions like at the top-level but 'define' taking on the meaning of 'make a field', and a bunch of new definitions appearing. The new stuff says what the methods are, but everything else is just executed in sequence as if it were in the body of the initializer (if this were in Java, say). hth, Robby _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev -- Jay McCarthy j...@cs.byu.edu Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay The glory of God is Intelligence - DC 93 _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] [racket] Question about fields in Racket OO
Yes, sorry -- define is for private fields, not public ones. (This is something that can easily trip people up, ie making fields when they really want to be making methods; but I don't have a good idea of how to fix it.) Robby On Thu, Dec 16, 2010 at 7:56 AM, Jay McCarthy jay.mccar...@gmail.com wrote: Does 'define' really mean 'make a field'? I thought fields had to be specially designated so that get-field would know about them... Yes, this program errors: #lang racket (define c% (class* object% () (field [x 1]) (define y 2) (super-new))) (define o (new c%)) (field-names o) (get-field x o) (get-field y o) -- I agree that 'define' is like making a field, but fields are something special too. Jay On Thu, Dec 16, 2010 at 6:51 AM, Robby Findler ro...@eecs.northwestern.edu wrote: On Thu, Dec 16, 2010 at 12:22 AM, Mark Engelberg mark.engelb...@gmail.com wrote: OK, it works when the set! occurs after the super-new. I didn't think set! would work at all in a class definition (as opposed to within a method); I was thinking of the whole system of defining classes as more of a declarative DSL that only allowed certain constructs. You've probably already figured this out, but the body of a class is a series of definitions and expressions like at the top-level but 'define' taking on the meaning of 'make a field', and a bunch of new definitions appearing. The new stuff says what the methods are, but everything else is just executed in sequence as if it were in the body of the initializer (if this were in Java, say). hth, Robby _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev -- Jay McCarthy j...@cs.byu.edu Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay The glory of God is Intelligence - DC 93 _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] [racket] Question about fields in Racket OO
This seems like a trivial point because the class system doesn't have to track these things and they are in fact part of the closures of the methods, so I don't see in what sense they are fields. Perhaps I am blinded by my reading of the implementation. I certainly agree they are essentially fields, but I can't but think of them as closed-over variables. Jay On Thu, Dec 16, 2010 at 7:00 AM, Carl Eastlund c...@ccs.neu.edu wrote: To quote the class* documentation: ( http://docs.racket-lang.org/reference/createclass.html#%28part._clfields%29 ) Each field, init-field, and non-method define-values clause in a class declares one or more new fields for the class. Fields declared with field or init-field are public. So only the public ones are accessible via get-field. Carl Eastlund On Thu, Dec 16, 2010 at 8:56 AM, Jay McCarthy jay.mccar...@gmail.com wrote: Does 'define' really mean 'make a field'? I thought fields had to be specially designated so that get-field would know about them... Yes, this program errors: #lang racket (define c% (class* object% () (field [x 1]) (define y 2) (super-new))) (define o (new c%)) (field-names o) (get-field x o) (get-field y o) -- I agree that 'define' is like making a field, but fields are something special too. Jay On Thu, Dec 16, 2010 at 6:51 AM, Robby Findler ro...@eecs.northwestern.edu wrote: On Thu, Dec 16, 2010 at 12:22 AM, Mark Engelberg mark.engelb...@gmail.com wrote: OK, it works when the set! occurs after the super-new. I didn't think set! would work at all in a class definition (as opposed to within a method); I was thinking of the whole system of defining classes as more of a declarative DSL that only allowed certain constructs. You've probably already figured this out, but the body of a class is a series of definitions and expressions like at the top-level but 'define' taking on the meaning of 'make a field', and a bunch of new definitions appearing. The new stuff says what the methods are, but everything else is just executed in sequence as if it were in the body of the initializer (if this were in Java, say). hth, Robby -- Jay McCarthy j...@cs.byu.edu Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay The glory of God is Intelligence - DC 93 _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] [racket] Question about fields in Racket OO
There is one field per object, but one method (closure) per class. Otherwise, you're right; and that's just what fields are. :) Robby On Thu, Dec 16, 2010 at 8:08 AM, Jay McCarthy jay.mccar...@gmail.com wrote: This seems like a trivial point because the class system doesn't have to track these things and they are in fact part of the closures of the methods, so I don't see in what sense they are fields. Perhaps I am blinded by my reading of the implementation. I certainly agree they are essentially fields, but I can't but think of them as closed-over variables. Jay On Thu, Dec 16, 2010 at 7:00 AM, Carl Eastlund c...@ccs.neu.edu wrote: To quote the class* documentation: (http://docs.racket-lang.org/reference/createclass.html#%28part._clfields%29) Each field, init-field, and non-method define-values clause in a class declares one or more new fields for the class. Fields declared with field or init-field are public. So only the public ones are accessible via get-field. Carl Eastlund On Thu, Dec 16, 2010 at 8:56 AM, Jay McCarthy jay.mccar...@gmail.com wrote: Does 'define' really mean 'make a field'? I thought fields had to be specially designated so that get-field would know about them... Yes, this program errors: #lang racket (define c% (class* object% () (field [x 1]) (define y 2) (super-new))) (define o (new c%)) (field-names o) (get-field x o) (get-field y o) -- I agree that 'define' is like making a field, but fields are something special too. Jay On Thu, Dec 16, 2010 at 6:51 AM, Robby Findler ro...@eecs.northwestern.edu wrote: On Thu, Dec 16, 2010 at 12:22 AM, Mark Engelberg mark.engelb...@gmail.com wrote: OK, it works when the set! occurs after the super-new. I didn't think set! would work at all in a class definition (as opposed to within a method); I was thinking of the whole system of defining classes as more of a declarative DSL that only allowed certain constructs. You've probably already figured this out, but the body of a class is a series of definitions and expressions like at the top-level but 'define' taking on the meaning of 'make a field', and a bunch of new definitions appearing. The new stuff says what the methods are, but everything else is just executed in sequence as if it were in the body of the initializer (if this were in Java, say). hth, Robby -- Jay McCarthy j...@cs.byu.edu Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay The glory of God is Intelligence - DC 93 _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] [racket] Question about fields in Racket OO
OK, it works when the set! occurs after the super-new. I didn't think set! would work at all in a class definition (as opposed to within a method); I was thinking of the whole system of defining classes as more of a declarative DSL that only allowed certain constructs. Now that you point it out though, I see there is an example in the guide that does set! on an inherited field. Thanks, Mark On Wed, Dec 15, 2010 at 9:53 PM, Robby Findler ro...@eecs.northwestern.eduwrote: set!? Try it in both positions (the commented out one and the other one): the thing to keep in mind is that the declaration in c% is also kind of like a set! that happens when the object is initialized. Robby #lang racket (define c% (class object% (field [f 1]) (define/public (get-f) f) (super-new))) (define d% (class c% (inherit-field f) (set! f 2) (super-new) ; (set! f 2) )) (send (new d%) get-f) On Wed, Dec 15, 2010 at 11:46 PM, Mark Engelberg mark.engelb...@gmail.com wrote: Thanks. That seems to address the shared private issue. So is there a way to give a new value to an inherited field? --Mark On Wed, Dec 15, 2010 at 9:13 PM, Robby Findler ro...@eecs.northwestern.edu wrote: See define-local-member-name. Robby On Wed, Dec 15, 2010 at 10:38 PM, Mark Engelberg mark.engelb...@gmail.com wrote: I'm playing around with the object-oriented subset of Racket, and have a couple of questions. Ideally, I'd like to equip a class with a field that is visible only to it and its subclasses. As far as I can tell, though, this isn't possible. It seems that I have to make a choice between a completely private field visible only to the class (by just using define) or making a completely public field (by using field). Correct? Now, let's say I make the field public. In the subclass, how do I change the default value of field? For example, in the superclass, I might have (field [a 300]) but in the subclass, I want to do something like (inherit-field [a 200]) However, as far as I can tell, the syntax doesn't support anything other than (inherit-field a) Thanks, Mark _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] [racket] Question about fields in Racket OO
set!? Try it in both positions (the commented out one and the other one): the thing to keep in mind is that the declaration in c% is also kind of like a set! that happens when the object is initialized. Robby #lang racket (define c% (class object% (field [f 1]) (define/public (get-f) f) (super-new))) (define d% (class c% (inherit-field f) (set! f 2) (super-new) ; (set! f 2) )) (send (new d%) get-f) On Wed, Dec 15, 2010 at 11:46 PM, Mark Engelberg mark.engelb...@gmail.com wrote: Thanks. That seems to address the shared private issue. So is there a way to give a new value to an inherited field? --Mark On Wed, Dec 15, 2010 at 9:13 PM, Robby Findler ro...@eecs.northwestern.edu wrote: See define-local-member-name. Robby On Wed, Dec 15, 2010 at 10:38 PM, Mark Engelberg mark.engelb...@gmail.com wrote: I'm playing around with the object-oriented subset of Racket, and have a couple of questions. Ideally, I'd like to equip a class with a field that is visible only to it and its subclasses. As far as I can tell, though, this isn't possible. It seems that I have to make a choice between a completely private field visible only to the class (by just using define) or making a completely public field (by using field). Correct? Now, let's say I make the field public. In the subclass, how do I change the default value of field? For example, in the superclass, I might have (field [a 300]) but in the subclass, I want to do something like (inherit-field [a 200]) However, as far as I can tell, the syntax doesn't support anything other than (inherit-field a) Thanks, Mark _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
