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" - D&C 93 > _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
