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
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