On Wed, 2010-12-29 at 13:42 -0700, Matthew Flatt wrote: > At Wed, 29 Dec 2010 19:23:24 +0200, Markku Rontu wrote: > > Now what would be closer to my wishes is something like this where the > > counter is protected and not exposed. > > > > --- > > > > (define protected-counted-trait > > (trait > > (define counter 0) > > > > (define/public (add!) > > (set! counter (add1 counter))) > > > > (define/public (current-count) > > counter))) > > > > --- > > > > This however is not possible as far as I know. There is a hint to some > > solution in the Racket Reference 5.6 Traits: > > > > "External identifiers in trait, trait-exclude, trait-exclude-field, > > trait-alias, trait-rename, and trait-rename-field forms are subject to > > binding via define-member-name and define-local-member-name. Although > > private methods or fields are not allowed in a trait form, they can be > > simulated by using a public or field declaration and a name whose scope > > is limited to the trait form." > > Like this: > > (define protected-counted-trait > (let () > (define-local-member-name counter) > > (trait > (field (counter 0)) > > (define/public (add!) > (set! counter (add1 counter))) > > (define/public (current-count) > counter)))) >
Thanks! That does the trick. I wrote a macro to have a "trait/private" that introduces "field/private" which does the magic behind the scenes. -Markku _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
