Got it. I'm actually relieved that this isn't possible, since it means I wasn't simply being dumb.
On Wed, Mar 25, 2020, 7:41 PM Sam Phillips <samdphill...@gmail.com> wrote: > On 2020-03-25 14:16, David Storrs wrote: > > This would let me use a struct as an output port: > > > > (struct foo (name out) #:property prop:output-port (struct-field-index > out)) > > > > I'd like to be able to set up a struct such that I can use it as a UDP > > socket, something like the following pseudo-code: > > > > (struct foo (socket) #:property prop:udp (struct-field-index socket)) > > > > I see that Racket defines prop:input-port and prop:output-port, but > > there's no prop:udp, nor can I figure out how to do it through the > > structure type properties or generic interfaces. (I feel like I'm > > missing something on those two, so maybe it's just poor understanding.) > > > > Is there a way to do this? > > The way those properties work is that functions that use input-ports and > outputs-ports have knowledge about the properties and check if it is a > struct with those properties. There is no prop:udp though. You could > make one (like the following), but you would need to make your own > wrappers of the existing udp-* functions and have them do the coercion > before passing arguments to the existing racket functions. > > Cheers, > Sam > > --- >8 --- >8 --- > > #lang racket/base > > (require (prefix-in - racket/udp)) > > (define-values (prop:udp prop:udp? udp-socket-ref) > (make-struct-type-property > 'prop:udp > (lambda (val struct-info) > (cond > [(procedure? val) val] > [(exact-nonnegative-integer? val) > ; XXX: check for valid index > (let ([struct-ref (list-ref struct-info 3)]) > (lambda (a-struct-value) > (struct-ref a-struct-value val)))])))) > > (define (->udp-socket v) > (cond > [(-udp? v) v] > [else > (->udp-socket ((udp-socket-ref v) v))])) > > ;; Something like this for every udp function > (define (udp-bind! socket hostname-string port-no [reuse? #f]) > (-udp-bind! (->udp-socket socket) > hostname-string > port-no > reuse?)) > > (struct server (socket) > #:property > prop:udp (struct-field-index socket) > #:transparent) > > (define (make-server) > (let ([udp (-udp-open-socket)]) > (server udp))) > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/racket-users/34622180-8073-1e61-8187-f7d9dc48b236%40gmail.com > . > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAE8gKofUwGm7YexxvLJkMA9gtfRoW_ixr948WNwMShD_0-iA1g%40mail.gmail.com.
