On Mon, 30 Dec 2013 15:40:08 -0600 Robby Findler <ro...@eecs.northwestern.edu> wrote:
> The hash tables seem fine to me, but maybe we need a better example. > > #lang racket > > (struct cpd (x y)) > > (define C1 (cpd 1 "bla")) > (define C2 (cpd 1 "bla")) > > (equal? C1 C2) > #f > > (define ht (make-hash)) > (hash-set! ht C1 1) > (hash-set! ht C2 2) > (equal? (hash-ref ht C1) > (hash-ref ht C2)) > ;; produces #f > > Actually, it is all fine. In my real code I had used #:transparent and the hash table code worked as expected. Then when reading that make-hash uses equal? I wasn't sure how equal? does work with structs. My small test were without #:transparent, and I didn't realize that exactly this makes the difference. -- Thanks, Manfred > On Sat, Dec 28, 2013 at 5:34 PM, Sam Tobin-Hochstadt > <sa...@cs.indiana.edu>wrote: > > > While your answer is what Manfred is looking for, I still find the > > original behavior worrying. It lets you expose the internals of > > opaque data structures without having the relevant inspector. > > > > Sam > > On Dec 28, 2013 4:16 PM, "J. Ian Johnson" > > <i...@ccs.neu.edu> wrote: > > > >> You want to make sure your structs are inspectable. You can define > >> your structs with the #:transparent option or define your own > >> equality relation with the gen:equal+hash generic interface. > >> -Ian > >> ----- Original Message ----- > >> From: Manfred Lotz <manfred.l...@arcor.de> > >> To: users@racket-lang.org > >> Sent: Sat, 28 Dec 2013 15:41:28 -0500 (EST) > >> Subject: [racket] hash table confusion > >> > >> I have a hash table (created by using make-hash) where the key is a > >> struct. This seems to work fine although the documentation says > >> The make-hash procedure creates a table where keys are compared > >> with equal?,... > >> > >> and it seems that equal? gives #f if I compare two structs having > >> the same contents: > >> > >> > >> (struct cpd (x y)) > >> > >> (define C1 (cpd 1 "bla")) > >> (define C2 (cpd 1 "bla")) > >> > >> (equal? C1 C2) > >> #f > >> > >> > >> Why does my hash table work fine? In my hash handling I'm using > >> make-hash, hash-ref!, hash-set!, hash-for-each. > >> > >> -- > >> Manfred > >> > >> > >> ____________________ > >> Racket Users list: > >> http://lists.racket-lang.org/users > >> > >> ____________________ > >> Racket Users list: > >> http://lists.racket-lang.org/users > >> > > > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > > > > > ____________________ Racket Users list: http://lists.racket-lang.org/users
