[racket] hash table confusion

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


On Sat, Dec 28, 2013 at 5:34 PM, Sam Tobin-Hochstadt
<samth at 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" <ianj at 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.lotz at arcor.de>
>> To: users at 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
>>
>>
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