Re: [Sawfish] hash table and concat

[womble@xxxxxxxxx]

On 25/09/11 21:35, fuchur wrote:
> Hi,
> 
> I can't work with hash tables and concat. In sawfish-client i type:
> 
> (require 'rep.data.tables)
> (define test-cache (make-weak-table eq-hash eq))
> (define (cache my-name)
>   (or
>    (table-ref test-cache my-name)
>    (table-set test-cache my-name 'image)))
> 
> (cache 'first-name)
> image
> 
> if i now type:
> (table-ref test-cache 'first-name)
> image
> 
> it's returns image like expected.
> 
> 
> 
> 
> If i use concat like this:
> 
> (require 'rep.data.tables)
> (define test-cache (make-weak-table eq-hash eq))
> (define (cache my-name)
>   (or
>    (table-ref test-cache my-name)
>    (table-set test-cache my-name 'image)))
> 
> (cache (concat "first-" "name"))
> image
> 
> if i now type:
> (table-ref test-cache '"first-name")
> ()
> it's returns ().
> 
> 
> Anyone a idea what is wrong?
> 
> Thank you.
> 

Hi fuchur,

your hash-table is defined with test 'eq, but strings
are not 'eq, only 'equal

(eq "foo" "foo")
()

(equal "foo" "foo")
t

Thus you need to say
   (define test-cache (make-weak-table equal-hash equal))

Note that you need both 'equal-hash' to generate the key,
and 'equal' for comparison. 'eq-hash' uses the address of
the object to generate the key, but two strings of the same
contents nevertheless usually have different addresses in
memory.

Regards,
womble.


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