[racket] struct-copy with sub-types

The phrase "immediate instance of id" is meant to suggest that it
doesn't have the extended fields.

What would you have written?

Robby

On Fri, Mar 25, 2011 at 10:04 AM, Nadeem Abdul Hamid <nadeem at acm.org> wrote:
> In that case, the documentation should probably be updated clearly to
> note this different behavior -- the last sentence of the current:
> http://docs.racket-lang.org/reference/struct-copy.html
> says:
>
> "
> (struct-copy id struct-expr [field-id expr] ...)
> ....
> The result of struct-expr can be an instance of a sub-type of id, but
> the resulting copy is an immediate instance of id (not the sub-type).
> "
>
> Which is why I didn't interpret the behavior as a bug, but a
> limitation (albeit weird) of struct-copy.
>
> --- nadeem
>
>
> On Fri, Mar 25, 2011 at 10:49 AM, Robby Findler
> <robby at eecs.northwestern.edu> wrote:
>> Hi, and sorry for the delay. I've pushed a fix for this, altho it is
>> more like a new feature since the code below still doesn't work--- you
>> have to explicitly name the struct that had the field when it isn't
>> the first argument to struct-copy.
>>
>> Robby
>>
>> On Fri, Mar 25, 2011 at 7:52 AM, Pierpaolo Bernardi <olopierpa at gmail.com> wrote:
>>> On Wed, Mar 23, 2011 at 00:49, Nadeem Abdul Hamid <nadeem at acm.org> wrote:
>>>> Is there anything like struct-copy that works to functionally update a
>>>> field value in a structure, where the field happens to be defined in
>>>> the super-type? In the example below, I want to "functionally update"
>>>> a field of the sub structure inherited from the base definition...
>>>>
>>>>
>>>> (struct base (a b) #:transparent)
>>>> (struct sub base (c) #:transparent)
>>>>
>>>> (define S (sub 1 2 3))
>>>>
>>>> (struct-copy sub S [c 4]) ; works
>>>> ; doesn't work: (struct-copy sub S [b 4])
>>>> (struct-copy base S [b 4]) ; produces a base, not sub
>>>
>>> No answers?
>>>
>>> it looks to me that
>>>
>>> (struct-copy sub S [b 4])
>>>
>>> should work, but it doesn't.  Isn't this a bug?
>>>
>>> If it is not considered a bug, maybe the docs need a clarification?
>>>
>>> Cheers
>>> P.
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>>
>