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 <[email protected]> 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 <[email protected]> > wrote: >> On Wed, Mar 23, 2011 at 00:49, Nadeem Abdul Hamid <[email protected]> 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. >> _________________________________________________ >> For list-related administrative tasks: >> http://lists.racket-lang.org/listinfo/users >> > _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
