Ok, yes, on second thought, I guess it is fine. With your fix, (struct-copy sub (sub 1 2 3) [c 4]) ==> (sub 1 2 4) (struct-copy sub (sub 1 2 3) [b 4]) ==> (sub 1 4 3) (struct-copy base (sub 1 2 3) [b 4]) ===> (base 1 4)
is that right? So that sentence applies to the third situation. I guess when the second one didn't work, I assumed somehow that "id" could only be the struct type where the field was actually defined. So it was a bug. Sorry for the confusion, --- nadeem On Fri, Mar 25, 2011 at 11:08 AM, Robby Findler <[email protected]> wrote: > 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 <[email protected]> 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 >> <[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
