I ran into the same problem. Since my structs are all #:prefab, I copy
them like this:
(define (copy s)
(read (open-input-string (with-output-to-string (lambda () (write s))))))
Probably not the best, but works for me.
Thanks,
Dave
On 11/17/2014 12:25 PM, Sam Tobin-Hochstadt wrote:
Unfortunately, you can't really do this in a general way for structs.
There are a couple possible solutions:
- use objects/classes and implement a `clone` or a `replace` method
- use generics, with a `clone` or `replace` generic function
Sam
On Mon, Nov 17, 2014 at 12:22 PM, Matthew Butterick <m...@mbtype.com> wrote:
This seems rudimentary, but I can't figure it out. `struct-copy` requires you
to specify the id of the struct type, like so:
(define copied-struct (struct-copy struct-type-id instance-of-struct))
The docs for struct-copy say "subtypes can be copied as if they were supertypes, but
the result is an instance of the supertype". [1]
OK, but suppose I want the opposite behavior: I want to make a struct-copying
function that accepts instances of a supertype or subtype, but outputs a struct
that's the same type as the input instance (not the supertype).
Possible? Or not possible with structs, because that's what objects & classes
are for?
[1] http://docs.racket-lang.org/reference/struct-copy.html
____________________
Racket Users list:
http://lists.racket-lang.org/users
____________________
Racket Users list:
http://lists.racket-lang.org/users
____________________
Racket Users list:
http://lists.racket-lang.org/users
