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
