Is there a way to define a struct so that it has a field whose value is filled in (instead of passed to the constructor) with a value derived from other fields? For example, could you define a struct foo with two explicit fields, x and y, plus a field called z whose value is computed as (+ x y) (yes, simple, but imagine that this is a more expensive operation):
> (define foo1 (foo 1 2)) > (define foo2 (foo 7 12)) > (foo-z foo1) 3 > (foo-z foo2) 19 The closest I could find in the documentation was the #:auto property, but: 1. it makes the field mutable, even though I'm not interested in mutating z 2. the default value is fixed across all constructions, while I want z to depend on x and y Of course, I could make z an explicit field, write a custom constructor, and export that instead of the default constructor for foo. But that seems to be a Royal Pain, especially since (AFAIK) you can't provide the struct as a whole anymore. (And I need to write about 12 of these structs to boot.) -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/9f9e1548-d01d-469f-b565-22601e02dd82n%40googlegroups.com.
