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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/9f9e1548-d01d-469f-b565-22601e02dd82n%40googlegroups.com.
