Why is contract-out struct immutable?

Questions & Answers
1

It seems struct in contract-out does not support the #:mutable option. Why is that? This is especially strange as struct/contract does support it.

This is regrettable, as changing one into the other is super-tedious. I generally wish there was a bit of advice that would tell me which one to use.

2

It's not? The contract-out struct form automatically detects mutable fields and provides the setter functions with contracts based on the ones for those fields:

#lang racket

(module demo racket
  (provide (contract-out (struct foo ([a string?]))))
  (struct foo ([a #:mutable]) #:transparent))

(require 'demo)

(define x (foo "bar"))
(set-foo-a! x 42) ; contract violation

No need to explicitly tell it a field is mutable.

3

Ah, I didn't know that - many thanks!