Here's an example:
#lang racket
(define (make-final-struct-type name count)
(define-values (type constructor predicate accessor mutator)
(make-struct-type name #f count 0))
(values (chaperone-struct-type type (λ _ (error 'fail1))
(λ _ (error 'fail2))
(λ _ (error 'fail3)))
constructor predicate accessor mutator))
(define-values (struct:x make-x x? x-ref x-set!)
(make-final-struct-type 'x 2))
(define-values (struct:y make-y y? y-ref y-set!)
(make-struct-type 'y struct:x 0 0))
(make-x 0 0)
(make-y 0 0)
Sam
On Fri, Nov 4, 2016 at 4:54 PM, Sam Tobin-Hochstadt
<[email protected]> wrote:
> Look at `chaperone-struct-type`:
> http://docs.racket-lang.org/reference/chaperones.html?q=chaperone-struct-type#%28def._%28%28quote._~23~25kernel%29._chaperone-struct-type%29%29
>
> You can just have the guard always error.
>
> Sam
>
> On Fri, Nov 4, 2016 at 4:49 PM, Alex Knauth <[email protected]> wrote:
>>
>>> On Nov 4, 2016, at 4:43 PM, Sam Tobin-Hochstadt <[email protected]>
>>> wrote:
>>>
>>> Typed Racket chaperones the struct type to prevent further extension.
>>
>> Ok, thanks. Where would I go to see how I would create a chaperone like this?
>>
>>> Sam
>>>
>>> On Fri, Nov 4, 2016 at 4:29 PM, Alex Knauth <[email protected]> wrote:
>>>> Hello,
>>>>
>>>> Is there a way to enforce that a particular struct is final, in other
>>>> words, that no one can declare a sub-struct of it?
>>>>
>>>> (struct foo (a b c) #:final)
>>>>
>>>> (struct bar foo (d e f))
>>>> ; should produce a syntax error similar to:
>>>> ; struct: cannot inherit from the final struct foo
>>>>
>>>> (make-struct-type 'bar struct:foo 3 0)
>>>> ; should produce an error at runtime:
>>>> ; make-struct-type: cannot inherit from the final struct foo
>>>>
>>>> Does struct have a feature like this? If I'm remembering correctly, Typed
>>>> Racket does something to make sure that untyped structs can't inherit from
>>>> typed structs. What does Typed Racket do to do do that?
>>>>
>>>> Alex Knauth
>>>>
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