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27 Structs

Ryan Culpepper <ryanc@racket-lang.org>

This library is unstable; compatibility will not be maintained. See Unstable: May Change Without Warning for more information.

 (require unstable/struct) package: base


(make struct-id expr ...)

Creates an instance of struct-id, which must be bound as a struct name. The number of exprs is statically checked against the number of fields associated with struct-id. If they are different, or if the number of fields is not known, an error is raised at compile time.


> (define-struct triple (a b c))
> (make triple 3 4 5)


> (make triple 2 4)

eval:4:0: make: wrong number of arguments for struct triple

(expected 3, got 2)

  in: (make triple 2 4)


(struct->list v [#:on-opaque on-opaque])  (or/c list? #f)

  v : any/c
  on-opaque : (or/c 'error 'return-false 'skip) = 'error
Returns a list containing the struct instance v’s fields. Unlike struct->vector, the struct name itself is not included.

If any fields of v are inaccessible via the current inspector the behavior of struct->list is determined by on-opaque. If on-opaque is 'error (the default), an error is raised. If it is 'return-false, struct->list returns #f. If it is 'skip, the inaccessible fields are omitted from the list.


> (define-struct open (u v) #:transparent)
> (struct->list (make-open 'a 'b))

'(a b)

> (struct->list #s(pre 1 2 3))

'(1 2 3)

> (define-struct (secret open) (x y))
> (struct->list (make-secret 0 1 17 22))

struct->list: expected argument of type <non-opaque struct>;

given: (secret 0 1 ...)

> (struct->list (make-secret 0 1 17 22) #:on-opaque 'return-false)


> (struct->list (make-secret 0 1 17 22) #:on-opaque 'skip)

'(0 1)

> (struct->list 'not-a-struct #:on-opaque 'return-false)


> (struct->list 'not-a-struct #:on-opaque 'skip)