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Make sql-null a transparent struct.

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This allows it to cooperate better with Typed Racket, particularly
regarding the `Any` type. The guard and use of `#:authentic` also
check that it's still a singleton in all cases.
This commit is contained in:
Sam Tobin-Hochstadt 2019-03-05 14:36:14 -05:00 committed by Ryan Culpepper
parent de82588e08
commit 25efc68b17
1 changed files with 16 additions and 8 deletions
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10
racket/collects/db/private/generic/sql-data.rkt
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@ -11,8 +11,16 @@
;; NULL ;; NULL
(define-values (sql-null sql-null?) (define-values (sql-null sql-null?)
(let () (let ([created? #false])
(struct sql-null () (struct sql-null ()
#:transparent
#:authentic
#:guard (lambda (n)
(when created?
(error 'sql-null "cannot create new instances of sql-null"))
(set! created? #true)
(values))
#:property prop:custom-write (lambda (v p w?) (write-string "#<sql-null>" p))
;; must deserialize to singleton, so can't just use serializable-struct ;; must deserialize to singleton, so can't just use serializable-struct
#:property prop:serializable #:property prop:serializable
(make-serialize-info (lambda _ '#()) (make-serialize-info (lambda _ '#())