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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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24
racket/collects/db/private/generic/sql-data.rkt
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@ -11,15 +11,23 @@
;; NULL
(define-values (sql-null sql-null?)
(let ()
(let ([created? #false])
(struct sql-null ()
;; must deserialize to singleton, so can't just use serializable-struct
#:property prop:serializable
(make-serialize-info (lambda _ '#())
#'deserialize-info:sql-null-v0
#f
(or (current-load-relative-directory)
(current-directory))))
#: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
#:property prop:serializable
(make-serialize-info (lambda _ '#())
#'deserialize-info:sql-null-v0
#f
(or (current-load-relative-directory)
(current-directory))))
(values (sql-null) sql-null?)))
(define (sql-null->false x)