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adjust spec of impersonator? w.r.t. prop:impersonator-of

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As implemented, `impersonator?` does not recognize values that
impersponate others via `prop:impersonator-of`. Meanwhile, the use of
`impersonator?` in the (unenforced) contract of `unsafe-struct*-ref`
makes sense with that implementation, as does the offered rationale
for sometimes using `impersonator?`. So, adjust the specification in
the documentations, instead of adjusting the implementation.
This commit is contained in:
Matthew Flatt 2019-05-17 22:40:39 -04:00
parent cc487a4d9a
commit e3e141d1fd
1 changed files with 13 additions and 3 deletions
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16
pkgs/racket-doc/scribblings/reference/chaperones.scrbl
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@ -65,12 +65,20 @@ types and their instances.
@defproc[(impersonator? [v any/c]) boolean?]{
Returns @racket[#t] if @racket[v] is an @tech{impersonator}, @racket[#f] otherwise.
Returns @racket[#t] if @racket[v] is an @tech{impersonator} created by
procedures like @racket[impersonate-procedure] or
@racket[impersonate-struct], @racket[#f] otherwise.
Programs and libraries generally should avoid @racket[impersonator?] and
treat impersonators the same as non-impersonator values. In rare cases,
@racket[impersonator?] may be needed to guard against redirection by an
impersonator of an operation to an arbitrary procedure.}
impersonator of an operation to an arbitrary procedure.
A limitation of @racket[impersonator?] is that it does @emph{not}
recognize an @tech{impersonator} that is created by instantiating a
structure type with the @racket[prop:impersonator-of] property. The
limitation reflects how those impersonators cannot redirect structure
access and mutation operations to arbitrary procedures.}
@defproc[(chaperone? [v any/c]) boolean?]{
@ -78,7 +86,9 @@ impersonator of an operation to an arbitrary procedure.}
Returns @racket[#t] if @racket[v] is a @tech{chaperone}, @racket[#f] otherwise.
Programs and libraries generally should avoid @racket[chaperone?] for
the same reason that they should avoid @racket[impersonator?].}
the same reason that they should avoid @racket[impersonator?]. A true
value for @racket[chaperone?] implies a true value of
@racket[impersonator?].}
@defproc[(impersonator-of? [v1 any/c] [v2 any/c]) boolean?]{