On Mon, Dec 21, 2020 at 7:30 PM Robby Findler <[email protected]>
wrote:
> Is Typed Racket able to prove that your use of unsafe accessors is
> actually safe?
>
On a similar note, my understanding is that, even without types, in a
program like this:
#lang racket
(struct cell (val))
(λ (x)
(if (cell? x)
(cell-val x)
...))
the compiler can optimize the use of `cell-val` guarded by `cell?` to omit
the redundant check. I think the optimized version should be as good as
`unsafe-struct-ref`.
If that's the case, the only extra invariant for `unsafe-struct*-ref` is
that it does not work on impersonators (including chaperones, IIUC). If you
need the extra performance, I think you can get it safely by declaring your
structs as `#:authentic` (or equivalently adding `prop:authentic`), which
will cause the struct types involved not to support impersonators:
`impersonate-struct` and similar functions will raise exceptions. On the
other hand, if you need to support impersonators, then it really is unsafe
to use `unsafe-struct*-ref`.
-Philip
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