Here's an implementation to try:
https://github.com/racket/racket/pull/1689
So far, I like "authentic" better than the alternatives, so the PR uses
that term.
If you try something like
(struct posn (x y))
(time
(let ([p (posn 1 -1)])
(for/fold ([n 0]) ([i (in-range 100000000)])
(+ (+ n (posn-x p)) (posn-y p)))))
then the difference with `#:authentic` is in the noise. But with an
example that involves more code, as below, then you can see a 5-10%
overall effect (even though the number of relevant field accesses is
the same).
----------------------------------------
#lang racket/base
(require (for-syntax racket/base))
(struct posn (x y)
#:authentic)
(define-syntax (dispatch stx)
(syntax-case stx ()
[(_ e body)
(let ([bits 5]) ; <- determines amount of code
(with-syntax ([(c ...) (for/list ([i (expt 2 bits)])
i)]
[mask (sub1 (expt 2 bits))])
#'(case (bitwise-and e mask)
[(c) body] ...)))]))
(time
(let ([p (posn 1 -1)])
(for/fold ([n 0]) ([i (in-range 100000000)])
(dispatch
i
(+ (+ n (posn-x p)) (posn-y p))))))
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