hashtable-copy(3scm)

💅 hashtable-copy — like, a whole manual page, bestie

okay so this is hashtable-copy from the Scheme Programmer's Manual (yes the 3scm one, you're in the right place 🎀), and honestly? it's giving "tiny procedure, big slay."

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✨ NAME ✨

hashtable-copy — copy a hashtable. that's it. that's the whole vibe. 🫶

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📚 LIBRARY 📚

bestie you gotta import it first, no cap:

(import (rnrs))                     ;R6RS
(import (rnrs hashtables))          ;R6RS

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🌸 SYNOPSIS 🌸

the two forms, exactly as written, don't @ me:

(hashtable-copy hashtable)
(hashtable-copy hashtable mutable)

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💖 DESCRIPTION 💖

so basically it returns a copy of hashtable. like a clone. a twin. a doppelgänger but make it functional. 👑

now here's the tea 🍓 — if the mutable argument is provided and it's true, then the returned hashtable is mutable. otherwise? it's immutable. locked. frozen. no takebacks. 💀

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🎁 RETURN VALUES 🎁

returns a single value: a hashtable. one (1) hashtable. that's the whole return. 🌈

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🌟 EXAMPLES 🌟

okay this example is actually iconic, watch:

(define (alist->eqv-hashtable alist)
  (let ((ht (make-eqv-hashtable)))
    (do ((alist alist (cdr alist)))
        ((null? alist)
         (hashtable-copy ht))
      (hashtable-set! ht (caar alist) (cdar alist)))))

like, it builds up the hashtable then copies it on the way out. main character energy honestly.

and then:

(hashtable-entries
 (alist->eqv-hashtable '((0 . zero) (1 . one) (2 . three))))
    => #(0 1 2)
       #(zero one three)

see how the entries come back? chef's kiss. 🔥 (yes, (2 . three) is in the original, it's not a typo, leave it alone 😭)

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🧠 RATIONALE 🧠

why even allow immutability? because allowing the hashtable to be immutable lets implementations create an optimized representation for the hashtable. so it's not just cute, it's efficient. iykyk. ✨

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🦋 COMPATIBILITY 🦋

this procedure is unique to R6RS. so if you're on something else? not me finding out the hard way 🙈

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💀 ERRORS 💀

this procedure can raise exceptions with the following condition types:

• &assertion (R6RS) — the wrong number of arguments was passed, or an argument was outside its domain. in particular, hashtable must be a hashtable. like, bestie, it has to actually BE a hashtable, okay?? 🫠

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👀 SEE ALSO 👀

• make-hashtable(3scm) — go read that one too, it's the whole origin story 🧚

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⭐ STANDARDS ⭐

R6RS. periodt. 💅

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🕰️ HISTORY 🕰️

this procedure first appeared in R6RS, but a similar procedure was also present in SRFI-69. so it's got lore. 📖

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👑 AUTHORS 👑

this page is part of the scheme-manpages project. it includes materials from the RnRS documents. more information can be found at https://github.com/schemedoc/manpages/. 🫶

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and that's the page!! mwah 💋 — this was hashtable-copy(3scm), dated 2023-01-22, from the Scheme Programmer's Manual (that's the source/version right there, don't say i never told you). go copy some hashtables, bestie, you got this 🦋💜