bytevector-copy!(3scm)

💅 bytevector-copy!(3scm) — the Scheme Programmer's Manual, but make it cute 🎀

okay bestie, so this page lives in the Scheme Programmer's Manual and it's all about bytevector-copy! — the little icon that copies bytes between bytevectors ✨

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🌸 NAME 🌸

bytevector-copy! — copy bytes between bytevectors, no cap 💖

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📚 LIBRARY 📚

import it from whichever flavour of Scheme you're on, queen:

(import (rnrs))                     ;R6RS
(import (rnrs bytevectors))         ;R6RS
(import (scheme base))              ;R7RS

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✨ SYNOPSIS ✨

two whole vibes, one name. pick your fighter:

(bytevector-copy! source source-start target target-start k)  ;R6RS
(bytevector-copy! to at from start end)                       ;R7RS

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🦋 DESCRIPTION 🦋

R6RS — copies the bytes from source at indices source-start, …, source-start + k − 1 to consecutive indices in target starting at target-index. literally just sliding bytes over, periodt 💫

R7RS — copies the bytes of bytevector from between start and end to bytevector to, starting at at. same energy, different arg list, iykyk 🌈

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🫶 RETURN VALUES 🫶

Returns unspecified values. like, don't expect a gift back, it's giving "the journey is the reward" 😌

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🍓 EXAMPLES 🍓

R6RS — watch it work:

;; R6RS
(let ((b (u8-list->bytevector '(1 2 3 4 5 6 7 8))))
  (bytevector-copy! b 0 b 3 4)
  (bytevector->u8-list b))
   => (1 2 3 1 2 3 4 8)

R7RS — same slay, different signature:

;; R7RS
(define a (bytevector 1 2 3 4 5))
(define b (bytevector 10 20 30 40 50))
(bytevector-copy! b 1 a 0 2)
   => #u8(10 1 2 40 50)

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👑 APPLICATION USAGE 👑

this procedure is common in (de)serialization and processing of binary data 🔥 ngl tho, sometimes keeping track of all those indices gets mad cumbersome, and bytevector ports are lowkey more suitable in those situations 💀

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💀 COMPATIBILITY 💀

okay this is the important tea ☕ — R6RS and R7RS specify very different arguments for these procedures. and note in particular that it's not just a different argument order, the last argument is also different. so don't be out here mixing them up, bestie, that's a whole different function in your head 🙈

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🧚 ERRORS 🧚

this procedure can raise exceptions with the following condition types:

• &assertion (R6RS) — the wrong number of arguments was passed, an argument was outside its domain, or the byte ranges were not valid with regard to the bytevector lengths. red flag behaviour, honestly 🚩

R7RS — the assertions described above are errors. Implementations may signal an error, extend the procedure's domain of definition to include such arguments, or fail catastrophically. yes, catastrophically, dramatic much 😭

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⭐ SEE ALSO ⭐

• bytevector-copy(3scm) — the non-destructive sibling, go say hi 🫶

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🌈 STANDARDS 🌈

R6RS, R7RS. both certified iconic 👑

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💜 HISTORY 💜

the arguments used by R7RS are consistent with SRFI-43 whereas R6RS is consistent with SRFI-66. ancient lore, fr fr 📜

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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/. shoutout to the maintainers, main character energy fr 💅

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🔥 BUGS 🔥

implementations need to be careful to handle the case where the source and target bytevector ranges overlap in memory. that's the one place this gets spicy 🌶️ overlap = chaos if you're not paying attention, so bestie please be careful 😭

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ok that's the whole page!! no notes, 10/10, ate and left no crumbs 🍓✨

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sign-off time 💖 this lil rewrite is from the 2021-02-20 edition of the Scheme Programmer's Manual — bytevector-copy!(3scm), mwah, see you in the group chat 💅🦋