From: ludo@gnu.org (Ludovic Courtès)
To: guile-user@gnu.org
Subject: Re: What should the constructor for a record look like?
Date: Mon, 27 Aug 2018 14:22:38 +0200 [thread overview]
Message-ID: <87pny49ey9.fsf@gnu.org> (raw)
In-Reply-To: 1617672.9nuLs2ACSm@aleksandar-ixtreme-m5740
Hi,
HiPhish <hiphish@posteo.de> skribis:
> Hello, it's me again, the guy who wants to implement MessagePack [1] in Guile.
> The specification defines a type of "extension" [2], a pair of an 8-bit
> integer and a byte array for data. Implementing this type as a record is
> obvious, but what should be the name of the constructor?
>
> (define-record-type ext
> (make-ext type data)
> ext?
> (type ext-type)
> (data ext-data))
>
> Either `make-ext` or just `ext` seem appropriate.
For immutable records (which should be the norm :-)), I often leave out
‘make-’ nowadays. (The analogy is ‘string’ vs. ‘make-string’, for
instance.)
> I have seen both types of constructors, what do you guys say? And
guys and gals :-)
> while I'm on the topic, what about types? An extension is only valid
> if the first field (type) is an integer from -128 to 127 and the data
> a vector of bytes (integer in the range from 0 to 255). How do I
> enforce this invariant without static typing?
You could enforce it by not exporting the raw record constructor, and
instead exporting a procedure that performs all the necessary checks:
(define-record-type <ext>
(%ext type data) ;private
ext?
…)
(define (ext type data) ;public
(assert-valid-arguments type data)
(%ext type data))
HTH!
Ludo’.
prev parent reply other threads:[~2018-08-27 12:22 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-26 13:04 What should the constructor for a record look like? HiPhish
2018-08-26 16:11 ` Matt Wette
2018-08-27 12:22 ` Ludovic Courtès [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.gnu.org/software/guile/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87pny49ey9.fsf@gnu.org \
--to=ludo@gnu.org \
--cc=guile-user@gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).