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From: Stefan Monnier via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>
To: help-gnu-emacs@gnu.org
Subject: Re: Defaulting optional numeric and string arguments
Date: Thu, 12 Sep 2024 15:17:33 -0400	[thread overview]
Message-ID: <jwvh6akhegh.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: t6ia3DSNEL_LDm6VVf6Y61S9lGTj6nrMeqF0b9SdM3EWiK82UxFaqE408gmEoFMuNQrbna-oEPkFI0M0whTjMzsJTu82Ih10XK0dkyeD7mA=@protonmail.com

> I have an optional numeric argument n passed to a function. 
>
> Am having difficulty setting a default for it to cater for both the 
> interactive and non-interactive cases.
>
> Is the below how to do it ?   
>
>   (setq n (if (or (not n) (not numberp n)) 0 n))

Traditionally the default numeric value for an absent prefix arg is
1 rather than 0.  So if you can arrange to use 1 as default, it'll
integrate better into the overall Emacs experience.

Also you can simply the above to

    (unless (numberp n) (setq n 0))

> I also have an optional string bfrn, to which I am using
>   (setq bfrn  (if (or (not bfrn) (string= bfrn "")) "Context" bfrn))

I'd recommend to ignore the "" case (i.e. change your callers and/or the
interactive spec so they don't accidentally send the empty string
(e.g. use `read-string` rather than `read-from-minibuffer`)) and
just use:

    (unless bfrn (setq bfrn "Context"))


- Stefan




  reply	other threads:[~2024-09-12 19:17 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-09-12 17:39 Defaulting optional numeric and string arguments Heime
2024-09-12 19:17 ` Stefan Monnier via Users list for the GNU Emacs text editor [this message]
2024-09-12 20:00   ` Heime
2024-09-12 20:18     ` Stefan Monnier
2024-09-12 20:29       ` Heime

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