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Re: Rationale behind conversion of a nil prefix arg to numeric 1


From: Kaushal Modi
Subject: Re: Rationale behind conversion of a nil prefix arg to numeric 1
Date: Tue, 06 Sep 2016 14:20:02 +0000

On Tue, Sep 6, 2016, 7:22 AM Andreas Röhler <address@hidden>
wrote:

> But let's go back to the simplest case of lower p in interactive spec:
>
> What is easier to read/grasp
>
> (setq counter (or arg 1)
>
> or
>
> (setq  counter (prefix-numeric-value arg))
>
> IOW: in favor of avoiding these complex, tricky things. Let's have the
> code as explicit as possible.
>

Those 2 forms are not 100℅ equivalent. The equivalence goes only as far as
setting the default value of counter.

If the user used (interactive "p"), counter need to be set to 4 regardless
of whether the user used "C-4" as prefix or "C-u". In the former case, arg
would be "4", but in the latter case, it would be "(4)", I.e. a list, not a
number. Your simpler representation would not take care of the C-u case. If
the counter variable is used where a numeric arg is strictly required, you
will get an error. Here, prefix-numeric-value returns "4" when arg is
"(4)".

> --

Kaushal Modi


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