From: Felipe Contreras <felipe.contreras@gmail.com>
To: Bart Schaefer <schaefer@brasslantern.com>
Cc: Zsh hackers list <zsh-workers@zsh.org>
Subject: Re: The emulation rabbit-hole RE typeset/unset
Date: Sat, 28 Nov 2020 05:35:55 -0600 [thread overview]
Message-ID: <CAMP44s1b5N2_PfmQEgvXhdGzcXgLOK6i1CpABfo-XK=RGf-hRw@mail.gmail.com> (raw)
In-Reply-To: <CAH+w=7aQ_pNqHtgEqV6s02Z+V6Aih2g8hebMbjxHgdYJVKXYFQ@mail.gmail.com>
On Fri, Nov 27, 2020 at 6:37 PM Bart Schaefer <schaefer@brasslantern.com> wrote:
>
> On Fri, Nov 27, 2020 at 4:00 PM Felipe Contreras
> <felipe.contreras@gmail.com> wrote:
> >
> > This is a bit tautological, because if the variable is unset, it can't
> > be anything else but a string: param_is_unset(p) ->
> > param_type_is_string(p).
>
> This is manifestly not true in ksh and bash, because:
>
> [[ ${foo-nil} = nil ]] implies foo is unset
> { typeset -i foo } declares foo is an integer, not a string
> function ff { typeset -i foo; echo ${foo-nil}; } outputs nil
All right, that is true.
But then, if we have this:
typeset -i foo
At this point "foo" is unset (in bash and ksh). It does not have a
value, and ${foo-nil} is nil. So for all intents and purposes it is
nil.
Then, we decide to add 1 to it:
((foo += 1))
The result is 1 (in bash and ksh).
This is interesting.
Irrespective of the fact that foo is unset, you can still add 1 to it,
so in bash and ksh it doesn't matter that foo initially is *not* 0;
you can still add to it.
So this:
f() { ((foo +=1 )); echo ${foo-nil}; }
Returns the same in all shells: 1. You don't need to define "foo" first.
So the statement 'the only useful "declared but not set" variable is a
simple scalar' does not seem to be true.
An integer is not a "simple scalar", and seems to be useful unset.
Or am I missing something?
Cheers.
--
Felipe Contreras
next prev parent reply other threads:[~2020-11-28 11:36 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-25 7:02 More rabbit-holes with unset variables Bart Schaefer
2020-11-25 13:19 ` Stephane Chazelas
2020-11-25 22:17 ` Felipe Contreras
2020-11-26 6:10 ` Stephane Chazelas
2020-11-26 7:20 ` Felipe Contreras
2020-11-26 11:21 ` Oliver Kiddle
2020-11-26 11:29 ` Roman Perepelitsa
2020-11-26 19:08 ` Felipe Contreras
2020-11-26 19:29 ` Felipe Contreras
2020-11-26 21:13 ` Bart Schaefer
2020-11-26 21:31 ` Felipe Contreras
2020-11-26 23:29 ` Bart Schaefer
2020-11-26 23:32 ` Bart Schaefer
2020-11-26 23:53 ` Felipe Contreras
2020-11-27 0:23 ` Bart Schaefer
2020-11-27 1:51 ` Felipe Contreras
2020-11-27 20:01 ` Bart Schaefer
2020-11-27 21:49 ` Felipe Contreras
2020-11-27 22:06 ` Bart Schaefer
2020-11-27 23:35 ` Felipe Contreras
2020-11-26 22:07 ` Bart Schaefer
2020-11-26 20:41 ` Bart Schaefer
2020-11-26 20:49 ` Stephane Chazelas
2020-11-26 21:20 ` Felipe Contreras
2020-11-26 22:41 ` Bart Schaefer
2020-11-26 23:45 ` Felipe Contreras
2020-11-27 0:09 ` Bart Schaefer
2020-11-27 0:30 ` Felipe Contreras
2020-11-27 0:51 ` Bart Schaefer
2020-11-27 1:30 ` Felipe Contreras
2020-11-27 20:54 ` Bart Schaefer
2020-11-27 22:10 ` Felipe Contreras
2020-11-27 22:39 ` Bart Schaefer
2020-11-28 0:00 ` Felipe Contreras
2020-11-28 0:04 ` Bart Schaefer
2020-11-28 10:52 ` Felipe Contreras
2020-11-28 0:36 ` The emulation rabbit-hole RE typeset/unset Bart Schaefer
2020-11-28 11:35 ` Felipe Contreras [this message]
2020-11-28 16:56 ` Bart Schaefer
2020-12-01 8:49 ` Felipe Contreras
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