From: Jun T <takimoto-j@kba.biglobe.ne.jp>
To: zsh-workers@zsh.org
Subject: a few question about named reference
Date: Thu, 13 Jul 2023 13:05:50 +0900 [thread overview]
Message-ID: <083477A3-A5D3-49B1-BF6F-D148C6BCAA54@kba.biglobe.ne.jp> (raw)
[1] what does 'typeset -n ref' do when a variable 'ref' already exists?
(1a) removing a named reference
In the section NAMED REFERENCE in zshparam(1),
... so to remove a
named reference, use either `unset -n pname' or one of:
typeset -n pname
typeset +n pname
followed by
unset pname
But:
% i=10
% typeset -n pname=i
% typeset -p pname
typeset -n pname=i
# now try to remove pname
% typeset -n pname # this does nothing
% typeset -p pname
typeset -n pname=i # still points to i
% unset pname
% typeset -p i pname
typeset: no such variable: i
typeset -n pname=i
The following works:
% typeset -n pname= # reset to empty
% unset pname
% typeset -p pname
typeset: no such variable: pname
Just fix the document?
(1b) converting a scalar into named reference
In the first post by Bart about the named reference (worker/51360):
> One difference from ksh93 is that you can't convert scalars into
> namerefs
But it seems we can convert a scalar into nameref:
% i=10
% ref=i
% typeset -n ref
% echo $ref
10
I have no idea whether the conversion needs be prohibited or not.
[2] readonly named reference
% typeset -nr ref=i
% typeset -n +r ref
typeset: no other attributes allowed with -n
% typeset +n ref
typeset: ref: read-only reference
% unset -n ref
zsh: read-only variable: ref
So we can't remove the readonly attribute (and will not be able
to remove/unset it). Is this intentional?
[3] can named reference be in 'unset' state?
If typeset_to_unset is on, creating namerefs with and without =''
have some difference:
% setopt typesettounset
% typeset -n r1 r2=
% typeset -p r1 r2
typeset -n r1
typeset -n r2=''
% echo ${(\!)r1-unset}
unset
So it seems r1 is 'unset'. But:
% echo ${+r1} # or just "echo $r1"
1
% typeset -p r1
typeset -n r1='' # now it is set to ''
It seems resolve_nameref() in params.c resets the PM_UNSET bit.
I feel it would be simpler to ignore typesettounset when creating
a nameref.
next reply other threads:[~2023-07-13 4:06 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-13 4:05 Jun T [this message]
2023-07-13 6:12 ` Bart Schaefer
2023-07-16 5:09 ` Jun T
2023-07-16 17:15 ` Bart Schaefer
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