Re: [BUG] Can't mark unset variables as read-only

[Mikael Magnusson <mikachu@gmail.com>]

On Wed, Apr 29, 2015 at 12:36 PM, Peter Stephenson
<p.stephenson@samsung.com> wrote:
> On Wed, 29 Apr 2015 08:35:43 +0200
> Martijn Dekker <martijn@inlv.org> wrote:
>> Unlike other shells, zsh can't mark an unset variable as read-only.
>
> Yes, the standard does indeed require that ability.  As you can imagine,
> something like this that completely breaks the normal programming model
> of variables (a variable can't have state if it's unset because it
> doesn't exist) is a nightmare to implement; however, it can at least be
> limited to the POSIXBUILTINS option and maybe the cases using that are
> simple enough that it mostly works.  I'm sure there are any number of
> strange edge cases, though.
>
> The output of "readonly -p" is still broken (doesn't show the unset
> variables in a fashion that can be used for restoring the current state)
> but it was anyway:
>
>   typeset -ar '*'
>   *=()
>
> Er, no, I don't think that's going to work.
>
> So that can be fixed separately.

I wanted the opposite thing the other day, sort of. I have a ZLE
widget that looks at $WIDGET, and I wanted to reuse it by calling it
from another widget, setting WIDGET to another value first. However,
ZLE makes $WIDGET readonly special, and I couldn't find any
combination of flags that let me make a non-readonly local WIDGET. Is
that possible?

% zle -N h; h() { local -h WIDGET; WIDGET=hi; echo $WIDGET }; bindkey '^[h' h
% <press alt-h>
h: read-only variable: WIDGET
% zle -N h; h() { local +r -h WIDGET; WIDGET=hi; echo $WIDGET }; bindkey '^[h' h
% <press alt-h>
h:local: WIDGET: can't change type of a special parameter
% zle -N h; h() { local WIDGET; WIDGET=hi; echo $WIDGET }; bindkey '^[h' h
% <press alt-h>WIDGET=h

h: read-only variable: WIDGET

compared to
% () { readonly foo=3; () { local foo=5; echo $foo }; echo $foo }
5
3

-- 
Mikael Magnusson