Re: expanding nameref target?

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Tue, Feb 28, 2023 at 12:47 AM Oliver Kiddle <opk@xxxxxxx> wrote:
>
> Bart Schaefer wrote:
> > In ksh emulation (and history disabled), I have this working:
> >
> > % typeset -n foo=bar
> > % echo ${!foo}
> > bar
>
> Supporting ${!foo} is useful for ksh (and bash) compatibility so that
> sounds good. There are also other forms such as ${!name[@]}.

There are some significant differences between bash and ksh regarding
${!...}, I have a patch for subst.c that documents this in comments.
The simplest one is that ${!scalar} in bash works like ${(P)scalar} in
zsh, whereas in ksh it just substitutes the parameter's own name.

We already supported ksh ${!foo[@]} for associative arrays, I bolted
nameref handling into that code path (in addition to the zsh flags
path).  However, that's explicitly (and commented-ly) enabled only in
ksh emulation.  We don't support fetching the array of (normal) array
indexes anywhere, I haven't tried to add that.

> > However, that's pretty clumsy because of history expansion, so I'm
> > proposing the following for zsh native mode:
> >
> > % typeset -n foo=bar
> > % echo ${(?)foo}
>
> I would question whether it's really sufficiently useful to warrant
> that.

It does seem unlikely to be something wanted during an interactive
session.  How about if I leave it with just ${(!)foo} instead of
consuming (?) as well?

> I'm inclined to suspect that anyone who thinks they need ${!foo}
> has probably missed the point of namerefs. Unless they are writing
> something that is meta in nature to begin with

I presumed Mikael had a use-case or he wouldn't have asked about it.
It seems odd to have it available but only usable in ksh mode (e.g.,
${!...} is historically a synonym for ${(k)...}, but that doesn't make
sense for namerefs).

> > As an extension (more by accident than by design but possibly useful):
> >
> > % echo ${(?)options}
> > zsh/parameter
>
> Doesn't that lead to a conflict for a nameref defined in a module - do
> you get the module name or the target of the nameref?

You get the module until the feature is loaded, and then you get the
target of the nameref.