From: Bart Schaefer <schaefer@brasslantern.com>
To: Zsh hackers list <zsh-workers@zsh.org>
Subject: Re: namerefs to var[idx]
Date: Fri, 8 Mar 2024 10:30:02 -0800 [thread overview]
Message-ID: <CAH+w=7bD5CXBzXW28_RO3g_041zJ3UeNjpqGFJKbXkdvOjnf5g@mail.gmail.com> (raw)
In-Reply-To: <20240308132307.xvc3mh4uo67wvr4x@chazelas.org>
On Fri, Mar 8, 2024 at 5:23 AM Stephane Chazelas <stephane@chazelas.org> wrote:
>
> $ f() { typeset -nu v=$1; echo $v[1]; }
> $ f 'a[2,3]'
> f: no matches found: bc[1]
Things are pretty tangled here: paramsubst() calls fetchvalue(). In
${v[1]} the entire reference is handled by fetchvalue(). In $v[1],
the $v is handled by fetchvalue() and then the [1] is handled by
paramsubst(). So it ends up being treated as $a[2,3][1], which
produces the same error. I can't immediately think of any way to fix
that without breaking something else ... ideally we'd make $a[2,3][1]
work instead, but that's a pretty large change.
In the assignment case ...
> $ f() { typeset -nu v=$1; v[1]=foo; }
... the left side of the assignment is interpreted more like ${v[1]}
than like $v[1], so everything "works." I guess one must remember
that omitting the braces around subscript expansions has always been a
shortcut rather than "the right way to do it". The braces are
required for correct handling of namespaces, too.
> $ a=12345
> $ f 'a[2,3]'
> $ echo $a
> 1foo45
>
> In that one could expect the first character of the "23"
> substring to be changed
I say "more like" above because:
% a[2,3][1]=b
zsh: no matches found: a[2,3][1]=b
% typeset 'a[2,3][1]'=c
zsh: not an identifier: a[2,3][1]
So using a nameref that way is rather a back door around the check for
identifiers.
This is an interesting variation:
% f() { typeset -n x='v[2]'; typeset -nu v=$1; x=foo; typeset -p v x }
% f 'a[2,3]'
typeset -un v='afoo2,3]'
typeset -n x='v[2]'
So chaining subscripted namerefs isn't really working, probably
because of something similar to the paramsubst()/fetchvalue() division
of labor just mentioned.
prev parent reply other threads:[~2024-03-08 18:30 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-08 13:23 Stephane Chazelas
2024-03-08 18:30 ` Bart Schaefer [this message]
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