Possible zsh bug with unique tied vars in 4.0.4?

Possible zsh bug with unique tied vars in 4.0.4?

[Steve Simmons]

The following sequence of commands shows unexpected performance in
zsh when using tied variables and unique processing.  In brief, if
you have tied variables FOO and foo and typeset one of them to unique
(-U), you can use the other to assign non-unique values to the first.
This is counter-intuitive at best :-), and I can see no use for this
feature.  The manual page leads one strongly to believe that a single
variable is created which simply has two names and two presentations;
the experiment below shows that clearly there are other differences
as well.

In most cases this wouldn't matter as I would declare such variables
with

   $ typeset -Tx -U FOO foo

However, when applying -U to useful special vars like PATH you cannot
redeclare the overall type, nor can you simply do

   $ typeset -U PATH

as that leads to the anomalous performance as shown below.  One must
set uniqueness on both forms;

   $ typeset -U PATH
   $ typeset -U path

otherwise $PATH and $path start getting out of sync.

This lack of tieing of secondary variable characteristics may apply
to other items as well (justification, etc); I've not experimented.

I'm running zsh version 4.0.4 on FreeBDS 4.6 RC2.

Steve


superior$ typeset -Tx FOO foo
superior$ echo $FOO

superior$ echo $foo

superior$ FOO="a:b" 
superior$ echo $FOO
a:b
superior$ echo $foo
a b
superior$ foo=($foo a c)
superior$ echo $foo
a b a c
superior$ echo $FOO
a:b:a:c
superior$ typeset -U foo
superior$ echo $foo
a b c
superior$ echo $FOO
a:b:c
superior$ FOO="a:c:$FOO"
superior$ echo $FOO
a:c:a:b:c
superior$ echo $foo
a c a b c
superior$ foo=($foo)
superior$ echo $foo
a c b
superior$ echo $FOO
a:c:b
superior$ echo $ZSH_VERSION
4.0.4
superior$ uname -a
FreeBSD superior.inland-sea.com 4.6-RC FreeBSD 4.6-RC #8: Fri Jun  7 21:27:23 EDT 2002 root@superior.inland-sea.com:/usr/src/sys/compile/SUPERIOR  i386

Re: Possible zsh bug with unique tied vars in 4.0.4?

[Peter Stephenson]

Steve Simmons wrote:
> The following sequence of commands shows unexpected performance in
> zsh when using tied variables and unique processing.  In brief, if
> you have tied variables FOO and foo and typeset one of them to unique
> (-U), you can use the other to assign non-unique values to the first.
> This is counter-intuitive at best :-), and I can see no use for this
> feature.  The manual page leads one strongly to believe that a single
> variable is created which simply has two names and two presentations;
> the experiment below shows that clearly there are other differences
> as well.

I think `strongly' is an overstatement since the manual page says the
two parameters `may otherwise be manipulated as normal' and indicates
that only the scalar can be exported.  However, it's certainly not
particularly useful that -U works that way.  It's more useful with some
of the other flags where you might want different padding (-L, -R, -Z)
or you might want to hide the value (-H) for just one of the parameters,
or mark just one of them as readonly (-r), even though these are
probably less used features.  The only really good reason for not
changing this is that it makes a mess of the internals to grope around
for the alternative parameter just in the case where they are tied and
just for certain flags.  I expect the documentation could be made more
explicit, though.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 392070


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