Re: Associative arrays and memory

[Peter Stephenson <pws@xxxxxxxxxxxxxxxxx>]

"Bart Schaefer" wrote:
> } It does seem the existing ztrdup()'s in what's now copyparam() are
> } memory leaks.  This will need fixing in any case, independently from
> } assoc arrays.
> 
> I'm not so sure any more.  When restore_params() is called, it uses the
> pm->sets functions to assign directly to the struct param already in the
> paramtab.  So that memory is now owned by the paramtab and should be
> freed when the param next becomes unset ... right?

Yes, it looks like you're right.  Maybe it's still unnecessarily
confusing.  The struct param is really just a placeholder with a type
flag for the real information.

> zagzig<17> HISTSIZE=1000 
> zagzig<18> HISTSIZE=0 echo hello
> hello
> zagzig<19> echo $HISTSIZE
> 2

This seems to be OK after restoring the old behaviour, so I haven't
look further into what had gone wrong.

> } There are currently no special assoc arrays, of course, and it should
> } probably be possible to prevent there being any
> 
> What about the discussion that started all this -- using an associative
> array to give user access to shell-internal completion data?

Rats, I just looked at zle_params.c and you're right --- they're
marked special.  I had wrongly assumed it was just a case of setting
the value at the start and using it at the end, but there tied to
functions.

That doesn't mean assoc arrays need to be the same, though.  The case
that needs worrying about is the following:

  hash=(?...?) builtin_or_func

where the ?...? represents whatever we pick for whole array
assignments.  If there is none, there's no problem; that's the only
case where copying parameters is necessary.

There's also no problem if the hash is simply used for storing
information and is not tied to special variables or functions.  You
only need a special mechanism for restoration for something like
$path, where there's an internal variable that needs setting; simply
restoring the struct param won't do that.  If we can agree that use of
assoc arrays is simply going to be by direct access to the parameter
we can avoid ever copying it: the above shell pseudocode simply makes
the supplied $hash available for the duration of builtin_func.  It
would certainly keep things much simpler, and I can provide a patch
straight away.

So, the question is are there any uses for special hashes which would
require tying them directly to an internal variable or function, or
can they always be accessed by the standard parameter functions?  I
would think the whole point of using assoc arrays is to avoid any
unpleasantness of the former kind.  Probably Sven can answer that
better than anyone.

-- 
Peter Stephenson <pws@xxxxxxxxxxxxxxxxx>       Tel: +39 050 844536
WWW:  http://www.ifh.de/~pws/
Dipartimento di Fisica, Via Buonarroti 2, 56100 Pisa, Italy