Re: PATCH: suggestion for new condition

[Peter Stephenson <pws@xxxxxxxxxxxxxxxxx>]

Sven Wischnowsky wrote:
> 
> Dunno if you'll like this one.
> 
> I sometimes missed an easy way to check if a certain parameter was set 
> or of a specific type. The patch below adds the condition `-v' for
> this:
> 
>   `-v param'       is true if the parameter `param' is set

You can do this already with `if (( $+param )) ...'.

>   `-v param type'  is true if paramater `param' is set and of the
>                    given type; `type' may be any of: scalar, array,
> 		   integer, association, left, right, right-blank,
> 		   right-zero, upper, readonly, tag, export, and
> 		   unique

You can't do this at the moment, but maybe a more flexible way would
be to create another ${(...)} flag --- looks like t is still usable
--- and make ${(t)param} print out the type of param, so you can do
[[ ${(t)param} = (array|association)* ]], and things like that.  It's
maybe a little more transparent, and the information can be used
outside conditions.  It's a little more complicated in that you have
to have a list like "array left unique", or whatever, but if the basic
type always comes first maybe it's obvious enough.  It could return a
blank for unset.  Of course [[ ${(t)param} = *export* ]] is less
efficient than [[ -v param export ]], but I don't think that's a major
worry.  It should be reasonably easy --- the question is always quite
how to insert any new code into paramsubst(), it's a bit like deciding
where to put a needle in a haystack.

I worry a little, too, (though it maybe groundless) that overloading
conditions in the basic shell will cause unexpected results with
existing tests that ought to work, e.g. things like [[ -v = -v ]] ---
I don't mean that one doesn't actually work, I mean there are all
sorts of possibilities along those lines that can be quite complicated
to get right.  Some (many) versions ago I remember having a headache
about sh-compatibility in test, e.g. what should `test -n' mean, and
so on.

-- 
Peter Stephenson <pws@xxxxxxxxxxxxxxxxx>       Tel: +39 050 844536
WWW:  http://www.ifh.de/~pws/
Dipartimento di Fisica, Via Buonarroti 2, 56127 Pisa, Italy