Re: Another push on declarednull branch

[Felipe Contreras <felipe.contreras@xxxxxxxxx>]

On Mon, Dec 28, 2020 at 4:53 PM Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx> wrote:
>
> On Mon, Dec 28, 2020 at 1:46 PM Felipe Contreras
> <felipe.contreras@xxxxxxxxx> wrote:
> >
> > On Mon, Dec 28, 2020 at 2:54 PM Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx> wrote:
> > >
> > > Would it make more sense as PM_IMPLICIT, so PM_NULL = (PM_IMPLICIT|PM_UNSET)?
> >
> > It's still the same problem isn't it? Why does typeset turn on
> > PM_IMPLICIT, and unset off?
>
> Typeset turns on PM_IMPLICIT because there's nowhere else that needs to.

Yes, but why PM_IMPLICIT?

The word "implicit" means unexpressed, or implied. There's nothing
implied about "typeset"; it's expressly declaring a variable.

> Unset turns it off because the variable explicitly ceases to exist;
> only its scope remains, if it had one.

Yes, the variable "ceases to exist", but it's not any less implicit.

> > Moreover, implicit what?
>
> Implicit(ly) whatever-other-flags-are-there.

I presume that doesn't apply to PM_INTEGER, PM_LOCAL, or pretty much
any flag that is not PM_UNSET.

In other words: PM_UNSET is the only flag that can be explicit, or implicit.

> > The true meaning is PM_UNSET_BUT_VALID, because the only time this
> > flag does something is when PM_UNSET is on.
>
> I don't think "valid" is a significantly more accurate description.
> $thing is "valid" whether or not you've declared "typeset thing".

Yes, but that's my point; currently (as in; in master) "valid"
variables are implicitly the ones that are !PM_UNSET, now that concept
is changing.

> Anyway, I conceived PM_DECLARED (now for this discussion PM_IMPLICIT)
> as having a meaning independent of PM_UNSET; for example
> PM_IMPLICIT|PM_INTEGER means that if you assign to the variable, the
> value is interpreted as a number.
>
> That was before I realized that "unset foo" forgets everything about
> "foo" except its scope.  That is, I began from the position that
>
>   typeset -f foo
>   unset foo
>   foo=0.3
>
> needed to resurrect foo as a float rather than a string ... but it
> doesn't, in bash/ksh.  Hence unset must erase PM_IMPLICIT along with
> everything else.

OK. So now it only makes sense with PM_UNSET.

> > I think that's a clear sign the logic is not correct.
> >
> > It's the other way around
>
> Unfortunately given the bitwise implementation that condition is much
> more complicated to test for; the reversal is for convenience.  Zsh is
> full of bitfield-like booleans that mean nothing unless combined with
> other such booleans.

Sure, but PM_NULL can fulfill that purpose perfectly fine (instead of
PM_DECLARED).

-- 
Felipe Contreras