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Date: Sat, 5 Jul 2014 15:39:16 +0800
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To: Kris Craig <kris.craig@gmail.com>
Cc: Xen <xen@dds.nl>, Levi Morrison <levim@php.net>, internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] not_null function
From: tjerk.meesters@gmail.com (Tjerk Meesters)

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On Sat, Jul 5, 2014 at 9:22 AM, Kris Craig <kris.craig@gmail.com> wrote:

> On Fri, Jul 4, 2014 at 2:38 PM, Xen <xen@dds.nl> wrote:
>
> > On Fri, 4 Jul 2014, Levi Morrison wrote:
> >
> >  For completeness, it is available in Perl and I believe Perl had it
> >> first; not completely sure though.
> >>
> >
> > Okay, I never used Perl.
> >
> >
> >  I don't think changing isset would be beneficial, sadly. I wish it
> >> only checked that a variable exists and didn't do the not null check
> >> but it's used very, very widely.
> >>
> >
> > As long as people don't have to use isset anymore to check for a
> not-null,
> > perhaps over time this widespreadedness would become less.
> >
> > As soon as you can use "unless (is_null())" to check whether a variable
> > exists and is not null, the need for using isset for this should greatly
> > diminish...
> >
> > Just my perspective. I don't know what other people think, the boogieman
> > of this list seems to not want to discuss anything related to this, so I
> > don't know.
> >
> > I mean for me it means having to rethink my thinking, i.e. to get used to
> > this new statement. But it would probably become very natural?
> >
> > I would imagine a lot of people becoming enthusiastic about an "unless"
> > statement. It is also a sexy thing to introduce and it doesn't require
> any
> > changes to existing code.
> >
> > Again, just my perspective. Curious what other people really think at
> this
> > point.
> >
> > Regards, Bart
> >
> >
> > --
> > PHP Internals - PHP Runtime Development Mailing List
> > To unsubscribe, visit: http://www.php.net/unsub.php
> >
> >
> I'm not much into Perl or Ruby, either, but I agree that an unless keyword
> would be a very nice thing to have.  However, I'm still not sure how that
> would solve the isset problem.  If the variable doesn't exist, are you
> saying that encapsulating it within the unless arg would prevent an
> undefined variable notice from being thrown?  If so, could someone
> elaborate on why that is?  And if not, then while I do agree it's a good
> idea on its own merits, I don't think it solves the issue we're mulling
> over here.
>
> Currently, this is what's available for checking a variable's status
> without throwing any errors:
>
> Variable exists and !== NULL:  isset( $var )
> Variable === NULL or doesn't exist:  !isset( $var )
> Variable == NULL or doesn't exist:  empty( $var )
> Variable exists and != NULL:  !empty( $var )
> Variable exists (including NULL):  ????
>

Yep, nothing exists for that; we have a whole bunch of `_exists()`
functions, but not e.g. `variable_exists()` or even a dedicated `exists`
opcode.


> Variable exists and === NULL:  ????
>

That's simply `@$var === null` or `@is_null($var)` of course ;-)


>
> It's those last two cases that we currently don't have any streamlined
> approach for.  If a variable is NULL and you use isset() on it, the return
> will be FALSE.  So if you were to do something like isset( $var ) && $var
> === NULL, that statement will always return FALSE, even you set the
> variable with $var = NULL beforehand.  You'll get the same problem using
> empty().  In other words, as far as I can tell, there's currently no way to
> tell if a variable is set and NULL (or just set with any value including
> NULL) in PHP.
>
> The closest thing I could find that accomplishes this is property_exists().
>  That function will return TRUE even on NULL values.  But as I understand
> it, that function only works on properties; i.e. variables that are a part
> of a class.  There doesn't seem to be any option for doing this with
> procedural variables.  We know that setting a variable to NULL in PHP is
> not the same as unsetting it because referring to it later won't throw an
> undefined notice, but aside from catching that notice itself, there doesn't
> seem to be any way to accomplish this.  Am I missing something?  I realize
> it's an edge case, but it still needs to be covered.
>
> --Kris
>



-- 
--
Tjerk

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