Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:71670
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain gmail.com designates 209.85.216.178 as permitted sender)
MIME-Version: 1.0
Sender: happy.melon.wiki@gmail.com
In-Reply-To: <CAMyk_AbBZBzdbUB+s_sRjC_L=GVK=TJhOHqvW4nOSBDtoijRCw@mail.gmail.com>
References: <1796143171.126442.1390903281925.open-xchange@app2.ox.registrar-servers.com>
	<CALtuQzDccxhqJSgg+Ofyv6njcRhL9-UpqWrP0uB1_9uH+k=UCA@mail.gmail.com>
	<CAMyk_AbBZBzdbUB+s_sRjC_L=GVK=TJhOHqvW4nOSBDtoijRCw@mail.gmail.com>
Date: Tue, 28 Jan 2014 13:36:34 +0000
Message-ID: <CAFKLSKCA+SDwXLVxdkT2H0eYheB+WhZ98rpsL053QXXidpZ6kA@mail.gmail.com>
To: PHP internals list <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=001a11c12e4cb756d004f107e9ce
Subject: Re: [PHP-DEV] Lexical scoping
From: happy.melon.wiki+gb@gmail.com (George Bond)

--001a11c12e4cb756d004f107e9ce
Content-Type: text/plain; charset=ISO-8859-1

On 28 January 2014 13:25, Lazare Inepologlou <linepogl@gmail.com> wrote:

> 2014-01-28 Sebastian Krebs <krebs.seb@gmail.com>
>
> > 2014-01-28 Andrea Faulds <ajf@ajf.me>
> >
> > > Good morning,
> > >
> > > Perhaps a future version of PHP (PHP 6? 5.7?) could have lexical
> scoping
> > > with a
> > > "let" keyword? At the very least, it would make foreach() with a
> > reference
> > > less
> > > of a problem:
> > >
> > >     foreach ($array as let &$a) {
> > >         $a = 3;
> > >     }
> > >     // $a is not in this scope - no need to worry about accidentally
> > > changing
> > > last array item
> > >
> > > Any thoughts?
> > >
> >
> > Hi,
> >
> > My 2 cents: That is a very minor improvement at the cost of an additional
> > keyword. It is only to avoid, that you accidentally interfere with outers
> > scope variables? If it is hard to track these variables, maybe your
> > method/function is too big.
> >
> >
> I agree.
>
>
> > Regarding your example:
> >
> > foreach ($array as &$a) {
> >     $a = 3;
> > }
> > $a = null; // $a not a reference anymore. Problem solved :)
> >
> >
> Problem not solved. You have just changed the last element of $array...
> This is the exact problem that was to be avoided.
>
>
AFAIK, this is a problem which is quite limited to foreach() (are there
other examples?), so one (BC-breaking-but-probably-for-the-best) solution
would simply be to unset the variable automatically if it wasn't already
defined:

foreach( $array as &$a ){
    $a = 3;
}
var_dump( $a ); // E_NOTICE, $a is now undefined

$b = 2;
foreach( $array as &$b ){
    $b = 3;
}
var_dump( $b ); // 3, $b was defined before we started the foreach, so it's
not wiped

Alternatively, you could say that the ultimate problem is that we don't
have strong scoping - braces only define flow control, not scope.  So you
could introduce a strong-scoping structure.  Maybe a double brace?

foreach( $array as &$a ){{
    $a = 3;
}}
var_dump( $a ); // E_NOTICE, $a is now undefined

You could even say that an isolated brace pair (ie not one following a
control statement) *always* produces a scope.

--GB

--001a11c12e4cb756d004f107e9ce--