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Date: Mon, 24 Jul 2006 10:53:27 -0700
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Subject: Re: [PHP-DEV] Pass by reference (5.1.1 vs 5.1.2)
From: truth@proposaltech.com (Todd Ruth)

It looks like
http://www.php.net/manual/en/language.operators.assignment.php
could use a bit of updating.  A paragraph about php 5 or a
link to the semantics changes for php 5 would help newbies.
The text about php4 says there is copy on assignment, which
implies a performance hit for using = instead of =&, but I
believe "copy on change" is more accurate.  It wouldn't hurt
to explicitly say that "=" is generally better than "=&"
(unless you really need an alias).  A user comment has been
there unchallenged for over 2 years saying you can pass an
assignment as a reference to a function, so it isn't surprising
that someone considered the 5.1.1 to 5.1.2 change an issue.
(Not that a user comment should bind the php devs, but when
the comment goes unchallenged, it can lead to false impressions.)
Perhaps some text explaining the assignment returns an r-value
would be helpful.  (If people understand "($x = 1) = 2;"
shouldn't work, they might understand that passing "$x=1" to
a function by reference shouldn't affect $x.  (or should
"($x = 1) = 2;" work and 5.1.2 had a real bug?))

I have to say the documentation for php is completely awesome
and is a major factor in our company using the language.  I
just point out the above to help; it isn't a complaint.

BTW, I disagree with the post below that indicates the issue is
the order of calling.  There is no way to call a function
before doing the work in the argument list.  If I call f(1+2),
I can be sure the computation to get 3 will be performed
_before_ calling f.  The issue with f($p=array()) is that
"$p=array()" is an r-value.

- Todd

On Mon, 2006-07-24 at 19:16 +0200, Johannes Schlueter wrote:
> Hi,
> 
> On Monday 24 July 2006 17:52, Rishad Omar wrote:
> >     getArray($p = array());
> 
> Here you are relying on undefined behavior. It is not defined wether $p = 
> array() or the function call getarray($p) should be executed first so the 
> order might always change.
> 
> You should always use the two lines
>      $p = array();
>      getArray($p);
> to be safe.
> 
> johannes
> 
-- 
Todd Ruth <truth@proposaltech.com>