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php

references in arrays

php.internals

Ron Korving

20 years ago

Hi,

For performance' sake, I have to know if this is true:

Is it the case that when I do this:

<?php
$array = array("one" => array(0,1,2), "two" => array(4,5,6));
$one = $array["one"];
?>

That $one is not a copy, but a reference to $array["one"] and will only
become a copy when I alter the contents of $one? I know this is the case for
regular variables, but does this also go for contents of arrays? If not, I
need to use the ampersand like I used to. But if it really is just a
reference, that would be good to know as I shouldn't be using the ampersand
at all (mistakingly thinking it's a performance advantage when it's actually
not).

Thanks,

Ron

Zeev Suraski

20 years ago

At 13:35 15/09/2005, Ron Korving wrote:

>Hi,
>
>For performance' sake, I have to know if this is true:
>
>Is it the case that when I do this:
>
><?php
>   $array = array("one" => array(0,1,2), "two" => array(4,5,6));
>   $one = $array["one"];
>?>
>
>That $one is not a copy, but a reference to $array["one"] and will only
>become a copy when I alter the contents of $one?

That's correct.

>I know this is the case for
>regular variables, but does this also go for contents of arrays? If not, I
>need to use the ampersand like I used to. But if it really is just a
>reference, that would be good to know as I shouldn't be using the ampersand
>at all (mistakingly thinking it's a performance advantage when it's actually
>not).

Generally, using & where it's not necessary is more often than not a
performance disadvantage, and not an advantage.  You should never use & for
better performance, only if you need it for applicative usage.  The engine
would do its best to do the least copying on its own.

Zeev

Ron Korving

20 years ago

Perfect :)
I've been doing it wrong all the time, thinking I was improving performance.
It's good to know how things really work under the hood.

Thanks,

Ron


"Zeev Suraski" <zeev@zend.com> schreef in bericht
news:5.1.0.14.2.20050915141221.0605b540@localhost...

> At 13:35 15/09/2005, Ron Korving wrote:
> >Hi,
> >
> >For performance' sake, I have to know if this is true:
> >
> >Is it the case that when I do this:
> >
> ><?php
> >   $array = array("one" => array(0,1,2), "two" => array(4,5,6));
> >   $one = $array["one"];
> >?>
> >
> >That $one is not a copy, but a reference to $array["one"] and will only
> >become a copy when I alter the contents of $one?
>
> That's correct.
>
> >I know this is the case for
> >regular variables, but does this also go for contents of arrays? If not,

I

> >need to use the ampersand like I used to. But if it really is just a
> >reference, that would be good to know as I shouldn't be using the

ampersand

> >at all (mistakingly thinking it's a performance advantage when it's

actually

> >not).
>
> Generally, using & where it's not necessary is more often than not a
> performance disadvantage, and not an advantage.  You should never use &

for