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To: Michael Morris <tendoaki@gmail.com>, "internals@lists.php.net"
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Date: Sat, 03 Jun 2017 18:21:05 +0200
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Subject: Re: [PHP-DEV] RFC proposal
From: johannes@schlueters.de (Johannes =?ISO-8859-1?Q?Schl=FCter?=)

On Fr, 2017-06-02 at 13:12 -0400, Michael Morris wrote:
> What about foreach by reference, which is honestly the only time I
> use referencing anymore...
> 
> foreach ($array as $key => &$value) {
>   $value = someOp($value);
> }
> 
> Is this also bad?

If someOp() takes parameters by value this code disables copy-on-write
and during the function call $value has to be duplicated. If the
iteration would use values then copy-on-write can be effective and
avoid copying.

But for modification this indeed is a case where references might be
useful, in the simplified example.

foreach ($array as $key => &$value) {
   $value++;
}

is nicer and faster than (at least in my expectation, haven't measured)

foreach ($array as $key => &$value) {
   $arry[$key] = $value+1;
}

Some might argue that using array_map() would be even nicer style, while then we have more function calls (even though internally cached lookups so they are a bit faster than direct function calls)

For a larger and more realistic case the performance calculation becomes complicated, but often the extra copies cost more. But then again since PHP 7 for "simple types" a copy is relatively cheaper than before. (actually they don't have copy-on-write anymore, but references still need special treatment ...)

johannes