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Date: Thu, 15 Mar 2012 17:54:14 +0100
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To: Patrick ALLAERT <patrickallaert@php.net>
Cc: Klaus Silveira <klaussilveira@php.net>, PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Small question about performance
From: nikita.ppv@googlemail.com (Nikita Popov)

On Thu, Mar 15, 2012 at 5:22 PM, Patrick ALLAERT <patrickallaert@php.net> w=
rote:
> 2012/3/15 Nikita Popov <nikita.ppv@googlemail.com>:
>> If I am understanding the text correctly it is saying that
>> =A0 =A0$f1 =3D f1();
>> =A0 =A0$f2 =3D f2($f1);
>> =A0 =A0$f3 =3D f3($f2);
>> is using more memory than
>> =A0 =A0$f3 =3D f3(f2(f1()));
>>
>> For me this doesn't make any sense. In the latter case PHP will also
>> create temporary variables to store the return values. There should be
>> no difference in memory consumption.
>
> It does make sense to me.
>
> In the first case, when calling f3(), $f1 is still referenced.
> In the second case, when calling f3(), the result of f2() is
> referenced, but there is no more active reference to the result of
> f1().
I don't really know when PHP frees temporary variables, but my guess
was that they are freed when the scope is left.

If that is not true, then forget whatever I said.

But if it is true, then there is no inherent difference between the
two version. The only difference is that explicit $variables would
need an entry in the active symbol table, which is pretty much
negligible.