Question

As many of you already know, PHP 5.4 alpha has been released. I have a question regarding the following.

Simplified string offset reading.
$str[1][0] is now a legal construct.

How exactly does $str[1][0] work?

EDIT: http://php.net/releases/NEWS_5_4_0_alpha1.txt

Answer 1

This is a side effect, and was mentioned in the proposal here:
http://php.markmail.org/thread/yiujwve6zdw37tpv

The feature is speed/optimization of string offsets.

Hi,

Recently I noticed that reading of
string offset is performed in two
steps. At first special string_offset
variant of temporary_variable is
created in
zend_fetch_dimension_address_read()
and then the real string value is
created in
_get_zval_ptr_var_string_offset().

I think we can create the real string
in the first place. This makes 50%
speed-up on string offset reading
operation and allows to eliminate some
checks and conditional brunches in VM.

The patch is attached (don’t forget to
regenerate zend_vm_execute.h to test
it). However it changes behavior in
one bogus case. The following code now
will emit “b” (currently it generates
a fatal error – cannot use string
offset as an array).

$str = "abs";
var_dump($str[1][0]);

I think it’s not a problem at all. “b”
makes sense because “abs”[1] -> “b”
and “b”[0] -> “b”.

I’m going to commit the patch in case
of no objections.

Thanks. Dmitry.