Description:
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I've done some testing of variable reference behavior in PHP and was able to 
disprove something in the documentation.  On the manual page at

http://php.net/manual/en/functions.arguments.php

there is a comment that says, "Note that passing by reference doesn't speed up 
your php script. PHP is smart enough not to simply copy data every time the 
language requires it. Rahter, PHP uses a reference and waits until the copy (a 
copied variable or a copy used in a function) is actually used as a copy and 
creates one then."

That statement is not correct in any circumstance I could come up with, except 
for a read-only function accepting a one megabyte string argument.  I observed 
massive performance improvements when using references to prevent the copy-on-
write behavior.  So, to say that passing by reference doesn't speed up your php 
script is not correct.  It is only correct to say that if a parameter is passed 
by value and never modified, then PHP wont make an extra copy of it.

Test script:
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Details posted at http://www.miqrogroove.com/writing/php-references-for-speed/