On Thu, Jan 28, 2010 at 11:41:43AM -0000, Ford, Mike wrote:

> > -----Original Message-----
> > From: Rene Veerman [mailto:rene7...@gmail.com]
> > Sent: 27 January 2010 22:46
> > 
> > And if your script needs to pass large (> 5Mb) arrays around to
> > functions, be sure to use passing-by-reference; failing to do so can
> > double your memory requirements,
> > possibly hitting the ini_set('memory_lmit', ??)
> Have you benchmarked this? PHP's copy-on-change philosophy means there 
> shouldn't be much difference in memory terms -- so unless you actually expect 
> to change the array's contents, you should pass by value.
> As proof, I constructed this little test:

> All in all, there is no evidence that passing arrays to functions by value is 
> inherently more expensive than by reference, and in fact in some cases it can 
> be significantly cheaper. Which in turn says that you should only pass 
> arguments by reference when you actually expect to change them, which is 
> after all what the by-reference operator is there for in the first place! QED.

Counter-intuitive benchmarks. Can we not? Benchmarking something on a
given version of PHP is nice, but changes to the PHP engine occur on a
relatively routine basis. Shall we benchmark each "tip" each time we
change PHP versions, and then rework all our code to conform to the
latest benchmark, depending on the version of PHP our code is running

A better example might be the use of single, versus double quotes.
Regardless of benchmarks, it's logically obvious that if the PHP engine
doesn't have to evaluate the contents inside single quotes, an
expression's evaluation should take less time and use fewer system
resources. Naturally, the PHP engine could be tweaked to equalize
evaluation between single- and double-quote expressions. But this could
also change as the PHP engine is changed.

To put it more simply, we can say that, depending on the version of PHP,
single-quoted versus double-quoted expressions will be evaluated in
equal amounts of time and using equivalent system resources. And if you
prefer to double-quote everything, by all means do so. But the fact
remains that the documentation for PHP says that the contents of a
string delimited by single quotes will not be evaluated, whereas those
within double quotes will be.

What these tips are about is coding things using best practices, derived
from logical examination of the way PHP is advertised to function, not
transitory benchmarks.


Paul M. Foster

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