Question

Since PHP treats them equally in string operations and output, I would like to know what is the best practice, to assign/concatenate a null value or an empty string:

$lang = 'lang';
$suffix = null;
$lang .= $suffix;

or

$desc = 'name';
$suffix = '';
$desc .= $suffix;

This can also be the case for inline conditions:

<div class="item<?= $is_selected ? ' selected' : null ?>"></div>

or

<div class="item<?= $is_selected ? ' selected' : '' ?>"></div>

I know it won’t affect the overall performance, but could it compare to using double or single quotes?

Answer 1

> php --version
PHP 5.3.12 with Suhosin-Patch (cli) (built: May  9 2012 11:44:31) 
Copyright (c) 1997-2012 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2012 Zend Technologies
    with Suhosin v0.9.33, Copyright (c) 2007-2012, by SektionEins GmbH

php > $start = microtime(true); for( $i = 0; $i < 1000000; ++$i ) { $str = 'foo'; $str .= null; } printf('%.5f', microtime(true) - $start);
0.15258
php > $start = microtime(true); for( $i = 0; $i < 1000000; ++$i ) { $str = 'foo'; $str .= ''; } printf('%.5f', microtime(true) - $start);
0.11397

Ran this a few times, and got very similar results every time.

Conclusion:

• Appending an empty string to a string is very slightly faster than appending null to an empty string.
• Unless you are doing this inside a loop with billions of iterations, it doesn’t matter from a performance standpoint, so use the one that makes better semantic sense.