A-B Test (call it benchmark) to show that php evaluates operands from left to right and does not at all evaluate operands, if the condition cannot be met anymore

abtest.php

define('ITERATIONS', 1000000);
define('ROUNDS', 10);

function original($singular, $args = null) {
	if ($args === null) {
		return true;
	} else {
		return false;
	}
}

function modified($singular, $args = null) {
	if ($args === null && func_num_args() < 2) { // this is the proposed solution. it adds (almost absolutely) no time to the check if $args === null
//	if ($args === null && call_user_func(function($a) { for($i = 0; $i < $a; $i++); }, 128)) { // this is just to proof that this never happens if $args === null
		return true;
	} else {
		return false;
	}
}

function modified2($singular, $args = null) {
	if (func_num_args() < 2) { // this is sufficient because of inconsistent php behaviour, AGAIN! see test below... it is (relatively) slow in every case though
		return true;
	} else {
		return false;
	}
}

$tests = array(
	'original_times' => array(
		'function' => 'original',
		'params' => array('Test'),
		'text' => 'Original  ($args not set) ',
	),
	'original_null_times' => array(
		'function' => 'original',
		'params' => array('Test', null),
		'text' => 'Original  ($args === null)',
	),
	'original_not_null_times' => array(
		'function' => 'original',
		'params' => array('Test', false),
		'text' => 'Original  ($args !== null)',
	),

	'modified_times' => array(
		'function' => 'modified',
		'params' => array('Test'),
		'text' => 'Modified  ($args not set) ',
	),
	'modified_null_times' => array(
		'function' => 'modified',
		'params' => array('Test', null),
		'text' => 'Modified  ($args === null)',
	),
	'modified_not_null_times' => array(
		'function' => 'modified',
		'params' => array('Test', false),
		'text' => 'Modified  ($args !== null)',
	),

	'modified2_times' => array(
		'function' => 'modified2',
		'params' => array('Test'),
		'text' => 'Modified2 ($args not set) ',
	),
	'modified2_null_times' => array(
		'function' => 'modified2',
		'params' => array('Test', null),
		'text' => 'Modified2 ($args === null)',
	),
	'modified2_not_null_times' => array(
		'function' => 'modified2',
		'params' => array('Test', false),
		'text' => 'Modified2 ($args !== null)',
	),
);

foreach($tests as $key => $test) {
	$$key = array();
}

for($r = ROUNDS; $r > 0; $r--) {
	foreach($tests as $key => $test) {
		$start_time = microtime(true);
		$c = ITERATIONS;
		$function = $test['function']; // do not distract the benchmark
		$params = $test['params']; // my these array lookups, use local vars instead
		while($c--) call_user_func_array($function, $params);
		array_push($$key, microtime(true) - $start_time);
	}
}

echo sprintf('Times for %s iterations in %s rounds on php-%s:%s', ITERATIONS, ROUNDS, phpversion(), PHP_EOL);
$r = 0;
foreach($tests as $key => $test) {
	if($r++ % 3 == 0) echo PHP_EOL;
	sort($$key);
//	echo sprintf('%s%s%s', $test['text'], implode(', ', $$key), PHP_EOL);
	echo sprintf('%s: %ss avg%s', $test['text'], array_sum($$key) / count($$key), PHP_EOL);
}

/* Another php-inconsistency that I came accross when testing this,
 * the change reads func_num_args() < 2 instead of the proposed func_num_args() < 3:
 * Default arguments are not shown in the func_get_args() and func_num_args() functions!
 */
function args_test($single, $args = null) { var_dump(func_get_args(), func_num_args()); }
echo PHP_EOL;
echo 'args_test("Test"):' . PHP_EOL;
args_test('Test');
echo PHP_EOL;
echo 'args_test("Test", null):' . PHP_EOL;
args_test('Test', null);

/*
 RESULTS:

Times for 1000000 iterations in 10 rounds on php-5.5.14:

Original  ($args not set) : 0.53223054409027s avg
Original  ($args === null): 0.57213246822357s avg
Original  ($args !== null): 0.56663253307343s avg

Modified  ($args not set) : 0.58333339691162s avg
Modified  ($args === null): 0.62863585948944s avg
Modified  ($args !== null): 0.57763316631317s avg

Modified2 ($args not set) : 0.56753251552582s avg
Modified2 ($args === null): 0.60613462924957s avg
Modified2 ($args !== null): 0.60433461666107s avg

Times for 1000000 iterations in 10 rounds on php-5.4.30:
Original  ($args not set) : 0.57273278236389s avg
Original  ($args === null): 0.59973433017731s avg
Original  ($args !== null): 0.59833409786224s avg

Modified  ($args not set) : 0.63493618965149s avg
Modified  ($args === null): 0.65893802642822s avg
Modified  ($args !== null): 0.60833466053009s avg

Modified2 ($args not set) : 0.62743582725525s avg
Modified2 ($args === null): 0.65103728771210s avg
Modified2 ($args !== null): 0.65303740501404s avg

Times for 1000000 iterations in 10 rounds on php-5.3.28:
Original  ($args not set) : 0.67083833217621s avg
Original  ($args === null): 0.70034017562866s avg
Original  ($args !== null): 0.70163998603821s avg

Modified  ($args not set) : 0.76344385147095s avg
Modified  ($args === null): 0.79184517860413s avg
Modified  ($args !== null): 0.70774047374725s avg

Modified2 ($args not set) : 0.76374368667603s avg
Modified2 ($args === null): 0.78644495010376s avg
Modified2 ($args !== null): 0.78834505081177s avg

// This are the results for the long taking anonymous function instead of the func_num_args() call,
// to demonstrate that this function does not even execute if $args !== null:
Modified  ($args not set) : 1.878107380867s avg // extra slowed down
Modified  ($args === null): 1.9067091464996s avg // extra slowed down
Modified  ($args !== null): 0.71474087238312s avg // same as above

args_test("Test"):
array(1) {
  [0]=>
  string(4) "Test"
}
int(1)

args_test("Test", null):
array(2) {
  [0]=>
  string(4) "Test"
  [1]=>
  NULL
}
int(2)