So, that means that assertions are so fast, that disabling them doesn't affect script performance. Agree?
But if you change your code in this way:
assert(is_numeric($i));
=>
assert("is_numeric($i)");
you'll get expected results.

Well, assertions are not really fast - actually, they are a bottle neck. I modified my previous script. Look at this:

-----------------------------------------------------------------------------
<?php

$doAsserts = array(true, false);

foreach ($doAsserts as $doAssert)
{
	ini_set('assert.active', $doAssert);		// Turn assertions on/off
	$startTime = microtime(true);

	for ($i = -500000; $i < 500000; $i++)
	{
		$result = $i * $i;		// just to have
		assert($result >= 0);
	}

	$endTime = microtime(1);
	$time = $endTime - $startTime;
	print "Elapsed time: $time\r\n";
}

?>
-----------------------------------------------------------------------------

Running this script, I get:

Elapsed time: 1.6357040405273
Elapsed time: 1.6131460666656

Now I comment the line "assert($result >= 0);" so that the script looks like this:

-----------------------------------------------------------------------------
<?php

$doAsserts = array(true, false);

foreach ($doAsserts as $doAssert)
{
	ini_set('assert.active', $doAssert);		// Turn assertions on/off
	$startTime = microtime(true);

	for ($i = -500000; $i < 500000; $i++)
	{
		$result = $i * $i;		// just to have
		//assert($result >= 0);
	}

	$endTime = microtime(1);
	$time = $endTime - $startTime;
	print "Elapsed time: $time\r\n";
}

?>
-----------------------------------------------------------------------------

When I run the script again, I get:

Elapsed time: 0.87688493728638
Elapsed time: 0.87343096733093

As you can see from this, about 50% of the execution time is spent in the assertion! This would be still acceptable, if I could simply disable assertions. Well, I can - by ini_set('assert.active', true); - however, this only disables assertions without affecting the performance at all. When disabling assertions, any assertion should rather be considered as not existant (like a comment).
I hope this can be fixed in a future PHP version! Thanks.

In the last paragraph, I meant

ini_set('assert.active', false);

of course. Sorry for the inconvenience.

Best regards
Andr? Meyer
labeltools GmbH

>Well, assertions are not really fast - actually, they are a 
>bottle neck.
you're probably kidding me.

>As you can see from this, about 50% of the execution time 
>is spent in the assertion!
yes.
500 thousands of function calls took about a second.
is it a bottle neck?
you're real-life application calls assert() billions of times?

again, I don't see any performance problem here.

change "assert" in your code to something else and try again - you'll see the very same results, even worse.
function call is rather expensive operation (even if the function just returns true).