<?php
	assert_options(ASSERT_ACTIVE, '1');
	assert_options(ASSERT_WARNING, '1');
	assert_options(ASSERT_QUIET_EVAL, '0');

	$AVAILABLE_LANGS = array('az' => 'az', 'ru' => 'ru', 'en' => 'en'); # as per RFC 1766

	function func($predicate)
	{
		do {
			$freeflag = null;
			if (call_user_func($predicate, $freeflag) === FALSE)
				break;
			assert('!is_null($freeflag)');
		} while (0);
	}

	class foo
	{
		function foo_method(&$freeflag)
		{
			$retval = (bool) rand() % 2;
			if ($retval)
				$freeflag = 1;

			return $retval;
		}
	}

	$foo_instance = new foo;
	func(array($foo_instance, 'foo_method'));
?>

D:\>c:\php\php-cli haha.php

Warning: Assertion "!is_null($freeflag)" failed in haha.php on line 14

It occurs *always* no matter what foo_method() returns, as if asserts() are happening asynchronously.

If I instead change func() to
	function func($predicate)
	{
		$freeflag = null;
		if (call_user_func($predicate, $freeflag) === TRUE)
		    assert('!is_null($freeflag)');
	}

The assertion doesn't fail. (because it's NOTREACHED?)