An implementation of is_ref in PHP

is_ref.php

<?php
/**
 * This is a hacky is_ref function.
 * Determines whether a variable is a reference or not
 * by using var_dump on its symbol table and
 * checking whether it has '&' before its value or not.
 * @param  array   $defined_vars should send get_defined_vars() to this. enforced.
 * @param  mixed  $var          any variable, should be a variable and not a expression
 * @return boolean               
 */
function _is_ref($defined_vars=[],$var)
{
	$t=&debug_backtrace()[0];
	preg_match("/".__FUNCTION__."\(\s*get_defined_vars\s*\(\s*\)\s*,\s*\\$(.*?)\)/i", file($t['file'])[$t['line']-1],$varname);
	if ($varname)
		$varname=$varname[1];
	else
	{
		trigger_error("You need to provide two arguments to '".__FUNCTION__.
		"', namely get_defined_vars() and a variable");	
		return false; //an expression is not a reference
	}
	foreach ($defined_vars as $k=>$v)
		if ($k!==$varname)
			unset($defined_vars[$k]);
	ob_start();
	var_dump($defined_vars);
	$dump=ob_get_clean();
	if (($r=strpos($dump,"=>\n  &"))===false)
		return false;
	else 
	{
		if ($r>=17+strlen($varname) /*array(_) {\n  ["_"]*/
			and $r<20+strlen($varname))
		return true;
	}
	return false;
}