[Objects] functions within functions

[gavshouse]

Hi im trying to build a replacement for a standard mysql query to replace it with my custom class which i intend to make with memcache support, the problems im having are due to building my query, since the data is not set im sending my query information in an array. i need to filter the parameters though and build a sprinft query, therefore im using array_map so i can apply a function to each parameter but my problem is that im also using the mysqli class

I tried to do this

                  array_map($this->mysqli->real_escape_string, $query['parameters']);

but php didnt like that either, i also tried many ideas. i then thought about creating a function then within the function sorting the issue. This then created another problem of how do i send my $this or just $this->mysqli to this function

                   //ERROR IS HERE !
			function _escape($value){
				return $this->mysqli->real_escape_string($value);
			}

		//apply functions to each parameter
		$query['parameters'] = array_map("_escape", $query['parameters']);

FULL CODE

<?php
	class mysqli_cache{
		#Objects
		public $mysqli;
		private $memcache;

	public function __construct(){
		//open memcache connection
	}		
	public function __destroy(){
		//close memcache			
		//if mysqli is open close it
	}		
	public function query($query, $cache_time){
		if(!is_object($this->mysqli)){
			$this->mysqli = new mysqli('localhost', 'root', 'letmein', 'test');
		}			

                    //ERROR IS HERE !
		function _escape($value){
			return $this->mysqli->real_escape_string($value);
		}

		//apply functions to each parameter
		$query['parameters'] = array_map("_escape", $query['parameters']);

		foreach($query['parameters'] as $value){//now the parameters are safe add them to the query
			array_push($query['sql'], $value);
		}			

		$query = call_user_func_array('sprintf', $query['sql']);
		die($query);
	}
}

$cache = new mysqli_cache();	
$query = array('sql' => array(), 'parameters' => array());
$query['sql'][0] = "SELECT * FROM test WHERE test='%u' LIMIT 1";
$query['parameters'][0] = "1";

$result = $cache->query($query, 60);
?>