<?php

class Test implements ArrayAccess 
{
    public function offsetSet($offset, $value) {
        var_dump(__METHOD__, $value);
    }
    public function offsetExists($var) {
        var_dump(__METHOD__, $var);
    }
    public function offsetUnset($var) {
        var_dump(__METHOD__);
    }
    public function offsetGet($var) {
        var_dump(__METHOD__, $var);
        return "value";
    }
}

$test = new Test;
var_dump(isset($test['asasas']));