Description:
------------
I found this issue when testing a Magento 1.9 application.

Using array elements to call a method on an object doesn't work in php7, but used to work in php5. I made a simplified example in the test script below.

Test script:
---------------
<?php

class Item {
    public function save()
    {
        echo 'saved';
    }
}

$callback = [new Item(), 'save'];

// This works on both php5 and php7
$method = $callback[1];
$callback[0]->$method();

// This works on php5 only
$callback[0]->$callback[1]();

Expected result:
----------------
Expected "savedsaved" output.

Actual result:
--------------
saved
Notice: Array to string conversion in /var/www/test/array_function.php on line 15

Notice: Undefined property: Item::$Array in /var/www/test/array_function.php on line 15

Fatal error: Function name must be a string in /var/www/test/array_function.php on line 15