Description:
------------
I tried to access a private variable (an array) using $this->$error_type[$error_code], but PHP failed and gave me a notice about a non-existent offset. Using var_dump/print_r on $this->$error_type returned the desired array with all elements. I've double-checked everything and the only way I found to solve this was creating a local copy of the array.

Notice on the code:
- $this->db_error is an array with an offset called (INVALID_CONNECTION_STRING)
- The code was called via function __get()

Reproduce code:
---------------
<?php
$error_code = 'DB_INVALID_CONNECTION_STRING';
$temp_array = explode('_', $error_code, 2);
$error_type = (string) strtolower($temp_array[0]) . '_error'; // Value: db_error
$error_code = (string) $temp_array[1]; // Value: INVALID_CONNECTION_STRING

// ***
// *** This does not work
// ***

echo $this->$error_type[$error_code];

// ***
// *** This does work (local copy of the array)
// ***

$error_array = $this->$error_type;
echo $error_array[$error_code];
?>

Expected result:
----------------
Return an error-message from an array identified by its error-code

Actual result:
--------------
With the local copy it prints the correct value associated with the identifier $error_code

Without a local copy:
Notice: Undefined offset: 1 in C:\Path\To\Files\Errors.php on line 86

Notice: Undefined property: ErrorMessage::$d_error in C:\Path\To\Files\Errors.php on line 87

Notice: Undefined property: ErrorMessage::$d in C:\Path\To\Files\Errors.php on line 89

Notice: Undefined property: ErrorMessage::$d in C:\Path\To\Files\Errors.php on line 89