How is a PDO result set stored

I've been studying PHP for 2 months now as my first scripting language. For most of my problems i can easily find an answer online, but there's something about PDO that i can't seem to understand.

In order to retrieve data from a database I instantiate a new object of the PDO class and call the PDO::query() method on it. This returns a PDOStatement object which carries the result set from the SQL query. Here's where the problem starts. I can't seem to understand how and where the data from the result set is stored.

In the PHP Manual i learned to display the returned rows by iterating over the PDOStatement object with a foreach loop. However, the PHP manual clearly states that if an object is converted to an array, the result is an array whose elements are the object's properties . The PDOStatement only has one property - $queryString - containing the issued query string. So... where are the query results stored? And why can I reach them through an array with a foreach loop, but not outside of it?

// Instantiate new PDO object to establish a new connection with MySQL database
$db = new PDO('mysql:dbhost=localhost;dbname=world', 'root', 'secret');

// Execute SQL query - Returns a PDOStatement object
$result = $db->query("SELECT Name, Continent, Population FROM Country");


// Result set can be accessed with a foreach loop iterating over the PDOStatement object
foreach ($result as $row) {
    echo "$row[Name] - $row[Continent] - $row[Population] <br />";
}

// Outside the foreach loop, $result cannot be accessed this way.
// This produces 'Cannot use object of type PDOStatement as array'
echo $result[0]['Name'];

---

The PDOStatement class implements the Iterator interface, which lets its objects be iterated through.

Iterator extends Traversable {
    /* Methods */
    abstract public mixed current ( void )
    abstract public scalar key ( void )
    abstract public void next ( void )
    abstract public void rewind ( void )
    abstract public boolean valid ( void )
}

---

For an object that implements the Iterator interface,

foreach($result as $row) {
    // Code
}

is equivalent to

for ($result->rewind(); $result->valid(); $result->next()) {
    $row = $result->current();
    // Code
}

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