Question

The question is if a database connection should be passed in by reference or by value?

For me I’m specifically questioning a PHP to MySQL connection, but I think it applies to all databases.

I have heard that in PHP when you pass a variable to a function or object, that it is copied in memory and therefore uses twice as much memory immediately. I have also heard that it’s only copied once changes have been made to the value (such as a key being added/removed from an array).

In a database connection, I would think it’s being changed within the function as the query could change things like the last insert id or num rows. (I guess this is another question: are things like num rows and insert id stored within the connection or an actual call is made back to the database?)

So, does it matter memory or speed wise if the connection is passed by reference or value? Does it make a difference PHP 4 vs 5?

// $connection is resource function DoSomething1(&$connection) { ... } function DoSomething2($connection) { ... } 

Answer 1

A PHP resource is a special type that already is a reference in itself. Passing it by value or explicitly by reference won’t make a difference (ie, it’s still a reference). You can check this for yourself under PHP4:

function get_connection() {   $test = mysql_connect('localhost', 'user', 'password');   mysql_select_db('db');   return $test; }  $conn1 = get_connection(); $conn2 = get_connection(); // 'copied' resource under PHP4  $query = 'INSERT INTO test_table (id, field) VALUES ('', 'test')'; mysql_query($query, $conn1); print mysql_insert_id($conn1).'<br />'; // prints 1  mysql_query($query, $conn2); print mysql_insert_id($conn2).'<br />'; // prints 2  print mysql_insert_id($conn1); // prints 2, would print 1 if this was not a reference