<?php
$rp = new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::PRIMARY);
var_dump($rp->getMode());
$rp = new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::PRIMARY_PREFERRED);
var_dump($rp->getMode());
$rp = new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::SECONDARY);
var_dump($rp->getMode());
$rp = new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::SECONDARY_PREFERRED);
var_dump($rp->getMode());
$rp = new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::NEAREST);
var_dump($rp->getMode());
?>
The above example will output:
int(1)
int(5)
int(2)
int(6)
int(10)