Bitwise &= for multiple boolean checks

gistfile1.php

<?php

function op($d){
    return $d;
}

$ok = true;

$ok &= op(true);
$ok &= op(true);
$ok &= op(true);

var_dump((bool)$ok); // yields true because all op()s are true.

// another scenario

$ok = true;

$ok &= op(true);
$ok &= op(false);
$ok &= op(true);

var_dump((bool)$ok); // yields false because one of the op()s is false.