A bit weird and unintuitive coalesce behaviour, so watch out when using it!

 

$coalesce = true === false ?? 'no';
var_dump($coalesce); // false - huh?

so it seems that it works only for null :/

 

$coalesce = null == false ?? 'no'; 
var_dump($coalesce); // true

so the only valid and straight forward example comes from php.net:

 

$coalesce = $_GET['something'] ?? 'default'; 
var_dump($coalesce); // default

 

$username = !isset($_GET['something']) ?? 'wtf';    
var_dump($username); // true

 

$_POST['second'] = 'chain';
$nc = $_GET['first'] ?? $_POST['second'] ?? $_REQUEST['third'] ?? 'wtf';
var_dump($nc); // chain

 

$nc = isset($_GET['something']) ?? 'wtf';
var_dump($nc); // false

if you need to install PHP7 check out this article