php method argument type hinting with question mark (?type)

Just a note to add to the previous answers - it must be
either null or have a value in the specified type i.e. - you
cannot just omit it - have a look at an example:

class="lang-php prettyprint-override">class TestClass {
public
function fetch(?array $extensions)
{
//...

}
}


Now if you
call

(new
            TestClass)->fetch();

this will
throw

ArgumentCountError : Too few arguments to function fetch()
...

To make it work without
passing array of $extensions you'd have to call it with
null as
argument

(new
            TestClass)->fetch(null);

It
works best in the situations, where you are passing argument initially set to
null to another method for processing
i.e.

class TestClass {
 public function
            fetch(array $extensions = null)
 {
 //...

            $this->filter($extensions);
 }
 private function filter(?array
            $extensions)
 {
 //...

            }
}

Now you can call
the fetch method without the
argument

(new
            TestClass)->fetch();