Problems with attributes in php object-oriented

class play{

<code>private $message = null;
public function __construct(){

}
public function callback(event $event){
    $this->message = $event->click();
    ...
}</code>

}

Please tell me why you need to add event before $event in public function callback(event $event)? What does the event here do?

Thank you

Reply content:

class play{

<code>private $message = null;
public function __construct(){

}
public function callback(event $event){
    $this->message = $event->click();
    ...
}</code>

}

Please tell me why you need to add event before $event in public function callback(event $event)? What does the event here do?

Thank you

Type declaration: The formal parameter $event must be an instance of (class/interface) event or an instance of a subclass of event (or a class that implements the event interface)

Thank you, that is the parameter type restriction of PHP function. That is, when you call $play->callback($event), if $event is not of type event, an error will be reported. The following picture is a table of the types that PHPfunction parameters can be set.

Strictly limit input types.