php – What is the autocasting (I do not know if that is how it is written) and how to use it?

I'm sorry if I was not clear or if it's a fierce question, I always see it in many places and I do not know what it is.

I have class: and

class and {
private group $ = [];
public service __construct () {
$ this-> group['Start'] = table (
& # 39; GET & # 39; => array (
& # 39; Home & # 39; => array (
& # 39; Method & # 39; => & # 39; ControllerHome @ index & # 39 ;,
& # 39; Connected & # 39; => true,
& # 39; Settings & # 39; => false
)
)
)
}

public function GET ($ g, $ function, $ saved, $ parameters) {
$ explode = explode (& # 39 ;, $ g);
if (array_key_exists ($ explode[0], $ this-> group)) {
if (! array_key_exists ($ explode[1], $ this-> group

explode[$Explode[$explode[0]]['GET'])) {
$ this-> group

explode[$Explode[$explode[0]]['GET']explode[$Explode[$explode[1]]= table (
& # 39; Method & # 39; => $ function,
& # 39; Connected & # 39; => $ registered,
& # 39; Settings & # 39; => $ parameters
)
// var_dump ($ this-> group);
$ t = new z (& # 39; a & # 39;);
returns $ t;
}
} else {
$ this-> group

explode[$Explode[$explode[0]]['GET'] = [];
$ this-> GET ($ g, $ function, $ connected, $ parameters);
}
}

Public function POST ($ g, $ function, $ saved, $ parameters) {
$ explode = explode (& # 39 ;, $ g);
if (array_key_exists ($ explode[0], $ this-> group)) {
if (! array_key_exists ($ explode[1], $ this-> group

explode[$Explode[$explode[0]]['GET'])) {
$ this-> group[$g]['GET']explode[$Explode[$explode[1]]= table (
& # 39; Method & # 39; => $ function,
& # 39; Connected & # 39; => $ registered,
& # 39; Settings & # 39; => $ parameters
)
var_dump ($ this-> group);
}
} else {
$ this-> group

explode[$Explode[$explode[0]]= [];
$ this-> x ($ g, $ function, $ saved, $ parameters);
}
}
}

just below the class z

class z {
public service __construct ($ test) {

}

public service r ($ message) {
return $ message;
}
}

What I want is to call the function of the other class (in the case r ()).

$ a = new and ();
$ a-> GET (k / home, ControllerHome @ index, true, false) -> r (& # 39;

Is there a specific name for this action? And how can I use it? Because I get the following error: Error: Calling member function r () on null in C: laragon www new_note_new index.php on line 70