When you declare one variable, the initial type is null, but the type can be changed by assign statement.

global $my_var;
echo gettype($my_var);

$my_var = new stdClass();
$my_var->name = ‘test‘;
$my_var->city = ‘china‘;

//$my_var[‘weather‘]= ‘cold‘;

echo gettype($my_var);
var_dump($my_var);

[PHP] small example to show dynamic type change