打印$ GLOBALS私有静态属性未显示

Question

I am practicing the singleton pattern using several examples. My code so far:

class LimitedEditionBuggati {
    private $props = array(
                            'speed'     => 256,
                            'cylinders' => 18,
                            'color'     => 'metalic silver',
                            'hp'        => 1200,
                            'price'     => 5000000,
                            'vin'       => 'the one'
                           );
    private static $instance;

    private function __construct(){}

    public static function instance() {
        if( empty($instance) ) {
            return new LimitedEditionBuggati();
        }
        return self::$instance;
    }

    public function getProperty( $property ) {
        return $this->props[$property];
    }
}

$myCar = LimitedEditionBuggati::instance();

How come the private static $instance does not get printed using print_r( $GLOBALS )?

Answer 1

How come the private static $instance does not get printed using print_r( $GLOBALS )?

Even though static class variables are variables that exist once and only once - as it is similar with global variables - they are not globally visible through $GLOBALS because they are not global variables in PHP.

You can compare that with static variables inside a function (perhaps a better known concept for you):

function my_function()
{
    static $variable = 1;
}

my_function();
print_r($GLOBALS);

Even though the static variable $variable exists once and only once - similar to a global variable, it is just, that it is not visible in $GLOBALS.