Singleton in PHP

singleton.php

<?php

class Student
{
    protected static $instance;
    public function __construct($name = null)
    {
        $this->name = $name;
    }
    public static function instance()
    {
        if (static::$instance == null) {
            static::$instance = new static;
            return static::$instance;
        } else {
            return static::$instance;
        }
    }
}

//helper function
function getStudent()
{
    return Student::instance();
}

$studentSingleton = getStudent();
$studentSingleton1 = getStudent();
$student = new Student('Tamara');
$student1 = new Student('Teo');
$student2 = new Student('Tamara');

echo 'Singletons compared by value: ' . ($studentSingleton == $studentSingleton1 ? 'true' : 'false') . "\n";
echo 'Singletons compared by reference: ' . ($studentSingleton === $studentSingleton1 ? 'true' : 'false') . "\n";
echo 'Objects compared by value: ' . ($student == $student1 ? 'true' : 'false') . "\n";
echo 'Objects compared by reference: ' . ($student === $student1 ? 'true' : 'false') . "\n";
echo 'Objects compared by value: ' . ($student == $student2 ? 'true' : 'false') . "\n";
echo 'Objects compared by reference: ' . ($student === $student2 ? 'true' : 'false') . "\n";