Is assigning variable with Scope Resolution Operator(::) same as $this->variable?

Question

Just curious.

if I assign self::$session = $reg->get('session'); in a __construct class, can the variable be used as the class' properties just like $this->session = $reg->get('session'); ?

I have no idea how to test this. The only way I could test this is to make my entire framework in ruin by changing them all.

Answer 1

Just tried a bit around what is possible on the PHP shell ( php -a ).

php > class a { public $b; function __construct () { self::$b = 10; } }
php > $o = new a;
PHP Fatal error:  Access to undeclared static property: a::$b in php shell code on line 1

php > class a { public static $b; function __construct () { $this->b = 10; } }
php > $o = new a;
php > print $o->b;
10
php > print a::$b;
php > // outputs nothing (is still NULL)

php > class a { public static $b; function __construct () { self::$b = 10; } }
php > $o = new a;
php > print $o->b;
PHP Notice:  Undefined property: a::$b in php shell code on line 1

php > // doesn't print a value (basically NULL)

What we find out

• You cannot assign a non-static property like a static property (with self::... ).
• You can assign a static property like a non-static property. But it creates a new implicit non-static public property instead of changing the value of the static property.
• You cannot access a static property like a non-static property.

Conclusion

No, you cannot switch between static and non-static accesses and writes.

Answer 2

Before I start this, you could test this easily with an online codepad tool as well, but I felt it might be better to actually explain what's going on.

Let's assume you have this class, based on what you have described:

class MyClass
{
    private static $session;

    public function __construct($reg)
    {
        self::$session = $reg->get('session');
    }
}

The expression self::$session references a class variable which is shared amongst all instances of MyClass .

Let's change the class to the following:

class MyClass
{
    private $session;

    public function __construct($reg)
    {
        $this->session = $reg->get('session');
    }
}

Now, the expression $this->session references an instance variable, which is not shared with any other instance of MyClass .

Because of this difference, they can't be used interchangeably and you will have to make a decision based on your functional design.