从类中静态调用实例方法

Question

According to one of the man pages http://www.php.net/manual/en/language.oop5.static.php :

Calling non-static methods statically generates an E_STRICT level warning.

But, this doesn't seem to be the case when the call is made from inside the class:

error_reporting(-1);

class Test {
    private $id;
    function __construct($id) { $this->id = $id; }
    function id() { return $this->id; }

    function __toString() {
        return Test::id()
             . self::id()
             . static::id()
             . static::id()
             . call_user_func('Test::id')
             . call_user_func(array('Test', 'id'));
    }
}
$a = new Test('a');
$b = new Test('b');


echo "$a $b $a"; # aaaaaa bbbbbb aaaaaa
var_dump(error_get_last()); # NULL

Testing with php 5.4

DEMO: http://codepad.viper-7.com/IKp9iX

I believe I've demonstrated:

• No E_STRICT warning is generated
• That php magically corrects the static method call to an instance method call(accessing the instance variable id proves this).

edit- I'd like to add that inserting debug_backtrace() into the __toString call yields a call "type" of ->, which means "method call".

Is this a bug, or a documented feature?

Answer 1

I'd say it's a semi-documented feature:

In non-static contexts, the called class will be the class of the object instance. Since $this-> will try to call private methods from the same scope, using static:: may give different results. Another difference is that static:: can only refer to static properties.

In other words (as I understood), it can be used to implement late static binding: using self::id() and static::id() may give different results if you call them in some class that extends your Test.