How to call a protected method in php?

问题:

here is the class structure. I want Observer:callme() to be callable from Children too.

class Observer
{
    protected callme()
    {
    }
}

class Parent extends Observer
{
    function createChild()
    {
        $this->callme(); // this is OK
        return new Child ($this);
    }
}

class Child
{
    private $this myParent;
    public function __constructor ($myParent)
    {
        $this->myParent = $myParent;
    }

    public function __destroy()
    {
        $this->myParent->callme(); // FAIL!
    }
}

so how to make FAIL work? (without making it public, because its only for used inside "Parent" and its "Children")

回答1:

protected means that you can call that method only from the same class and from subclasses. What you want to do is not possible. The protected keyword would be pointless if you could call these methods from everywhere.

In C++ there is the friend keyword to achieve what you want: you could define Child as friend of Observer (this has to be done from within Observer), and then you can call all methods in Observer (including private and protected) from within methods of Child. But such a keyword does not exist for PHP.

回答2:

The problem is that a protected method is only accessed from the same class or the class children. What you can do is extend your Child class from Parent, like this:

class Child extends Parent
{
    public function __constructor ()
    {
        parent::__constructor();
    }

    public function __destroy()
    {
        $this->callme(); // Should work!
    }
}

Or just change the method to public.

And, btw, is this code some kind of real code that you will use? That constructor receiving the parent object seems to be so wrong. What are you trying to accomplish?

回答3:

My comment on your question explains why it doesn't work. This answer shows a way to accomplish what you asked based upon your clarification that MyChild should not extend MyParent.

This is a hack example that makes it work by exploiting the fact that php doesn't care if you call protected methods on other instances than yourself as long as you share the ancestor of the protected method.

I had to change the code some to make it valid php. __constructor is not the name of a php constructor.

hacky.php

<?php

class Observer
{
    protected function callme()
    {
        echo 'I was called from ' . get_called_class(), PHP_EOL;
    }
}

class MyParent extends Observer
{
    public function createMyChild()
    {
        $this->callme(); // this is OK
        return new MyChild ($this);
    }
}

class MyChild extends Observer // hackey extends
{
    private $myMyParent;
    public function __construct($myMyParent)
    {
        $this->myMyParent = $myMyParent;
        $this->myMyParent->callme();
    }
}

$p = new MyParent;
$c = $p->createMyChild();

Result:

$ php hacky.php
I was called from MyParent
I was called from MyParent

回答4:

I think I found the solution:

class Parent extends Observer
{
    function createChild()
    {
        $this->callme(); // this is OK
        return new Child (function() { $this->callme(); });
    }
}

class Child
{
    private $gatewayFunction;
    public function __constructor (Closure $gatewayFunction)
    {
        $this->gatewayFunction = $gatewayFunction;
    }

    public function __destroy()
    {
        $this->gatewayFunction->__invoke();
    }
}

Who is going to crap himself? :)