How to override private method from a library class

Question

Given are the following classes with class A coming from an external library so that I can not change it:

class A {
    public function test () {
        $this->privateMethod();
    }
    private function privateMethod () {
        echo('A');
    }
}

class B extends A {
    private function privateMethod () {
        echo('B');
    }
}

$b = new B();
$b->test();

This results in A being printed out by A::privateMethod instead of B from B::privateMethod, because the latter is not visible to A::test as explained here.

How else can I modify the behavior of this private library method in the cleanest possible way (e.g. without code duplication from copying the whole class and changing it)?

There are several solutions to this, it might be useful to know which library you are using, assuming it is open source. — Flosculus, May 21 '15 at 14:55
Yes, [it is](https://github.com/jjriv/emogrifier). I need to change `getCssFromAllStyleNodes`. — hielsnoppe, May 21 '15 at 14:59

Daan · Answer 1 · 2017-02-16T13:44:01.140

3

That is because private is only in the scope of the class itself. I you had used protected you would've overridden the function, because a protected method means it's available for child classes.

edited Feb 16 '17 at 13:44

answered May 21 '15 at 14:54

Daan

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1

I know why it doesn't work, but I am looking for a different way to achieve what I stated in the question. – hielsnoppe May 21 '15 at 14:57
2

I don't think that answers the question. The OP says it's a library so he cannot change the access modifiers. – marekful May 21 '15 at 14:59

score 2 · Answer 2 · answered May 21 '15 at 15:12

You can change accessibility of a class method using ReflectionMethod::setAccessible():

$myEmogrifier = new \Pelago\Emogrifier;
$reflectedMethod = new ReflectionMethod($myEmogrifier, 'getCssFromAllStyleNodes');
$reflectedMethod->setAccessible(true);
$argument = new \DOMXpath(new \DOMDocument);
$returnValue = $reflectedMethod->invoke($myEmogrifier, $argument);

Take into account that this code will be 'fragile', since the author of the library will not take into account that a user of the library is relying on the result of a private function. It may be better to simply duplicate the function's code yourself than messing with the library itself.

Flosculus · Accepted Answer · 2015-05-21T15:24:38.253

You can manipulate the behaviour indirectly. This is the snippet you are interested in.

$allCss = $this->css;

if ($this->isStyleBlocksParsingEnabled) {
    $allCss .= $this->getCssFromAllStyleNodes($xpath);
}

Looking at the class setters, you can call disableStyleBlocksParsing to prevent the function being called.

The $allCss variable is taken straight from $this->css, which is only modified by the setCss method.

So you have two choices:

Extend the class, make isStyleBlocksParsingEnabled false and immutable, then override the setCss method to do what you wanted getCssFromAllStyleNodes to do.
Call disableStyleBlocksParsing and and call setCss with preprocessed text.

Here is an example of the first option:

class MyEmogrifier extends Emogrifier
{
    public function __construct($html = '', $css = '')
    {
        parent::__construct($html, $css);

        $this->disableStyleBlocksParsing();
    }

    public function setCss($css)
    {
        // Preprocess CSS here.

        parent::setCss($css);
    }
}

So there is no shotgun surgery, or reflection needed.

To be honest though. I would feel much less inclined to even use a library as concrete as this one. I use protected for nearly all of my would be private methods.

score 0 · Answer 4 · answered May 21 '15 at 15:17

You can change hardcode visibility of property via ReflectionClass::setAccessible this is a part of ReflectionClass.

Sets a property to be accessible. For example, it may allow protected and private properties to be accessed.

It is dangerous but in some cases you can use it.

How to override private method from a library class

4 Answers4