Using preg_replace_callback with external class

Question

I have a question for you!

Normally, if you call a callback function within an OOP context you have to use array(&$this, 'callback_function')

That's what I figured out.

But now I want to call a callback in an external class, due to having to much callback_functions. I want to give them an own class for structure reasons.

I thought: "Ok, make an instance of this class and pass it instead of $this."

So I tried it with array($cb, 'callback_function') and array($this->cb, 'callback_function') but it won't work.

What am I doing wrong?

Thanks for your help!

Edit:

In my basic class I have:

    function __construct()
    {
        // some other vars here

        $this->cb = new Callback();
    }

And calling it with:

$newline = preg_replace_callback("/(^#+) (.*)/", array(&$this->cb, 'callback_heading'), $newline);

And in my callback class I have:

class Callback
{
    function __construct()
    {
        $this->list = array("num" => 0, "dot" => 0, "normal" => 0);
        $this->td = array("strike" => false, "bold" => false, "italic" => false, "underline" => false, "code" => false);
    }

    public function callback_heading($parameter)
    {
        $hashs = strlen($parameter[1]);
        $hashs++;
        if($hashs > 6)
            $hashs = 6;

        return "<h".$hashs."><span class=\'indented\'>".$parameter[1]."</span><strong>".$parameter[2]."</strong></h".$hashs.">";
    }

Those examples look like they should work. Post your code.

Jon
– Jon

2011-10-25 19:18:22 +00:00
Commented Oct 25, 2011 at 19:18 — Jon
– Jon, Commented Oct 25, 2011 at 19:18

hakre · Accepted Answer · 2011-10-26 15:30:19Z

First a comment:

Normally, if you call a callback function within an OOP context you have to use array(&$this, 'callback_function')

No, normally (these days) it's array($this, 'callback_function') - without the &.

Then, instead of $this you can put any variable that's representing an object:

$obj = $this;
$callback = array($obj, 'method');

or

class That
{
   function method() {...}
}

$obj = new That;
$callback = array($obj, 'method');

This just works, see the documentation of the callback pseudo type in the PHP Manual.

More similar to the code fragments of your question:

class Callback
{
    function __construct()
    {
        $this->list = array("num" => 0, "dot" => 0, "normal" => 0);
        $this->td = array("strike" => false, "bold" => false, "italic" => false, "underline" => false, "code" => false);
    }

    public function callback_heading($parameter)
    {
        $hashs = min(6, 1+strlen($parameter[1]));

        return sprintf("<h%d><span class=\'indented\'>%s</span><strong>%s</strong></h%d>", $hashs, parameter[1], $parameter[2], $hashs);
    }
}

class Basic 
{
    /** @var Callback */
    private $cb;
    function __construct()
    {
        // some other vars here
        $obj = new Callback();
        $this->cb = array($obj, 'callback_heading');
    }
    function replace($subject)
    {
        ...
        $result = preg_replace_callback($pattern, $this->cb, $subject);
    }
}

$basic = new Basic;
$string = '123, test.';
$replaced = $basic->replace($string);

Jeah I thought so, too. I used the reference for "security" due to php often does strange stuff
@zcei: If you have the feeling that PHP does strange stuff, always double check the manual and ensure you're doing everything right instead of guessing. Otherwise PHP will indeed do strange stuff.
hmh, I did, but did not find much about preg_replace_callback with classes. In the end it was due to the reference ampersand... Never trust sites found with google :>
With local vars like $obj as you mentioned it works. But why can't I use a member var $this->obj ? I always get that there is no callback.
@zcei: That works as well, however, ensure that the propery (class variable) already is a callback when you pass it to preg_replace_callback. I'll update the answer based on the code fragment of your question.

jchook · Accepted Answer · 2011-10-25 19:28:30Z

1

Say your external class looks like this

<?php
class ExternalClass {
    function callback() {
        // do something here
    }
}

If your callback function makes no reference to $this, you can call it statically like so:

preg_replace_callback($pattern, 'ExternalClass::callback', $subject);

Otherwise, your method should work in theory.

preg_replace_callback($pattern, array(new ExternalClass, 'callback'), $subject);

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