Question

I have a php class Assets. Within Assets there are a variety of public functions which handle assets (caching, minifying, combining…). One of the public functions contains a secondary function which is required to perform a preg_replace_callback(). This inner function needs to access one of the other public functions but I am having trouble calling the other functions.

Here is the setup:

class Assets
{

    public function img($file)
    {

        $image['location'] = $this->image_dir.$file;
        $image['content'] = file_get_contents($image['location']);
        $image['hash'] = md5($image['content']);
        $image['fileInfo'] = pathinfo($image['location']);

        return $this->cache('img',$image);

    }

    public function css($content)
    {

        . . .

        function parseCSS($matched){

            return $this->img($matched); // THIS LINE NEEDS TO REFERENCE function img()

        }

        $mend = preg_replace_callback(
            '#\<parse\>(.+?)\<\/parse\>#i',
            'parseCSS',
            $this->combined_css
        );

        . . .

    }

}

Here’s what I have tried:

$this->img($matched)

Error: Using $this when not in object context – Refers to $this->
inside of parseCSS()

Assets::img($matched)

Error: Using $this when not in object context – Refers to $this->
inside of img()

So, how can I access a public function with $this from within an inner function?

Answer 1

This would be more appropriate:

public function css($content)
{
    //. . .
    $mend = preg_replace_callback(
        '#\<parse\>(.+?)\<\/parse\>#i',
        array($this, 'parseCSS'),
        $this->combined_css
    );
    //. . .
}

public function parseCSS($matched){
    return $this->img($matched); // THIS LINE NEEDS TO REFERENCE function img()
}

Your original approach causes parseCSS to be defined every time css is called — which will probably result in a fatal error were you to ever call css twice. All questions of scope are also much more straightforward in my revised example. In your original example, parseCSS is a function in the global scope, and not associated with your class.

Edit: Valid callback formulations are documented here: http://php.net/manual/en/language.types.callable.php

// Type 1: Simple callback
call_user_func('my_callback_function'); 

// Type 2: Static class method call
call_user_func(array('MyClass', 'myCallbackMethod')); 

// Type 3: Object method call
call_user_func(array($obj, 'myCallbackMethod'));

// Type 4: Static class method call (As of PHP 5.2.3)
call_user_func('MyClass::myCallbackMethod');

// Type 5: Relative static class method call (As of PHP 5.3.0)
call_user_func(array('B', 'parent::who')); // A

//Type 6: Closure
$double = function($a) {
    return $a * 2;
};

$new_numbers = array_map($double, $numbers);

A closure-based solution is also possible as of PHP 5.4 — this would actually be similar to what you originally intended.