php - array map using public function callback within class

Question

class something{   
    public function add_val( $val ){
    $array = array();
    foreach( $val as $value ) {
        $array[] = static::$post[${$value}];
    }
    return $array;
    }
    pulblic function somethingelse(){
       .... 
       ....
       $optionsArray['value'] = array_map( 'add_val', array_chunk( $drop_val, count( $optionsArray['heading_x'] ) ) );
       ....
       ....
    }
}

how can i call the add_val method within the other using array_map()??

Answer 1

Use an array that contains the object, and the method name:

$optionsArray['value'] = array_map(array($this, 'add_val'), array_chunk($drop_val, count($optionsArray['heading_x'])));

You do the same for most other functions that take in callbacks as parameters, like array_walk(), call_user_func(), call_user_func_array(), and so on.

How does it work? Well, if you pass an array to the callback parameter, PHP does something similar to this (for array_map()):

if (is_array($callback)) {         // array($this, 'add_val')
    if (is_object($callback[0])) {
        $object = $callback[0];    // The object ($this)
        $method = $callback[1];    // The object method name ('add_val')

        foreach ($array as &$v) {
            // This is how you call a variable object method in PHP
            // You end up doing something like $this->add_val($v);
            $v = $object->$method($v);
        }
    }
}

// ...

return $array;

Here you can see that PHP just loops through your array, calling the method on each value. Nothing complicated to it; again just basic object-oriented code.

This may or may not be how PHP does it internally, but conceptually it's the same.