Reference PHP object key as a function parameter

Question

This may not be possible, but it would be good to know either way.

I'm looking to use a method to run a process that's repeated in a custom class I wrote.

One of the function parameters, Target, needs to refer to an object key in $values, so in the snippet below, it relates to $value->Target.

public function format_array($post_id, $object, $values, Target, $meta_value) {
    $array = (array) $object;
    $feed_values = array();

    if ( !empty($array) ) {
        foreach ( $values as $value ) {
            $feed_values[] = $value->Target;
        }
    }

    unset($array);

    $db_values = get_post_meta( $post_id, $meta_value, true );

    $result = array_diff($feed_values, $db_values);

    if ( !empty($result) ) {
        $this->update_post_meta( $post_id, $meta_value, $feed_values );
    }
}

I know this code is currently broken...

Can this be done?

EDIT

Referring to $value->Target, where $value is the object example below, I'm trying to access 'Comment', so $value->comment:

object(stdClass)#411 (33) {
  ["Facilities"]=>
  object(stdClass)#413 (1) {
    ["FacilityInfo"]=>
    array(6) {
      [0]=>
      object(stdClass)#414 (4) {
        ["ID"]=>
        string(21) "xxxxx"
        ["PropertyID"]=>
        string(21) "xxxxx"
        ["Name"]=>
        string(5) "xxxxx"
        ["Comment"]=>
        string(9) "xxxxx"
      }
      [1]=>
      object(stdClass)#415 (4) {
        ["ID"]=>
        string(21) "xxxxx"
        ["PropertyID"]=>
        string(21) "xxxxx"
        ["Name"]=>
        string(15) "xxxxx"
        ["Comment"]=>
        string(20) "xxxxx"
      }
    }
  }
  ["Photos"]=>
  object(stdClass)#420 (1) {
    ["PhotoInfo"]=>
    array(5) {
      [0]=>
      object(stdClass)#421 (6) {
        ["ID"]=>
        string(21) "xxxxx"
        ["PropertyID"]=>
        string(21) "xxxxx"
        ["MainPhoto"]=>
        bool(true)
        ["Name"]=>
        string(8) "xxxxx"
        ["Type"]=>
        string(5) "Photo"
        ["PhotoUrl"]=>
        string(94) "xxxxxx"
      }
      [1]=>
      object(stdClass)#422 (6) {
        ["ID"]=>
        string(21) "xxxxx"
        ["PropertyID"]=>
        string(21) "xxxxx"
        ["MainPhoto"]=>
        bool(false)
        ["Name"]=>
        string(2) "xxxxx"
        ["Type"]=>
        string(5) "Photo"
        ["PhotoUrl"]=>
        string(94) "xxxxxxx"
      }
    }
  }
}

Example of how my working method currently looks, but I'd like to prevent having to reuse this for 3 different values:

$array = (array) $letmc->Facilities;
$comments = array();

if ( !empty($array) ) {
    foreach ( $letmc->Facilities->FacilityInfo as $Facility ) {
        $comments[] = $Facility->Comment;
    }
}

unset($array);

$property_comments = get_post_meta( $post_id, 'property_comments', true );

$result = array_diff($comments, $property_comments);

if ( !empty($result) ) {
    $this->update_post_meta( $post_id, 'property_comments', $comments );
}

---

$array = (array) $letmc->Photos;
$photos = array();

if ( !empty($array) ) {
    foreach ( $letmc->Photos->PhotoInfo as $Photo ) {
        $photos[] = $Photo->PhotoUrl;
    }
}

unset($array);

$property_photos = get_post_meta( $post_id, 'property_photos', true );

$result = array_diff($photos, $property_photos);

if ( !empty($result) ) {
    $this->update_post_meta( $post_id, 'property_photos', $photos );
}

Answer 1

Not entirely sure what your question is, but... like so?

function foo($obj, $property) {
    echo $obj->$property;
}

$bar = new stdClass;
$bar->baz = 42;

foo($bar, 'baz');

See variable variables in PHP.

Answer 2

AS CD001, suggested, you could use the magic method __get(). For instance, in one of the classes whose properties you are trying to access, you'd do this:

class Foo
{
   protected $prop; //property you wish to access outside of the class

   //magic method
   public function __get($val)
   {
      return isset($this->$val) ? $this->$val : '';
   }
}

Answer 3

Updated question makes this nice and clear :)

public function format_array($post_id, $object, $values, $target, $meta_value) {

    ...

    if ( !empty($array) ) {
        foreach ( $values as $value ) {
            $feed_values[] = $value->$target;
        }
    }

    ...
}

You may wish to check the $target exists first though:

public function format_array($post_id, $object, $values, $target, $meta_value) {

    ...

    if ( !empty($array) ) {
        foreach ( $values as $value ) {
            if(property_exists($value, $target) {
                $feed_values[] = $value->$target;
            }
        }
    }

    ...
}

Potential edit:

I think maybe we're looking at the wrong thing, if you want the obejct at the entry for FacilityInfo then you need to do it like this (no loops).

if ( !empty($array) ) {
    $feed_values[] = $values->$target;
}

or to check first:

if ( !empty($array) && property_exists($values , $target)) {
    $feed_values[] = $values->$target;
}