PHP object property notation

Question

I suddenly stuck here:

  $source = (object) array(
      'field_phone' => array(
          'und' => array(
              '0' => array(
                  'value' => '000-555-55-55',
              ),
          ),
      ),
  );

  dsm($source);
  $source_field = "field_phone['und'][0]['value']";
  dsm($source->{$source_field});                    //This notation doesn't work
  dsm($source->field_phone['und'][0]['value']);     //This does

• dsm() is Drupal developer function for debug printing variables, objects and arrays.

Why $source object doesn't understand $obj->{$variable} notation? Notice: Undefined property: stdClass::$field_phone['und']['0']['value']

Answer 1

Because your object does not have a property that is named "field_phone['und'][0]['value']". It has a property that is named "field_phone" which is an array which has an index named "und" which is an array which has an index 0 and so on. But the notation $obj->{$var} does not parse and recursively resolve the name, as it shouldn't. It just looks for the property of the given name on the given object, nothing more. It's not like copy and pasting source code in place of $var there.