json_encode on class with magic properties

Question

I am trying to json_encode an array of objects who all have magic properties using __get and __set. json_encode completely ignores these, resulting in an array of empty objects (all the normal properties are private or protected).

So, imagine this class:

class Foo
{
    public function __get($sProperty)
    {
        if ($sProperty == 'foo')
        {
            return 'bar!';
        }
        return null;
    }
}

$object = new Foo();
echo $object->foo; // echoes "foo"
echo $object->bar; // warning
echo json_encode($object); // "{}"

I've tried implementing IteratorAggregate and Serializable for the class, but json_encode still doesn't see my magic properties. Since I am trying to encode an array of these objects, an AsJSON()-method on the class won't work either.

Update! It seems the question is easy to misunderstand. How can I tell json_encode which "magic properties" exist? IteratorAggregate didn't work.

BTW: The term from the PHP documentation is "dynamic entities". Whether or not the magic properties actually exist is arguing about semantics.

Answer 1

This is the correct behavior
JSON is only able to contain data not methods - it is meant to be language independent so encoding object methods would not make sense.

Answer 2

From your comment:

I am asking about the magic properties, not the methods. – Vegard Larsen 1 min ago

 

There is no such thing as a magic property.

 

All you have right now is a magic method that gets called when you try to access a non-visible property.

Let's say it again

 

$obj->foo does not exist

 

The way a magic method is implemented is not a concern of PHP, and it can't magically know that you are using your magic method to 'magically' make it look like there is $obj->foo.

If a property does not exist, it will not be put into the object when you json_encode it.

Furthermore, even if json_encode knew that __get was active, it wouldn't know what value to use to call it.

Answer 3

How could it know your properties?

$object = new Foo();
echo $object->foo; // how do you know to access foo and not oof?
                   // how do you expect json_encode to know to access foo?

magic methods are syntactic sugar, and mostly fire back when you use them. this is one such case.

echo json_encode($object); // "{}"

of course it's empty, $object has zero public properties, just a magic method and the ensuing syntactic sugar (turned sour)

Answer 4

I'd create a method on the object to return the internal array.

class Foo
{
    private $prop = array();

    public function __get($sProperty)
    {
       return $this->prop[$sProperty];
    }

    public function __set($sProperty, $value)
    {
       $this->prop[$sProperty] = $value;
    }

    public function getJson(){
        return json_encode($this->prop);
    }
}



$f = new Foo();
$f->foo = 'bar';
$json = $f->getJson();

Answer 5

json_encode() doesn't "asks" the object for any interface. It directly fetches the HashTable pointer that represents the properties of an object by calling obj->get_properties(). It then iterates (again directly, no interface such as Traversable, Iterator etc. is used) over this HashTable and processes the elements that are marked as public. see static void json_encode_array() in ext/json/json.c
That makes it impossible to have a property to show up in the result of json_encode() but not to be accessible as $obj->propname.

edit: I haven't tested it much and forget about "high performance" but you might want to start with

interface EncoderData {
  public function getData();
}

function json_encode_ex_as_array(array $v) {
  for($i=0; $i<count($v); $i++) {
    if ( !isset($v[$i]) ) {
      return false;
    }
  }
  return true;
}

define('JSON_ENCODE_EX_SCALAR', 0);
define('JSON_ENCODE_EX_ARRAY', 1);
define('JSON_ENCODE_EX_OBJECT', 2);
define('JSON_ENCODE_EX_EncoderDataObject', 3);

function json_encode_ex($v) {
  if ( is_object($v) ) {
    $type = is_a($v, 'EncoderData') ? JSON_ENCODE_EX_EncoderDataObject : JSON_ENCODE_EX_OBJECT;
  }
  else if ( is_array($v) ) {
    $type = json_encode_ex_as_array($v) ? JSON_ENCODE_EX_ARRAY : JSON_ENCODE_EX_OBJECT;
  }
  else {
    $type = JSON_ENCODE_EX_SCALAR;
  }

  switch($type) {
    case JSON_ENCODE_EX_ARRAY: // array [...]
      foreach($v as $value) {
        $rv[] = json_encode_ex($value);
      }
      $rv = '[' . join(',', $rv) . ']';
      break;
    case JSON_ENCODE_EX_OBJECT: // object { .... }
      $rv = array();
      foreach($v as $key=>$value) {
        $rv[] = json_encode((string)$key) . ':' . json_encode_ex($value);
      }
      $rv = '{' . join(',', $rv) .'}';
      break;
    case JSON_ENCODE_EX_EncoderDataObject:
      $rv = json_encode_ex($v->getData());
      break;
    default:
      $rv = json_encode($v);
  }
  return $rv;
}

class Foo implements EncoderData {
  protected $name;
  protected $child;

  public function __construct($name, $child) {
    $this->name = $name;
    $this->child = $child;

  }
  public function getData() {
    return array('foo'=>'bar!', 'name'=>$this->name, 'child'=>$this->child);
  }
}


$data = array();
for($i=0; $i<10; $i++) {
  $root = null;
  foreach( range('a','d') as $name ) {
    $root = new Foo($name, $root);
  }
  $data[] = 'iteration '.$i;
  $data[] = $root;
  $root = new StdClass;
  $root->i = $i;
  $data[] = $root;
}
$json = json_encode_ex($data);
echo $json, "\n\n\n";
$data = json_decode($json);
var_dump($data);

There is at least one flaw: It doesn't handle recursion, e.g.

$obj = new StdClass;
$obj->x = new StdClass;
$obj->x->y = $obj;
echo json_encode($obj); // warning: recursion detected...
echo json_encode_ex($obj); // this one runs until it hits the memory limit