DateTime converted to ArrayObject instead of string in custom visitor class

[mvachette]

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no
RFC?	no

I use a custom visitor class (declared using Symfony DIC).

In the "getResult" method, DateTime objects are converted to ArrayObject, instead of string (I can see that in standard JsonSerializationVisitor, DateTime objects are well converted, when printing "$this->getRoot()" in getResults()), that leads to empty string in my final output.

Steps required to reproduce the problem

1. Configure a custom visitor class (I'm using JMS serializer with Symfony)
2. launch serialization with data containing some DateTime objects
3. In the "getResult" method, print the content of this->getRoot()

Expected Result

• DateTime are converted to string at this level (this is what I see if I use standard serializer)

Actual Result

• DateTime object are converted to ArrayObject at this level
• Even if I declare the standard JsonSerializationVisitor class as custom class serializer, the problem occurs: it seems to be related to the use of a custom serilizer class, not to the class itself

Code Extracts

Configuration of custom serializer

custom-serializer:
        class: JMS\Serializer\JsonSerializationVisitor
        arguments: ["@jms_serializer.naming_strategy"]
        tags:
          - { name: jms_serializer.serialization_visitor, format: "custom" }

Serialized data

$data = ['date' => new \DateTime()];
$serializer->serialize($data, 'custom');

Output with "custom" format

Trace in JsonSerializationVisitor:

 public function getResult()
    {
        var_dump($this->getRoot()); exit;

Output

array (size=1)
  'date'=> 
      object(ArrayObject)[5097]
      private 'storage' =>
        array (size=0)
          empty
</pre>

Output using regular "custom" format

array (size=1)
  'date' => string '2018-12-05T11:24:48+01:00' (length=25)