eclipse-aascw / aas-core-codegen / 35260547425

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Compose the Python JSON serialization (#709)

Every concrete class carried a ``transform_<cls>`` method on the
``_Serializer``, and every nested value in it went through
``self.transform``, which is three Python frames: the ``transform`` of
the transformer, the ``transform`` of the instance, and the method which
finally writes the properties. The framing of a list was spelled out at
each list-typed properties. A class now costs one module-level function
plus an entry in the transformer:

    def _submodel_element_collection_to_jsonable(
        that: aas_types.SubmodelElementCollection
    ) -> MutableMapping[str, MutableJsonable]:
        """Serialize :paramref:`that` to a JSON-able representation."""
        jsonable: MutableMapping[str, MutableJsonable] = dict()
        if that.extensions is not None:
            jsonable['extensions'] = _list_of__extension_to_jsonable(
                that.extensions
            )
        if that.category is not None:
            jsonable['category'] = that.category
        ...
        if that.value is not None:
            jsonable['value'] = _list_of__submodel_element_to_jsonable(
                that.value
            )
        jsonable['modelType'] = 'SubmodelElementCollection'
        return jsonable

The rationale and the design, dual to the de-serialization:

* One shape for every serializer, ``value 🠒 JSON-able value``. As on the
  reading side, and unlike the XML side, the serializers need no
  combinator tower: a JSON value is not framed by anything which
  encloses it, so the value at a key already is the whole value, and
  only a list and a tuple have to be composed at all.

* The composed serializers are de-duplicated by the type which they
  serialize and are named out of the same monikers as the parsers,
  so that ``_list_of__reference_to_jsonable`` stands beside
  ``_list_of__reference_from_jsonable``. They are module-level
  functions, so nothing whatsoever is composed at the time of the
  seriali... (continued)

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