Some union values are "empty" in that they have no case selected. Since discriminators are optional, is the JSON representation of such a union equivalent to an empty struct?

// IDL
union U switch (boolean) {
case TRUE:
  long i;
};

When a value of this union has discriminator FALSE, there is no selected case.

As stated in ECMA-404, JSON does not provide native representation for values like "Infinity", "-Infinity", and "NaN":

Numeric values that cannot be represented as sequences of digits (such as Infinity and NaN) are not permitted.

However, these are values that need to be handled by a JSON encoder and decoder. Therefore, we should provide a standard representation for such values so that all implementations of DDS-JSON can follow the same approach.

Define mapping of numeric values that cannot be represented as digit sequences

This resolution provides a mapping for numeric values (such as "Infinity", "-Infinity", and "Nan") that cannot be represented as digit sequences and are therefore invalid JSON according to [ECMA-404].