DDSXTY13 — Restrictions on MAP key element type should include ENUM

DDS-XTypes 1.2 section 7.2.2.4.3 (Collection Types) on page 30 bottom states:

> * Element type: The concrete type to which all elements conform. (Collection Elements
> that are of a subtype of the element type rather than the element type itself may be
> truncated when they are serialized into a Data Representation.)
> In the case of a map type, this attribute corresponds to the type of the value elements.
> Map types have an additional attribute, the key element type, that indicates the type of the
> may key objects.

I believe there is a typo in "type of the may key objects" - drop the word "may" ?

The paragraph continues:

> Implementers of this specification need only support key elements of
> signed and unsigned integer types and of narrow and wide string types; the behavior of
> maps with other key element types is undefined and may not be portable.

Is there a particular reason why enums were excluded from the supported key types?

Corrections were already applied in the formal document

The typo mentioned in the description was already corrected in the formal DDS-XTYPES 1.2 document.

Allowing enum to be used as key discriminator would introduce problems with type interoperability or data reception. Given that a similar behavior can be achieve at the application level (using the ordinal value associated with each enumeration literal) it seems better to leave the specification with the existing limitation.