allow modern enum class/scoped enums with type specifier and assigning values

[JSG-0]

Scoped enums have been available since C++-11 (13 years ago). Other DDS implementations support this in their IDL.
The advantages are well documented.

Add IDL support for scoped enums a.k.a. "enum classes" with a type specified "enum base" that can be any cstdint and allow specifying a value for each enumeration independently, including negative values, and since scoped allow different enums to reuse label names.

[JLBuenoLopez]

@JSG-0

Thanks for your contribution. According to Fast DDS CONTRIBUTING guidelines I am moving this ticket to the Ideas forum where feature requests are discussed.

On the one hand, enum class support has been introduced in #271 into the development branch feature/xtypes_typeobject. This branch will be merged and released soon.

On the other hand, I am afraid that support for @bit_bound builtin annotation that allows modifying the enum base and the @value builtin annotation that allows setting the value of each enumeration literal, is not in the current roadmap. You might contact eProsima's commercial support team to discuss options to accelerate their development.

Regarding the scope, this is something already supported in the current Fast DDS-Gen. Nevertheless I have issued eProsima/dds-types-test#22 to add this specific test case into Fast DDS-Gen CI. The CI is updated in #292.

[JSG-0]

Thanks for the quick response: dealing with large volume of real-time messages with lots of enums, and never need more than 8 bits. Being forced into uint32 is a big waste. And there are interface requirements specifying negative enum values and with very specific non-monitorically increasing values.

[JSG-0]

Is it on the roadmap yet to allow me to specify custom, random values for enums yet? Including negative values?

[richiware]

Added support in #379