AP_ExternalAHRS: Change the define definition to an enum class

[muramura]

The define definition is grouped with a group name.
I will change it to ENUM CLASS.

[amilcarlucas]

Binary Name      Text [B]     Data [B]     BSS (B)      Total Flash Change [B] (%)      Flash Free After PR (B)
---------------  -----------  -----------  -----------  ----------------------------  -------------------------
arducopter       0 (0.0000%)  0 (0.0000%)  0 (0.0000%)  0 (0.0000%)                                      154952
antennatracker   0 (0.0000%)  0 (0.0000%)  0 (0.0000%)  0 (0.0000%)                                      625228
arducopter-heli  0 (0.0000%)  0 (0.0000%)  0 (0.0000%)  0 (0.0000%)                                      155960
ardusub          0 (0.0000%)  0 (0.0000%)  0 (0.0000%)  0 (0.0000%)                                      364492
ardurover        0 (0.0000%)  0 (0.0000%)  0 (0.0000%)  0 (0.0000%)                                      306200
blimp            0 (0.0000%)  0 (0.0000%)  0 (0.0000%)  0 (0.0000%)                                      603104
arduplane        0 (0.0000%)  0 (0.0000%)  0 (0.0000%)  0 (0.0000%)                                      157896

@muramura Can you check if the binary output is equal as well?

[muramura]

@amilcarlucas san.

AFTER and BEFORE are the same size.

AFTER

BUILD SUMMARY
Build directory: /home/parallels/work2/ardupilot/build/fmuv3
Target Text (B) Data (B) BSS (B) Total Flash Used (B) Free Flash (B) External Flash Used (B)

bin/arducopter 1557289 3892 192868 1561181 519572 Not Applicable

BEFORE

BUILD SUMMARY
Build directory: /home/parallels/work2/ardupilot/build/fmuv3
Target Text (B) Data (B) BSS (B) Total Flash Used (B) Free Flash (B) External Flash Used (B)

bin/arducopter 1557289 3892 192868 1561181 519572 Not Applicable

[peterbarker]

I'm not in favour of this as it currently stands.

The static casts make it far less readable.

It could be done with something like a has_status method, but I don't think we need to go there.

I'm going to ping @valentinb on this PR - he's most recently changed this stuff and can either back me up or say he loves it and would love to have it pushed forward.

[peterbarker]

Suggested change

	enum class ILABS_UNIT_STATUS : uint16_t {
	enum class UnitStatus : uint16_t {

similarly elsewhere

[muramura]

I changed the ENUM name.

[peterbarker]

You can't tell me this looks better!

There are ways this could be done to look quite nice, but this is not one of them!

[muramura]

I believe that by using ENUM CLASS, we can detect the bug in #28111 at the coding stage.

[muramura]

#28111 fix has been included.

[valbv]

Hello. A couple of days ago I updated the part with InertialLabs EAHRS handler
No need to mention "valentinb", he is another Valentine:)

Thanks for finding and fixing the bug

I can't say anything about using "define" or "enum class".
The abundance of "static_cast" really adds a lot of text.

[Ryanf55]

An alternative approach to a static cast is to add an overload to the unary + operator on the enum class.
This is recommended by some developers on the C++ standard here:
https://groups.google.com/a/isocpp.org/g/std-proposals/c/eiN1Xqrt59Y/m/DscuM2ViDAAJ

Advantages:

• Shorter syntax than static cast
• Only allowed on enums you add the operator for
• Preserves type safety of enum class

Disadvantages:

• + as an operator isn't obvious to all devs what it does because it's a less common operator
• You need to add this operator overload to every enum you want to cast in this way