Make API consistent

[chapulina]

Desired behavior

Some things that we should double-check:

• setters should start with Set
• POD arguments don't need to be declared const
• getters should be const
• see more on our style guide

Alternatives considered

Have users memorize what classes have what API styles.

Implementation suggestion

New functions can be added to ign-math6, modifications need to target main. We've been deprecating the old functions on main, for example:

https://github.com/ignitionrobotics/ign-math/blob/931d058e7a9ffb8a123017d255fb876f6724630d/include/ignition/math/Quaternion.hh#L369-L378

But we could consider postponing these deprecation warnings, considering that they will impact lots of users. The goal is to provide users a nice consistent API, and we can accomplish this without adding migration burden.

Here's the status:

1. Angle
2. AxisAlignedBox
3. Box
4. Color
5. Cylinder
6. DiffDriveOdometry
7. Filter
8. Frustum
9. GaussMarkovProcess
10. graph/Edge
11. graph/GraphAlgorithms
12. graph/Graph
13. graph/Vertex
14. Helpers
15. Inertial
16. Kmeans
17. Line2
18. Line3
19. MassMatrix3
20. Material
21. MaterialType
22. Matrix3
23. Matrix4
24. MovingWindowFilter
25. OrientedBox
26. PID
27. Plane
28. Pose3
29. Quaternion. See pull request #327.
30. Rand
31. RollingMean
32. RotationSpline
33. SemanticVersion
34. SignalStats
35. Sphere
36. SphericalCoordiantes
37. Spline
38. Stopwatch
39. Temperature
40. Triangle3
41. Triangle
42. Vector2
43. Vector3
44. Vector3Stats
45. Vector4

Additional context

This was broken off #101.

[akshatpandya]

I'd like to take up this issue. Any update to the above list or I can just start?

[chapulina]

Thanks for the help, @akshatpandya ! I think the list is up-to-date, but it's possible that some classes there don't need any changes. If you notice that a class doesn't need changes, please comment here and we can check if off.

[akshatpandya]

@chapulina Should I branch off from main or ign-math6?

[akshatpandya]

@chapulina The following classes doesn't need changes:

1. AxisAlignedBox
2. Box
3. Color
4. Cylinder

I've made changes for the following classes:

1. Angle
2. DiffDriveOdometry

Working on the remaining ones.

[chapulina]

Should I branch off from main or ign-math6?

You can target ign-math6 if you just need to add functions. If you're changing any function signatures then target main 👍

The following classes doesn't need changes:

Thanks! Updated the ticket.

I've made changes for the following classes:

Did you mean to close the PRs? Let us know if you have any questions. I noticed you added const to the double parameters, but we should be removing const from "plain old data" (POD) like double, see the style guide:

For a function parameter passed by value, const has no effect on the caller, thus is not recommended in function declarations.

[akshatpandya]

@chapulina I've opened a PR for the following updated classes:

Angle
DiffDriveOdometry
Filter
Frustum
GaussMarkovProcess
graph/Edge
graph/GraphAlgorithms
graph/Graph
graph/Vertex