C++ command-based examples use both Command* and CommandPtr for GetAutonomousCommand

[rzblue]

The examples show GetAutonomousCommand returning both CommandPtr and Command* in various places.

In some examples, GetAutonomousCommand constructs and returns a Command* constructed with the new operator, leaking memory.
In others, it returns pointers to commands constructed inside RobotContainer (which obviously can't be accomplished with CommandPtr due to ownership constraints- functions that return CommandPtr must construct a new command each time)
)

Additionally, SendableChooser must be used with Command*.

It seems like there's not one way that will work for all cases.

I'm not sure what the best solution is here. Perhaps we should keep the examples as-is, and better document the differences between CommandPtr and Command*?

[Starlight220]

In some examples, GetAutonomousCommand constructs and returns a Command* constructed with the new operator, leaking memory.

This is a leftover from before CommandPtr was a thing (and possibly even from old commands).

it returns pointers to commands constructed inside RobotContainer (which obviously can't be accomplished with CommandPtr due to ownership constraints- functions that return CommandPtr must construct a new command each time)

CommandPtr or Command*? Returning Command* from a CommandPtr owned elsewhere with the correct lifetime (such as RobotContainer) is ok. As long as ppl don't start composing it.

Additionally, SendableChooser must be used with Command*.

That's been brought up before; there are multiple options:

• Choose between Command*, own the commands externally in RobotContainer
• Choose between function<CommandPtr()>.
• Choose between strings/ints/enums/etc, feed them into SelectCommand. (Maybe add a class for doing this?)

better document the differences between CommandPtr and Command*?

I think we have some docs in the C++ Commands page, but improving it and/or putting it somewhere more obvious is never a bad idea.
Having concepts might improve this, might make it more confusing due to a bunch of type names.

[Starlight220]

To clarify, the action items I see from this issue are:

• Eliminate the memory leaks from newing auto commands (this can be done by owning the command in RobotContainer, or constructing and passing a CommandPtr). (resolved by [wpilibcExamples] Update examples to CommandPtr #5988)
• Document differences between CommandPtr (owned) and Command* (non-owned). --> extracted to Document differences between CommandPtr (owned) and Command* (non-owned) frc-docs#2438
• Better showcase usage of how to use CommandPtr in conjunction with SendableChooser (preferably, have examples for all three ways). (mostly resolved by [wpilibcExamples] Update examples to CommandPtr #5988, maybe enhance examples for all three methods)

Using concepts for command types should also be done, but I see that as deriving more from #5789 than from this issue.

[ncorrea210]

• Document differences between CommandPtr (owned) and Command* (non-owned).

Is there any plan as to where this may be documented? Is it going to be one long comment on every single GetAutonomousCommand() or will there be a link to a new page(or an addition to an old one) on the FRC Docs? Or something else entirely, though I am not sure of many other options.

[Starlight220]

The C++ Commands Technical Discussion page on frc-docs, though it might need a refactor/split/rework (it currently has a lot of historic information that is relevant to command classes and less so to CommandPtr).

[Starlight220]

I extracted the remaining documentation part to wpilibsuite/frc-docs#2438; closing.