Optional or default command arguments

[keck-in-space]

Hello,

I wasn't able to find any information about this, but I'm curious if it is possible to have optional or default command arguments designated in the FPP.

I'd like to be able to do something like this:

        async command BackupData(
            downlink:      bool             @< should the data be downlinked?
            priority:      U8?              @< if downlinking, what priority?
        )

Where the ? designates an optional parameter -- where GDS won't prevent the command from being sent if that argument is empty.

I'd also be fine with some way to designate a default value, something like this, maybe. This would be a functionality where GDS auto fills the defaulted value.

        async command BackupData(
            downlink:      bool             @< should the data be downlinked?
            priority:      U8=15            @< if downlinking, what priority?
        )

Obviously I'm just making up syntax, but does anything like this exist for F Prime?

[thomas-bc]

Arrays, structs and enums can have default values (see user guide), and the GDS does auto-populates them (we recently fixed a bug w.r.t. that though, so make sure you're using GDS v4.1.1a1 or higher). I think that's the closest we have to what you're describing. But that's not available for basic types AFAIK.

Optionally serializing something sounds like trouble (although I'm sure it's possible). You could have the GDS form be optional and still serialize a default, but that's somewhat similar to just using a default value.

[thomas-bc]

All that to say, you can have that behavior by doing something like such:

struct BackupDataArgs { downlink: bool, priority: U8 } default { priority = 15 }

async command BackupData(args: BackupDataArgs)

[keck-in-space]

Excellent! Thank you. This is what I needed to know. Agreed about optional serialization being a problem. This makes sense.