Get which arg of mutually exclusive ArgGroup was passed

[Qyriad]

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Describe your use case

One of the use cases the documentation lists for ArgGroup is to have a set of mutually exclusive arguments (with .multiple(false)), but the only way to get which of those arguments was passed is to call matches.is_present(name) for every argument in that group. It would be really nice if I could just get which argument of a mutually exclusive argument group was passed. Currently, to do this you have to check each argument individually, doing something like:

let directions = &["left", "right", "forward"];

let matches = App::new("ArgGroup test")
    .arg(Arg::with_name("left")
        .short("-l")
        .long("--left"))
    .arg(Arg::with_name("right")
        .short("-r")
        .long("--right"))
    .arg(Arg::with_name("forward")
        .short("-f")
        .long("--forward"))
    .group(ArgGroup::with_name("direction")
        .required(true)
        .multiple(false)
        .args(directions))
    .get_matches();

let mut passed_direction = None;
for direction in directions {
    if matches.is_present(direction) {
        passed_direction = Some(direction);
    }
}
let passed_direction = passed_direction.unwrap();

Which is kind of tedious, and not very clean.

Describe the solution you'd like

Being able to write something like:

let matches = App::new("ArgGroup test")
    .arg(Arg::with_name("left")
        .short("-l")
        .long("--left"))
    .arg(Arg::with_name("right")
        .short("-r")
        .long("--right"))
    .arg(Arg::with_name("forward")
        .short("-f")
        .long("--forward"))
    .group(ArgGroup::with_name("direction")
        .required(true)
        .multiple(false)
        .args(&["left", "right", "forward"]))
    .get_matches();

let passed_direction = matches.value_of("direction");

would be really nice. value_of() is just an example, there — I'm not particular about the exact API is to get this 🙂

[ldm0]

I think conflicts_with_all might matches your use case.

[pksunkara]

But that's not the thing he is asking for.

[Qyriad]

she*, but I believe you're correct. ArgGroup::multiple() already sets the mutual exclusivity. I'm looking for a way to get which argument in an ArgGroup was passed, from an ArgMatches. I don't see how conflicts_with_all() helps me there.

[ldm0]

Sorry for disturbing, haven't slept much yesterday and my mind isn't clear.

So we need to design a new api specifically for fetching the triggered argument and also the value? @pksunkara .

[pksunkara]

Yes, but this is not a priority for 3.0

[Qyriad]

So we need to design a new api specifically for fetching the triggered argument and also the value?

Ideally, though I would also be fine with an API just for fetching the triggered argument — which would mean that getting the value of that argument would be a separate step.

[DocKDE]

I'd like this as well but I'll be patient :)

[epage]

Currently, when we parse an argument and store its value in ArgMatches, we also store that value under the ArgGroup's name,, as was previously mentioned.

With #3732, we've changed some things related to storing the value which is having me re-think it. In #3405, we are looking at defining actions to allow users to describe how a value should be written to the ArgMatches. #3748 is considering doing the same for arg groups which could include writing out which argument in an arg group was active. This doesn't let you access both the name and value but, as was mentioned, the user can look up the value.