Get which arg of mutually exclusive ArgGroup was passed

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Issue by Qyriad
Thursday Jan 28, 2021 at 20:44 GMT
Originally opened as clap-rs/clap#2317

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• Searched the discussions
• Searched the closed issues

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 🙂

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Comment by ldm0
Friday Jan 29, 2021 at 16:44 GMT

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I think conflicts_with_all might matches your use case.

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Comment by pksunkara
Friday Jan 29, 2021 at 18:05 GMT

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

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Comment by Qyriad
Friday Jan 29, 2021 at 18:39 GMT

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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.

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Comment by ldm0
Saturday Jan 30, 2021 at 04:21 GMT

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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 .

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Comment by pksunkara
Saturday Jan 30, 2021 at 10:30 GMT

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Yes, but this is not a priority for 3.0

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Comment by Qyriad
Saturday Jan 30, 2021 at 15:54 GMT

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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.

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Comment by DocKDE
Tuesday Oct 26, 2021 at 18:15 GMT

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