Structopt: Set minimum number of entries to a Vec argument

[liamdawson]

Say I have a structopt argument:

        #[structopt(name = "foos")]
        foos: Vec<String>,

I can't seem to find a way to pass a requirement to clap saying that _at least_ one value is required, and running the app without passing any values is considered a successful run.

How can I make it mandatory to pass at least one value to foos?

[TeXitoi]

you want https://docs.rs/clap/2.31.1/clap/struct.Arg.html#method.required so something like that:

#[derive(StructOpt, Debug)]
struct Opt {
    #[structopt(raw(required = "true"))]
    foos: Vec<String>,
}

You might also be interested by https://docs.rs/clap/2.31.1/clap/struct.Arg.html#method.min_values you can find a complete example at https://github.com/TeXitoi/structopt/blob/master/examples/at_least_two.rs

Does it answer your question?

[liamdawson]

Yes, that works well, thank you. 👍

[clbarnes]

For anyone coming across this in future, I believe the correct way to do it now is

#[derive(StructOpt, Debug)]
struct Opt {
    #[structopt(required = true)]
    foos: Vec<String>,
}

[vallentin]

To add to @clbarnes update, if you're searching for a way to require a "minimum number of entries" as the title suggested, then you can use min_values = ....

#[derive(StructOpt, Debug)]
struct Opt {
    // #[structopt(required = true, min_values = 2)]
    // same as
    #[structopt(min_values = 2)]
    foos: Vec<String>,
}

If min_values is used, then required is implied. However specifying both is perfectly valid.

[WiSaGaN]

To add to @clbarnes update, if you're searching for a way to require a "minimum number of entries" as the title suggested, then you can use min_values = ....

#[derive(StructOpt, Debug)]
struct Opt {
    // #[structopt(required = true, min_values = 2)]
    // same as
    #[structopt(min_values = 2)]
    foos: Vec<String>,
}

If min_values is used, then required is implied. However specifying both is perfectly valid.

I tried to use only min_values, it still runs successfully when the arg is NOT specified. In this case we do need specify required = true explicitly.