rust - StructOpt - 如何为 Vec 提供默认值？

Question

我正在寻找一种方法来初始化 structopt Vec默认情况下具有多个项目的字段。我可以为单个项目做到这一点:

use structopt::StructOpt;

#[derive(Debug, StructOpt)]
pub struct Cli {
    #[structopt(default_value = "foo")]
    foo: Vec<String>,
}

fn main() {
    let cli = Cli::from_iter(Vec::<String>::new());
    assert_eq!(cli.foo, vec!["foo"]);
}

但是如何制作 cli.foo平等让我们说 vec!["foo", "bar"]默认情况下？

Answer 1

我已经听从了 L. Riemer 的建议，似乎实现 FromStr 就足够了。只要:

use structopt::StructOpt;

#[derive(Debug, PartialEq)]
struct Foo(Vec<String>);

impl std::str::FromStr for Foo {
    type Err = Box<dyn std::error::Error>;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Ok(Foo(s.split(",").map(|x| x.trim().to_owned()).collect()))
    }
}

#[derive(StructOpt)]
pub struct Cli {
    #[structopt(long, default_value = "foo, bar")]
    foo: Foo,
}

fn main() {
    let cli = Cli::from_iter(Vec::<String>::new());
    assert_eq!(cli.foo, Foo(vec!["foo".into(), "bar".into()]));

    let cli = Cli::from_iter(vec!["", "--foo", "foo"]);
    assert_eq!(cli.foo, Foo(vec!["foo".into()]));

    let cli = Cli::from_iter(vec!["", "--foo", "foo,bar,baz"]);
    assert_eq!(cli.foo, Foo(vec!["foo".into(), "bar".into(), "baz".into()]));
}