1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32

use clap::Parser;

#[derive(Parser, Debug, PartialEq)]
#[clap(about, author, version)]
struct Opt {
    // Default parser for `try_from_str` is FromStr::from_str.
    // `impl FromStr for bool` parses `true` or `false` so this
    // works as expected.
    #[clap(long, parse(try_from_str))]
    foo: bool,

    // Of course, this could be done with an explicit parser function.
    #[clap(long, parse(try_from_str = true_or_false), default_value_t)]
    bar: bool,

    // `bool` can be positional only with explicit `parse(...)` annotation
    #[clap(parse(try_from_str))]
    boom: bool,
}

fn true_or_false(s: &str) -> Result<bool, &'static str> {
    match s {
        "true" => Ok(true),
        "false" => Ok(false),
        _ => Err("expected `true` or `false`"),
    }
}

fn main() {
    let opt = Opt::parse();
    dbg!(opt);
}