1 | use clap::{arg, builder::PossibleValue, command, value_parser, ValueEnum}; |
2 | |
3 | #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)] |
4 | enum Mode { |
5 | Fast, |
6 | Slow, |
7 | } |
8 | |
9 | // Can also be derived with feature flag `derive` |
10 | impl ValueEnum for Mode { |
11 | fn value_variants<'a>() -> &'a [Self] { |
12 | &[Mode::Fast, Mode::Slow] |
13 | } |
14 | |
15 | fn to_possible_value<'a>(&self) -> Option<PossibleValue> { |
16 | Some(match self { |
17 | Mode::Fast => PossibleValue::new("fast" ).help("Run swiftly" ), |
18 | Mode::Slow => PossibleValue::new("slow" ).help("Crawl slowly but steadily" ), |
19 | }) |
20 | } |
21 | } |
22 | |
23 | impl std::fmt::Display for Mode { |
24 | fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { |
25 | self.to_possible_value() |
26 | .expect("no values are skipped" ) |
27 | .get_name() |
28 | .fmt(f) |
29 | } |
30 | } |
31 | |
32 | impl std::str::FromStr for Mode { |
33 | type Err = String; |
34 | |
35 | fn from_str(s: &str) -> Result<Self, Self::Err> { |
36 | for variant in Self::value_variants() { |
37 | if variant.to_possible_value().unwrap().matches(s, false) { |
38 | return Ok(*variant); |
39 | } |
40 | } |
41 | Err(format!("invalid variant: {s}" )) |
42 | } |
43 | } |
44 | |
45 | fn main() { |
46 | let matches = command!() // requires `cargo` feature |
47 | .arg( |
48 | arg!(<MODE>) |
49 | .help("What mode to run the program in" ) |
50 | .value_parser(value_parser!(Mode)), |
51 | ) |
52 | .get_matches(); |
53 | |
54 | // Note, it's safe to call unwrap() because the arg is required |
55 | match matches |
56 | .get_one::<Mode>("MODE" ) |
57 | .expect("'MODE' is required and parsing will fail if its missing" ) |
58 | { |
59 | Mode::Fast => { |
60 | println!("Hare" ); |
61 | } |
62 | Mode::Slow => { |
63 | println!("Tortoise" ); |
64 | } |
65 | } |
66 | } |
67 | |