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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<'a>> { | |
16 | Some(match self { | |
17 | Mode::Fast => PossibleValue::new("fast"), | |
18 | Mode::Slow => PossibleValue::new("slow"), | |
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 | } |