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use clap::{arg, builder::PossibleValue, command, value_parser, ValueEnum};
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
enum Mode {
Fast,
Slow,
}
// Can also be derived with feature flag `derive`
impl ValueEnum for Mode {
fn value_variants<'a>() -> &'a [Self] {
&[Mode::Fast, Mode::Slow]
}
fn to_possible_value(&self) -> Option<PossibleValue> {
Some(match self {
Mode::Fast => PossibleValue::new("fast").help("Run swiftly"),
Mode::Slow => PossibleValue::new("slow").help("Crawl slowly but steadily"),
})
}
}
impl std::fmt::Display for Mode {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.to_possible_value()
.expect("no values are skipped")
.get_name()
.fmt(f)
}
}
impl std::str::FromStr for Mode {
type Err = String;
fn from_str(s: &str) -> Result<Self, Self::Err> {
for variant in Self::value_variants() {
if variant.to_possible_value().unwrap().matches(s, false) {
return Ok(*variant);
}
}
Err(format!("invalid variant: {s}"))
}
}
fn main() {
let matches = command!() // requires `cargo` feature
.arg(
arg!(<MODE>)
.help("What mode to run the program in")
.value_parser(value_parser!(Mode)),
)
.get_matches();
// Note, it's safe to call unwrap() because the arg is required
match matches
.get_one::<Mode>("MODE")
.expect("'MODE' is required and parsing will fail if its missing")
{
Mode::Fast => {
println!("Hare");
}
Mode::Slow => {
println!("Tortoise");
}
}
}
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