Verify the value is from an enumerated set of [PossibleValue][crate::builder::PossibleValue].

See also:

• EnumValueParser for directly supporting [ValueEnum][crate::ValueEnum] types
• TypedValueParser::map for adapting values to a more specialized type, like an external enums that can't implement [ValueEnum][crate::ValueEnum]

Example

Usage:

# use clap_builder as clap;
let mut cmd = clap::Command::new("raw")
    .arg(
        clap::Arg::new("color")
            .value_parser(clap::builder::PossibleValuesParser::new(["always", "auto", "never"]))
            .required(true)
    );

let m = cmd.try_get_matches_from_mut(["cmd", "always"]).unwrap();
let port: &String = m.get_one("color")
    .expect("required");
assert_eq!(port, "always");

Semantics:

# use clap_builder as clap;
# use std::ffi::OsStr;
# use clap::builder::TypedValueParser;
# let cmd = clap::Command::new("test");
# let arg = None;
let value_parser = clap::builder::PossibleValuesParser::new(["always", "auto", "never"]);
assert!(value_parser.parse_ref(&cmd, arg, OsStr::new("random")).is_err());
assert!(value_parser.parse_ref(&cmd, arg, OsStr::new("")).is_err());
assert_eq!(value_parser.parse_ref(&cmd, arg, OsStr::new("always")).unwrap(), "always");
assert_eq!(value_parser.parse_ref(&cmd, arg, OsStr::new("auto")).unwrap(), "auto");
assert_eq!(value_parser.parse_ref(&cmd, arg, OsStr::new("never")).unwrap(), "never");