// Variables for arguments to fill
let mut file = PathBuf::new();
let mut out: Option<PathBuf> = None;
let mut number = 0;

// Set up arguments table
enum Arg { Help, Number, File, Out }
const OPTIONS: Opts<Arg> = Opts::new(&[
  Opt::help_flag(Arg::Help, &["-h", "--help"]).help_text("Show this help and exit."),
  Opt::value(Arg::Number, &["-n", "--number"], "value")
    .help_text("Optionally specify a number (default: 0)"),
  Opt::positional(Arg::File, "file").required()
    .help_text("Input file."),
  Opt::positional(Arg::Out, "out")
    .help_text("Output destination (optional).")
]).with_description("My simple utility.");

// Parse command-line arguments from `std::env::args()`
match OPTIONS.parse_easy(|program_name, id, _opt, _name, arg| {
  match id {
    Arg::Help => {
      OPTIONS.print_full_help(program_name);
      return Ok(ParseControl::Quit);
    }
    Arg::Number => { number = str::parse(arg)?; }
    Arg::File   => { file = arg.into(); }
    Arg::Out    => { out = Some(arg.into()); }
  }
  Ok(ParseControl::Continue)
}) {
  ParseResult::ContinueSuccess => (),
  ParseResult::ExitSuccess     => std::process::exit(0),
  ParseResult::ExitError       => std::process::exit(1),
}

// Print the result variables
println!("{file:?} -> {out:?} (number: {number:?})",
  out = out.unwrap_or(file.with_extension("out")));

Changelog

v0.2.2:

Fixed coerced ArgumentError not being rewritten for positional arguments.
Moved top level includes to pub use.
Hopefully work around licence & read me texts not being included in crate.

v0.2.1:

Fixed licence field in Cargo.toml.

v0.2.0:

Change licence from MIT to MIT OR Apache-2.0.
Moved Opts::parse_map into newly introduced alloc crate, making it accessible for no_std users.
More generic & flexible help API: removed forced newline, moved error writer to StandardErrorUsageWriter, generalised "Usage" line in standard full writer, enough public constructs to roll a custom help writer.
Added the ability to exclude options from short usage, full help, or both.
More tests for validating internal behaviour & enabled CI on GitHub.
Added new no_std examples.

v0.1.1:

Fixed incorrect error message format for coerced parsing errors.
Cleaned up docstring formatting.
Added basic example.

v0.1.0:

Initial release.

Roadmap

Near future:

More control over parsing behaviour (getopt style, no special casing shorts for Windows style flags, etc.)
More practical examples.

Long term:

Strategy for handling exclusive argument groups.
Make use of const traits when they land to improve table setup.

Projects using jaarg (very cool)

Licensing

jaarg is dual-licensed under either the MIT or Apache 2.0 licences. Pick whichever works best for your project.