fncli

An attribute macro to simplify writing simple command line applications.

Example

```rust

[fncli::cli]

fn main(a: i32, b: i32) { println!("{}", a + b); } ```

rust $ cargo run 1 2 3

``rust $ cargo run 1 missing argument:b: i32`

USAGE: target/debug/examples/add ```

```rust $ cargo run 1 2 3 too many arguments (expected 2)

USAGE: target/debug/examples/add ```

``rust $ cargo run 1 a failed to parse argument:b: i32` (ParseIntError { kind: InvalidDigit })

USAGE: target/debug/examples/add ```

For a more complete example, see the time elapsed example.

How It Works

```rust fn main() { let (a, b) = { let mut args = std::env::args();

    let cmd = args.next().expect("should have a command name");

    let exit = |err: &str| -> ! {
        eprintln!("{err}");
        eprintln!();
        eprintln!("USAGE:\n    {cmd} <a: i32> <b: i32>");
        std::process::exit(1)
    };

    let tuple = (
        i32::from_str(
            &args
                .next()
                .unwrap_or_else(|| exit("missing argument: `a: i32`")),
        )
        .unwrap_or_else(|e| exit(&format!("failed to parse argument `a: i32` ({e:?})"))),
        i32::from_str(
            &args
                .next()
                .unwrap_or_else(|| exit("missing argument: `b: i32`")),
        )
        .unwrap_or_else(|e| exit(&format!("failed to parse argument `b: i32` ({e:?})"))),
    );

    if args.next().is_some() {
        exit("too many arguments (expected 2)");
    }

    tuple
};

{
    println!("{}", a + b);
}

} ```

The generated code is very simple, and not too different from how one would write the code by hand.