// Note: this requires the `derive` feature

use clap::Parser;
use std::error::Error;

#[derive(Parser, Debug)]
struct Args {
    #[clap(short = 'D', parse(try_from_str = parse_key_val), multiple_occurrences(true))]
    defines: Vec<(String, i32)>,
}

/// Parse a single key-value pair
fn parse_key_val<T, U>(s: &str) -> Result<(T, U), Box<dyn Error + Send + Sync + 'static>>
where
    T: std::str::FromStr,
    T::Err: Error + Send + Sync + 'static,
    U: std::str::FromStr,
    U::Err: Error + Send + Sync + 'static,
{
    let pos = s
        .find('=')
        .ok_or_else(|| format!("invalid KEY=value: no `=` found in `{}`", s))?;
    Ok((s[..pos].parse()?, s[pos + 1..].parse()?))
}

fn main() {
    let args = Args::parse();
    println!("{:?}", args);
}