Keeping track of argument position in lexopt

tracking_iterator.rs

use std::cell::RefCell;
use std::rc::Rc;

struct TrackingIterator<T>(Rc<RefCell<(u64, T)>>);

impl<T> TrackingIterator<T> {
    fn new(inner: T) -> Self {
        Self(Rc::new(RefCell::new((0, inner))))
    }

    fn position(&self) -> u64 {
        self.0.borrow().0
    }
}

impl<T> Clone for TrackingIterator<T> {
    fn clone(&self) -> Self {
        Self(self.0.clone())
    }
}

impl<T> Iterator for TrackingIterator<T>
where
    T: Iterator,
{
    type Item = T::Item;

    fn next(&mut self) -> Option<T::Item> {
        let mut inner = self.0.borrow_mut();
        inner.0 += 1;
        inner.1.next()
    }
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut args = std::env::args_os();
    args.next();
    let args = TrackingIterator::new(args);
    let mut parser = lexopt::Parser::from_args(args.clone());
    while let Some(arg) = parser.next()? {
        println!("{:?} at pos {}", arg, args.position());
    }
    Ok(())
}