use std::io;
use std::io::prelude::*;
use std::io::{Cursor, SeekFrom};

trait Tell {
    fn tell(&mut self) -> io::Result<u64>;
}

impl<T: Seek> Tell for T {
    fn tell(&mut self) -> io::Result<u64> {
        self.seek(SeekFrom::Current(0))
    }
}

fn main() -> io::Result<()> {
    let mut f = Cursor::new(vec![0; 15]);

    // move the cursor 5 bytes from the start of the file
    f.seek(SeekFrom::Start(5))?;

    println!("{:?}", f.tell());

    Ok(())
}