iterator.rs

struct Tokenizer<R: BufRead> {
    reader: R,
    current_line: String,
}

impl<R> Iterator for Tokenizer<R> where R: BufRead {
    type Item = &'a str;
    fn next<'a>(&'a mut self) -> Option<&'a str> {
        self.current_line.clear();
        let bytes_read = self.reader.read_line(&mut self.current_line).unwrap();
        match bytes_read {
            0 => None,
            _ => Some(&self.current_line),
        }
    }                                                                                          
}

output

src/main.rs:37:18: 37:20 error: use of undeclared lifetime name `'a` [E0261]
src/main.rs:37     type Item = &'a str;
                                ^~
src/main.rs:37:18: 37:20 help: run `rustc --explain E0261` to see a detailed explanation
error: aborting due to previous error