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    use crate::io;

    pub struct LineColIterator<I> {
        iter: I,

        /// Index of the current line. Characters in the first line of the input
        /// (before the first newline character) are in line 1.
        line: usize,

        /// Index of the current column. The first character in the input and any
        /// characters immediately following a newline character are in column 1.
        /// The column is 0 immediately after a newline character has been read.
        col: usize,

        /// Byte offset of the start of the current line. This is the sum of lengths
        /// of all previous lines. Keeping track of things this way allows efficient
        /// computation of the current line, column, and byte offset while only
        /// updating one of the counters in `next()` in the common case.
        start_of_line: usize,
    }

    impl<I> LineColIterator<I>
    where
        I: Iterator<Item = io::Result<u8>>,
    {
        pub fn new(iter: I) -> LineColIterator<I> {
            LineColIterator {
                iter,
                line: 1,
                col: 0,
                start_of_line: 0,
            }
        }

        pub fn line(&self) -> usize {
            self.line
        }

        pub fn col(&self) -> usize {
            self.col
        }

        pub fn byte_offset(&self) -> usize {
            self.start_of_line + self.col
        }
    }

    impl<I> Iterator for LineColIterator<I>
    where
        I: Iterator<Item = io::Result<u8>>,
    {
        type Item = io::Result<u8>;

        fn next(&mut self) -> Option<io::Result<u8>> {
            match self.iter.next() {
                None => None,
                Some(Ok(b'\n')) => {
                    self.start_of_line += self.col + 1;
                    self.line += 1;
                    self.col = 0;
                    Some(Ok(b'\n'))
                }
                Some(Ok(c)) => {
                    self.col += 1;
                    Some(Ok(c))
                }
                Some(Err(e)) => Some(Err(e)),
            }
        }
    }