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### The line position iterator

The `line_pos_iterator` is a lightweight line position iterator. This iterator adapter only stores the current line number, nothing else. Unlike Spirit.Classic's `position_iterator`, it does not store the column number and does not need an end iterator. The current column can be computed, if needed.

##### Class Reference

    template <class Iterator>
    class line_pos_iterator : public boost::iterator_adaptor<
        line_pos_iterator<Iterator>  // Derived
      , Iterator                     // Base
      , boost::use_default           // Value
      , boost::forward_traversal_tag // CategoryOrTraversal
    > {
    public:
        line_pos_iterator();

        explicit line_pos_iterator(Iterator);

        std::size_t position() const;

    private:
        friend class boost::iterator_core_access;

        void increment();

        std::size_t line; // The line position.
        typename std::iterator_traits<Iterator>::value_type prev;
    };

##### get_line

    template <class Iterator>
    inline std::size_t get_line(Iterator);

Get the line position. Returns -1 if Iterator is not a `line_pos_iterator`.

##### get_line_start

    template <class Iterator>
    inline Iterator get_line_start(Iterator lower_bound, Iterator current);

Get an iterator to the beginning of the line. Applicable to any iterator.

##### get_current_line

    template <class Iterator>
    inline iterator_range<Iterator>
    get_current_line(Iterator lower_bound, Iterator current,
                     Iterator upper_bound);

Get an `iterator_range` containing the current line. Applicable to any iterator.

##### get_column

    template <class Iterator>
    inline std::size_t get_column(Iterator lower_bound, Iterator current,
                                  std::size_t tabs = 4);

Get the current column. Applicable to any iterator.