diff --git a/src/core/BufferLineWalker.cc b/src/core/BufferLineWalker.cc
index 77e6305..c6d7e55 100644
--- a/src/core/BufferLineWalker.cc
+++ b/src/core/BufferLineWalker.cc
@@ -2,100 +2,100 @@
 
 /**
  * Construct a BufferLineWalker.
+ *
+ * @param buffer The Buffer we're iterating.
+ * @param start_of_line Buffer iterator pointing to the beginning of the buffer line.
+ * @param view_width View width, beyond which characters will wrap to the next line.
+ * @param character_width_determiner Functor to return the width (in columns) of a character.
  */
 BufferLineWalker::BufferLineWalker(
         std::shared_ptr<Buffer> buffer,
+        std::shared_ptr<Buffer::Iterator> start_of_line,
+        int view_width,
         CharacterWidthDeterminer & character_width_determiner)
     : m_buffer(buffer),
       m_character_width_determiner(character_width_determiner)
 {
-    m_width = 1;
+    m_view_width = view_width;
+    m_row_offset = 0;
+    m_screen_column = 0;
+    m_virtual_column = 0;
+    m_iterator = std::make_shared<Buffer::Iterator>(*start_of_line);
+    process_new_character();
 }
 
-/**
- * Set the view width.
- *
- * @param width View width.
- */
-void BufferLineWalker::set_width(int width)
+void BufferLineWalker::process_new_character()
 {
-    m_width = std::max(1, width);
-}
-
-/**
- * Invoke the callback for each character in the buffer line, wrapping to the
- * next screen line and taking into account multi-column characters.
- *
- * Callback parameters:
- * - row_offset
- * - screen column
- * - virtual column
- * - character width
- * - buffer iterator
- * If the callback function returns true, iteration continues. Otherwise
- * iteration is terminated.
- *
- * @param start_of_line Buffer iterator pointing to the beginning of the buffer line.
- * @param callback Function to call for each character in the line.
- */
-void BufferLineWalker::walk_line(
-        const Buffer::Iterator & start_of_line,
-        std::function<bool(int, int, int, int, const Buffer::Iterator &)> callback)
-{
-    int row_offset = 0;
-    int screen_column = 0;
-    int virtual_column = 0;
-    Buffer::Iterator i = start_of_line;
-    for (;;)
+    if ((!m_iterator) || (!m_iterator->valid()))
     {
-        uint32_t code_point = *i;
-        if ((code_point == '\n') || (!i.valid()))
-        {
-            callback(row_offset, screen_column, virtual_column, 0, i);
-            break;
-        }
-        int c_width;
-        if (code_point == '\t')
-        {
-            uint8_t tabstop = m_buffer->tabstop();
-            c_width = tabstop - virtual_column % tabstop;
-        }
-        else
-        {
-            c_width = m_character_width_determiner(code_point);
-            if (((screen_column + c_width) > m_width) &&
-                    (screen_column > 0))
-            {
-                row_offset++;
-                screen_column = 0;
-            }
-        }
-        if (!callback(row_offset, screen_column, virtual_column, c_width, i))
-        {
-            break;
-        }
-        virtual_column += c_width;
-        if (code_point == '\t')
-        {
-            screen_column += c_width;
-            while (screen_column >= m_width)
-            {
-                screen_column -= m_width;
-                row_offset++;
-            }
-        }
-        else
-        {
-            if ((screen_column + c_width) >= m_width)
-            {
-                row_offset++;
-                screen_column = 0;
-            }
-            else
-            {
-                screen_column += c_width;
-            }
-        }
-        i.go_forward();
+        m_code_point = '\n';
+        m_character_width = 0;
+        return;
+    }
+
+    m_code_point = **m_iterator;
+
+    if (m_code_point == '\n')
+    {
+        m_character_width = 0;
+        return;
+    }
+
+    if (m_code_point == '\t')
+    {
+        uint8_t tabstop = m_buffer->tabstop();
+        m_character_width = tabstop - m_virtual_column % tabstop;
+        return;
+    }
+
+    m_character_width = m_character_width_determiner(m_code_point);
+
+    if (((m_screen_column + m_character_width) > m_view_width) &&
+            (m_screen_column > 0))
+    {
+        m_row_offset++;
+        m_screen_column = 0;
     }
 }
+
+void BufferLineWalker::operator++(int unused)
+{
+    if (!m_iterator)
+        return;
+
+    if ((m_code_point == '\n') || (!m_iterator->valid()))
+    {
+        m_code_point = '\n';
+        m_iterator.reset();
+        return;
+    }
+
+    /* Adjust virtual column. */
+    m_virtual_column += m_character_width;
+
+    /* Adjust screen position. */
+    if (m_code_point == '\t')
+    {
+        m_screen_column += m_character_width;
+        while (m_screen_column >= m_view_width)
+        {
+            m_screen_column -= m_view_width;
+            m_row_offset++;
+        }
+    }
+    else
+    {
+        if ((m_screen_column + m_character_width) >= m_view_width)
+        {
+            m_row_offset++;
+            m_screen_column = 0;
+        }
+        else
+        {
+            m_screen_column += m_character_width;
+        }
+    }
+
+    m_iterator->go_forward();
+    process_new_character();
+}
diff --git a/src/core/BufferLineWalker.h b/src/core/BufferLineWalker.h
index 56f51b8..3e4fb28 100644
--- a/src/core/BufferLineWalker.h
+++ b/src/core/BufferLineWalker.h
@@ -14,16 +14,42 @@ class BufferLineWalker
 public:
     BufferLineWalker(
             std::shared_ptr<Buffer> buffer,
+            std::shared_ptr<Buffer::Iterator> start_of_line,
+            int view_width,
             CharacterWidthDeterminer & character_width_determiner);
-    void set_width(int width);
-    void walk_line(
-            const Buffer::Iterator & start_of_line,
-            std::function<bool(int, int, int, int, const Buffer::Iterator &)> callback);
+    void operator++() { return (*this)++; }
+    void operator++(int unused);
+    bool is_eol() const
+    {
+        if (is_valid())
+        {
+            return (m_code_point == '\n');
+        }
+        return false;
+    }
+    bool is_valid() const
+    {
+        return (bool)m_iterator;
+    }
+    int row_offset() const { return m_row_offset; }
+    int screen_column() const { return m_screen_column; }
+    int virtual_column() const { return m_virtual_column; }
+    int character_width() const { return m_character_width; }
+    uint32_t code_point() const { return m_code_point; }
+    std::shared_ptr<Buffer::Iterator> iterator() const { return m_iterator; }
 
 protected:
     std::shared_ptr<Buffer> m_buffer;
+    std::shared_ptr<Buffer::Iterator> m_iterator;
     CharacterWidthDeterminer & m_character_width_determiner;
-    int m_width;
+    int m_view_width;
+    int m_row_offset;
+    int m_screen_column;
+    int m_virtual_column;
+    int m_character_width;
+    uint32_t m_code_point;
+
+    void process_new_character();
 };
 
 #endif
diff --git a/src/core/BufferView.cc b/src/core/BufferView.cc
index 8464d01..eae9a8f 100644
--- a/src/core/BufferView.cc
+++ b/src/core/BufferView.cc
@@ -5,20 +5,22 @@
 BufferView::BufferView(std::shared_ptr<Buffer> buffer,
         std::shared_ptr<Buffer::Iterator> iterator,
         CharacterWidthDeterminer & character_width_determiner)
-    : m_iterator(iterator)
+    : m_buffer(buffer),
+      m_iterator(iterator),
+      m_character_width_determiner(character_width_determiner)
 {
+    m_width = 1;
     m_height = 1;
     m_scroll_offset = 0;
     m_cursor_screen_row = 0;
     m_cursor_screen_column = 0;
     m_cursor_virtual_column = 0;
     m_cursor_row_offset = 0;
-    m_buffer_line_walker = std::make_shared<BufferLineWalker>(buffer, character_width_determiner);
 }
 
 void BufferView::resize(int width, int height)
 {
-    m_buffer_line_walker->set_width(width);
+    m_width = std::max(1, width);
     m_height = std::max(1, height);
 }
 
@@ -27,21 +29,12 @@ void BufferView::set_scroll_offset(int scroll_offset)
     m_scroll_offset = std::max(0, scroll_offset);
 }
 
-void BufferView::iter_lines(
-        std::function<bool(int, const Buffer::Iterator &)> callback)
+BufferView::Iterator BufferView::vert_iter()
 {
     if (m_iterator->valid())
     {
+        /* TODO: user calls update() before vert_iter(). */
         update();
-        Buffer::Iterator i = *m_first_line;
-        int row_offset = m_first_line_row_offset;
-        while (row_offset < m_height)
-        {
-            callback(row_offset, i);
-            row_offset += calculate_rows_in_line(i);
-            if (!i.go_next_line())
-                break;
-        }
     }
     else
     {
@@ -49,6 +42,7 @@ void BufferView::iter_lines(
         m_cursor_screen_column = 0;
         m_cursor_virtual_column = 0;
     }
+    return Iterator(*this);
 }
 
 /**************************************************************************
@@ -58,12 +52,12 @@ void BufferView::iter_lines(
 void BufferView::update()
 {
     std::list<std::pair<int, std::shared_ptr<Buffer::Iterator>>> backward_lines;
-    Buffer::Iterator start_of_line = *m_iterator;
-    start_of_line.go_start_of_line();
+    auto start_of_line = std::make_shared<Buffer::Iterator>(*m_iterator);
+    start_of_line->go_start_of_line();
     int rows_in_cursor_line = calculate_rows_in_cursor_line(start_of_line);
     int so = effective_scroll_offset();
-    int rows_above = screen_rows_above_line(*m_iterator, backward_lines) + m_cursor_row_offset;
-    int rows_below = screen_rows_below_line(*m_iterator) + std::max(0, rows_in_cursor_line - m_cursor_row_offset - 1);
+    int rows_above = screen_rows_above_line(start_of_line, backward_lines) + m_cursor_row_offset;
+    int rows_below = screen_rows_below_line(start_of_line) + std::max(0, rows_in_cursor_line - m_cursor_row_offset - 1);
     int min_rows_to_leave_above = std::min(rows_above, so);
     int min_rows_to_leave_below = std::min(rows_below, so);
     m_cursor_screen_row = std::min(m_height - min_rows_to_leave_below - 1, m_cursor_screen_row);
@@ -89,49 +83,51 @@ void BufferView::update()
     }
 }
 
-int BufferView::calculate_rows_in_line(const Buffer::Iterator & start_of_line)
+int BufferView::calculate_rows_in_line(std::shared_ptr<Buffer::Iterator> start_of_line)
 {
     int saved_row_offset = 0;
-    walk_line(start_of_line, [&saved_row_offset](int row_offset, int screen_column, int virtual_column, int character_width, const Buffer::Iterator & i) -> bool {
-        uint32_t code_point = *i;
-        if ((code_point != '\n') &&
-                (code_point != Buffer::Iterator::INVALID_CODE_POINT))
+    for (auto it = horiz_iter(start_of_line); it.is_valid(); it++)
+    {
+        if (!it.is_eol())
         {
-            saved_row_offset = row_offset;
-            return true;
+            saved_row_offset = it.row_offset();
         }
-        return false;
-    });
+        else
+        {
+            break;
+        }
+    }
     return saved_row_offset + 1;
 }
 
-int BufferView::calculate_rows_in_cursor_line(const Buffer::Iterator & start_of_line)
+int BufferView::calculate_rows_in_cursor_line(std::shared_ptr<Buffer::Iterator> start_of_line)
 {
     int saved_row_offset = 0;
-    walk_line(start_of_line, [this, &saved_row_offset](int row_offset, int screen_column, int virtual_column, int character_width, const Buffer::Iterator & i) -> bool {
-        uint32_t code_point = *i;
-        if (i == *m_iterator)
+    for (auto it = horiz_iter(start_of_line); it.is_valid(); it++)
+    {
+        if (*it.iterator() == *m_iterator)
         {
-            m_cursor_virtual_column = virtual_column;
-            m_cursor_screen_column = screen_column;
-            m_cursor_row_offset = row_offset;
+            m_cursor_virtual_column = it.virtual_column();
+            m_cursor_screen_column = it.screen_column();
+            m_cursor_row_offset = it.row_offset();
         }
-        if ((code_point != '\n') &&
-                (code_point != Buffer::Iterator::INVALID_CODE_POINT))
+        if (!it.is_eol())
         {
-            saved_row_offset = row_offset;
-            return true;
+            saved_row_offset = it.row_offset();
         }
-        return false;
-    });
+        else
+        {
+            break;
+        }
+    }
     return saved_row_offset + 1;
 }
 
-int BufferView::screen_rows_below_line(const Buffer::Iterator & line)
+int BufferView::screen_rows_below_line(std::shared_ptr<Buffer::Iterator> line)
 {
-    Buffer::Iterator i = line;
+    auto i = std::make_shared<Buffer::Iterator>(*line);
     int rows = 0;
-    while ((rows < m_height) && i.go_next_line())
+    while ((rows < m_height) && i->go_next_line())
     {
         rows += calculate_rows_in_line(i);
     }
@@ -139,16 +135,16 @@ int BufferView::screen_rows_below_line(const Buffer::Iterator & line)
 }
 
 int BufferView::screen_rows_above_line(
-        const Buffer::Iterator & line,
+        std::shared_ptr<Buffer::Iterator> line,
         std::list<std::pair<int, std::shared_ptr<Buffer::Iterator>>> & backward_lines)
 {
-    Buffer::Iterator i = line;
+    auto i = std::make_shared<Buffer::Iterator>(*line);
     int rows = 0;
-    while ((rows < m_height) && i.go_previous_line())
+    while ((rows < m_height) && i->go_previous_line())
     {
         int rows_in_this_line = calculate_rows_in_line(i);
         rows += rows_in_this_line;
-        backward_lines.push_back(std::pair<int, std::shared_ptr<Buffer::Iterator>>(rows_in_this_line, std::make_shared<Buffer::Iterator>(i)));
+        backward_lines.push_back(std::pair<int, std::shared_ptr<Buffer::Iterator>>(rows_in_this_line, std::make_shared<Buffer::Iterator>(*i)));
     }
     return rows;
 }
diff --git a/src/core/BufferView.h b/src/core/BufferView.h
index 441c99f..3476690 100644
--- a/src/core/BufferView.h
+++ b/src/core/BufferView.h
@@ -13,45 +13,89 @@
 class BufferView
 {
 public:
+    class Iterator
+    {
+    public:
+        Iterator(BufferView & bv) : m_buffer_view(bv)
+        {
+            if (bv.m_iterator->valid())
+            {
+                m_iterator = std::make_shared<Buffer::Iterator>(*m_buffer_view.m_first_line);
+                m_row_offset = m_buffer_view.m_first_line_row_offset;
+            }
+        }
+        void operator++()
+        {
+            (*this)++;
+        }
+        void operator++(int unused)
+        {
+            if (is_valid())
+            {
+                m_row_offset += m_buffer_view.calculate_rows_in_line(m_iterator);
+                if ((m_row_offset >= m_buffer_view.m_height) || (!m_iterator->go_next_line()))
+                {
+                    m_iterator.reset();
+                }
+            }
+        }
+        bool is_valid()
+        {
+            return (bool)m_iterator;
+        }
+        int row_offset() const
+        {
+            return m_row_offset;
+        }
+        std::shared_ptr<Buffer::Iterator> iterator() const
+        {
+            return m_iterator;
+        }
+
+    protected:
+        BufferView & m_buffer_view;
+        std::shared_ptr<Buffer::Iterator> m_iterator;
+        int m_row_offset;
+    };
+
     BufferView(std::shared_ptr<Buffer> buffer,
             std::shared_ptr<Buffer::Iterator> iterator,
             CharacterWidthDeterminer & character_width_determiner);
     void resize(int width, int height);
     void set_scroll_offset(int scroll_offset);
-    void iter_lines(
-            std::function<bool(int, const Buffer::Iterator &)> callback);
-    void walk_line(
-            const Buffer::Iterator & start_of_line,
-            std::function<bool(int, int, int, int, const Buffer::Iterator &)> callback)
+    Iterator vert_iter();
+    BufferLineWalker horiz_iter(std::shared_ptr<Buffer::Iterator> start_of_line)
     {
-        m_buffer_line_walker->walk_line(start_of_line, callback);
+        return BufferLineWalker(m_buffer, start_of_line, m_width, m_character_width_determiner);
     }
     int cursor_screen_row() const { return m_cursor_screen_row; }
     int cursor_screen_column() const { return m_cursor_screen_column; }
     int cursor_virtual_column() const { return m_cursor_virtual_column; }
 
 protected:
+    std::shared_ptr<Buffer> m_buffer;
     std::shared_ptr<Buffer::Iterator> m_iterator;
     std::shared_ptr<Buffer::Iterator> m_first_line;
     int m_first_line_row_offset;
+    int m_width;
     int m_height;
     int m_scroll_offset;
     int m_cursor_screen_row;
     int m_cursor_screen_column;
     int m_cursor_virtual_column;
     int m_cursor_row_offset;
-    std::shared_ptr<BufferLineWalker> m_buffer_line_walker;
+    CharacterWidthDeterminer & m_character_width_determiner;
 
     int effective_scroll_offset()
     {
         return std::min(m_scroll_offset, (m_height - 1) / 2);
     }
     void update();
-    int calculate_rows_in_line(const Buffer::Iterator & start_of_line);
-    int calculate_rows_in_cursor_line(const Buffer::Iterator & start_of_line);
-    int screen_rows_below_line(const Buffer::Iterator & line);
+    int calculate_rows_in_line(std::shared_ptr<Buffer::Iterator> start_of_line);
+    int calculate_rows_in_cursor_line(std::shared_ptr<Buffer::Iterator> start_of_line);
+    int screen_rows_below_line(std::shared_ptr<Buffer::Iterator> line);
     int screen_rows_above_line(
-            const Buffer::Iterator & line,
+            std::shared_ptr<Buffer::Iterator> line,
             std::list<std::pair<int, std::shared_ptr<Buffer::Iterator>>> & backward_lines);
 };
 
diff --git a/test/src/test_BufferLineWalker.cc b/test/src/test_BufferLineWalker.cc
index 6491ede..c14248a 100644
--- a/test/src/test_BufferLineWalker.cc
+++ b/test/src/test_BufferLineWalker.cc
@@ -16,165 +16,143 @@ class MyCharacterWidthDeterminer : public CharacterWidthDeterminer
     }
 } cld;
 
-TEST(BufferLineWalkerTest, calls_callback_once_for_empty_line)
+TEST(BufferLineWalkerTest, iterats_once_for_empty_line)
 {
     static const uint8_t data[] = "\n";
     std::shared_ptr<Buffer> b = std::make_shared<Buffer>(data, 1u);
-    BufferLineWalker blw(b, cld);
-    blw.set_width(20);
     std::shared_ptr<Buffer::Iterator> start_of_line = b->add_iterator();
-    int times_called = 0;
-    blw.walk_line(*start_of_line, [&times_called](int row_offset, int screen_column, int virtual_column, int character_width, const Buffer::Iterator & it) -> bool {
-            times_called++;
-            EXPECT_EQ(0, row_offset);
-            EXPECT_EQ(0, screen_column);
-            EXPECT_EQ(0, virtual_column);
-            EXPECT_EQ(0, character_width);
-            return true;
-    });
-    EXPECT_EQ(1, times_called);
+    BufferLineWalker blw(b, start_of_line, 20, cld);
+    int iter_count = 0;
+    for (; blw.is_valid(); blw++)
+    {
+        EXPECT_EQ(0, blw.row_offset());
+        EXPECT_EQ(0, blw.screen_column());
+        EXPECT_EQ(0, blw.virtual_column());
+        EXPECT_EQ(0, blw.character_width());
+        EXPECT_TRUE(blw.is_eol());
+        iter_count++;
+    }
+    EXPECT_EQ(1, iter_count);
 }
 
 TEST(BufferLineWalkerTest, walks_correctly_with_tabs_and_no_line_wrapping)
 {
     static const char data[] = "\t1\t12\t123\t1234\t!";
     std::shared_ptr<Buffer> b = std::make_shared<Buffer>((const uint8_t *)data, strlen(data));
-    BufferLineWalker blw(b, cld);
-    blw.set_width(100);
     std::shared_ptr<Buffer::Iterator> start_of_line = b->add_iterator();
-    int times_called = 0;
-    blw.walk_line(*start_of_line, [&times_called](int row_offset, int screen_column, int virtual_column, int character_width, const Buffer::Iterator & it) -> bool {
-            EXPECT_EQ(0, row_offset);
-            static int expected_screen_columns[] = {
-                0,   4, 5,   8, 9, 10,   12, 13, 14, 15,   16, 17, 18, 19, 20,   24, 25
-            };
-            static int expected_character_widths[] = {
-                4,   1, 3,   1, 1, 2,    1, 1, 1, 1,       1, 1, 1, 1, 4,        1, 0
-            };
-            EXPECT_LT(times_called, (int)(sizeof(expected_screen_columns)/sizeof(expected_screen_columns[0])));
-            EXPECT_EQ(expected_screen_columns[times_called], screen_column);
-            EXPECT_EQ(expected_screen_columns[times_called], virtual_column);
-            EXPECT_EQ(expected_character_widths[times_called], character_width);
-            times_called++;
-            return true;
-    });
-    EXPECT_EQ((int)strlen(data) + 1, times_called);
+    BufferLineWalker blw(b, start_of_line, 100, cld);
+
+    static int expected_screen_columns[] = {
+        0,   4, 5,   8, 9, 10,   12, 13, 14, 15,   16, 17, 18, 19, 20,   24, 25
+    };
+    static int expected_character_widths[] = {
+        4,   1, 3,   1, 1, 2,    1, 1, 1, 1,       1, 1, 1, 1, 4,        1, 0
+    };
+    int iter_count = 0;
+    for (; blw.is_valid(); blw++)
+    {
+        EXPECT_EQ(0, blw.row_offset());
+        EXPECT_LT(iter_count, (int)(sizeof(expected_screen_columns)/sizeof(expected_screen_columns[0])));
+        EXPECT_EQ(expected_screen_columns[iter_count], blw.screen_column());
+        EXPECT_EQ(expected_screen_columns[iter_count], blw.virtual_column());
+        EXPECT_EQ(expected_character_widths[iter_count], blw.character_width());
+        iter_count++;
+    }
+    EXPECT_EQ((int)strlen(data) + 1, iter_count);
 }
 
 TEST(BufferLineWalkerTest, walks_correctly_with_tabs_and_line_wrapping)
 {
     static const char data[] = "\t1\t12\t123\t1234\t!";
     std::shared_ptr<Buffer> b = std::make_shared<Buffer>((const uint8_t *)data, strlen(data));
-    BufferLineWalker blw(b, cld);
-    blw.set_width(5);
     std::shared_ptr<Buffer::Iterator> start_of_line = b->add_iterator();
-    int times_called = 0;
-    blw.walk_line(*start_of_line, [&times_called](int row_offset, int screen_column, int virtual_column, int character_width, const Buffer::Iterator & it) -> bool {
-            static int expected_screen_columns[] = {
-                0,   4, 0,   3, 4, 0,   2, 3, 4, 0,   1, 2, 3, 4, 0,   4, 0
-            };
-            static int expected_row_offsets[] = {
-                0,   0, 1,   1, 1, 2,   2, 2, 2, 3,   3, 3, 3, 3, 4,   4, 5
-            };
-            static int expected_virtual_columns[] = {
-                0,   4, 5,   8, 9, 10,   12, 13, 14, 15,   16, 17, 18, 19, 20,   24, 25
-            };
-            static int expected_character_widths[] = {
-                4,   1, 3,   1, 1, 2,    1, 1, 1, 1,       1, 1, 1, 1, 4,        1, 0
-            };
-            EXPECT_LT(times_called, (int)(sizeof(expected_screen_columns)/sizeof(expected_screen_columns[0])));
-            EXPECT_EQ(expected_row_offsets[times_called], row_offset);
-            EXPECT_EQ(expected_screen_columns[times_called], screen_column);
-            EXPECT_EQ(expected_virtual_columns[times_called], virtual_column);
-            EXPECT_EQ(expected_character_widths[times_called], character_width);
-            times_called++;
-            return true;
-    });
-    EXPECT_EQ((int)strlen(data) + 1, times_called);
+    BufferLineWalker blw(b, start_of_line, 5, cld);
+
+    static int expected_screen_columns[] = {
+        0,   4, 0,   3, 4, 0,   2, 3, 4, 0,   1, 2, 3, 4, 0,   4, 0
+    };
+    static int expected_row_offsets[] = {
+        0,   0, 1,   1, 1, 2,   2, 2, 2, 3,   3, 3, 3, 3, 4,   4, 5
+    };
+    static int expected_virtual_columns[] = {
+        0,   4, 5,   8, 9, 10,   12, 13, 14, 15,   16, 17, 18, 19, 20,   24, 25
+    };
+    static int expected_character_widths[] = {
+        4,   1, 3,   1, 1, 2,    1, 1, 1, 1,       1, 1, 1, 1, 4,        1, 0
+    };
+    int iter_count = 0;
+    for (; blw.is_valid(); blw++)
+    {
+        EXPECT_LT(iter_count, (int)(sizeof(expected_screen_columns)/sizeof(expected_screen_columns[0])));
+        EXPECT_EQ(expected_row_offsets[iter_count], blw.row_offset());
+        EXPECT_EQ(expected_screen_columns[iter_count], blw.screen_column());
+        EXPECT_EQ(expected_virtual_columns[iter_count], blw.virtual_column());
+        EXPECT_EQ(expected_character_widths[iter_count], blw.character_width());
+        iter_count++;
+    }
+    EXPECT_EQ((int)strlen(data) + 1, iter_count);
 }
 
 TEST(BufferLineWalkerTest, walks_correctly_with_multi_column_characters_and_line_wrapping)
 {
     static const char data[] = "ab\002xyz\003.";
     std::shared_ptr<Buffer> b = std::make_shared<Buffer>((const uint8_t *)data, strlen(data));
-    BufferLineWalker blw(b, cld);
-    blw.set_width(4);
     std::shared_ptr<Buffer::Iterator> start_of_line = b->add_iterator();
-    int times_called = 0;
-    blw.walk_line(*start_of_line, [&times_called](int row_offset, int screen_column, int virtual_column, int character_width, const Buffer::Iterator & it) -> bool {
-            static int expected_screen_columns[] = {
-                0, 1, 2,  0, 1, 2,  0, 2,  3
-            };
-            static int expected_row_offsets[] = {
-                0, 0, 0,  1, 1, 1,  2, 2,  2
-            };
-            static int expected_virtual_columns[] = {
-                0, 1, 2,  4, 5, 6,  7, 9, 10
-            };
-            static int expected_character_widths[] = {
-                1, 1, 2,  1, 1, 1,  2, 1, 0
-            };
-            EXPECT_LT(times_called, (int)(sizeof(expected_screen_columns)/sizeof(expected_screen_columns[0])));
-            EXPECT_EQ(expected_row_offsets[times_called], row_offset);
-            EXPECT_EQ(expected_screen_columns[times_called], screen_column);
-            EXPECT_EQ(expected_virtual_columns[times_called], virtual_column);
-            EXPECT_EQ(expected_character_widths[times_called], character_width);
-            times_called++;
-            return true;
-    });
-    EXPECT_EQ((int)strlen(data) + 1, times_called);
+    BufferLineWalker blw(b, start_of_line, 4, cld);
+
+    static int expected_screen_columns[] = {
+        0, 1, 2,  0, 1, 2,  0, 2,  3
+    };
+    static int expected_row_offsets[] = {
+        0, 0, 0,  1, 1, 1,  2, 2,  2
+    };
+    static int expected_virtual_columns[] = {
+        0, 1, 2,  4, 5, 6,  7, 9, 10
+    };
+    static int expected_character_widths[] = {
+        1, 1, 2,  1, 1, 1,  2, 1, 0
+    };
+    int iter_count = 0;
+    for (; blw.is_valid(); blw++)
+    {
+        EXPECT_LT(iter_count, (int)(sizeof(expected_screen_columns)/sizeof(expected_screen_columns[0])));
+        EXPECT_EQ(expected_row_offsets[iter_count], blw.row_offset());
+        EXPECT_EQ(expected_screen_columns[iter_count], blw.screen_column());
+        EXPECT_EQ(expected_virtual_columns[iter_count], blw.virtual_column());
+        EXPECT_EQ(expected_character_widths[iter_count], blw.character_width());
+        iter_count++;
+    }
+    EXPECT_EQ((int)strlen(data) + 1, iter_count);
 }
 
 TEST(BufferLineWalkerTest, does_not_push_down_a_row_when_a_multi_column_character_is_wider_than_view_width)
 {
     static const char data[] = "\002\003";
     std::shared_ptr<Buffer> b = std::make_shared<Buffer>((const uint8_t *)data, strlen(data));
-    BufferLineWalker blw(b, cld);
-    blw.set_width(1);
     std::shared_ptr<Buffer::Iterator> start_of_line = b->add_iterator();
-    int times_called = 0;
-    blw.walk_line(*start_of_line, [&times_called](int row_offset, int screen_column, int virtual_column, int character_width, const Buffer::Iterator & it) -> bool {
-            static int expected_screen_columns[] = {
-                0, 0, 0
-            };
-            static int expected_row_offsets[] = {
-                0, 1, 2
-            };
-            static int expected_virtual_columns[] = {
-                0, 2, 4
-            };
-            static int expected_character_widths[] = {
-                2, 2, 0
-            };
-            EXPECT_LT(times_called, (int)(sizeof(expected_screen_columns)/sizeof(expected_screen_columns[0])));
-            EXPECT_EQ(expected_row_offsets[times_called], row_offset);
-            EXPECT_EQ(expected_screen_columns[times_called], screen_column);
-            EXPECT_EQ(expected_virtual_columns[times_called], virtual_column);
-            EXPECT_EQ(expected_character_widths[times_called], character_width);
-            times_called++;
-            return true;
-    });
-    EXPECT_EQ((int)strlen(data) + 1, times_called);
-}
+    BufferLineWalker blw(b, start_of_line, 1, cld);
 
-TEST(BufferLineWalkerTest, stops_iterating_when_callback_returns_false)
-{
-    static const char data[] = "abcdef";
-    std::shared_ptr<Buffer> b = std::make_shared<Buffer>((const uint8_t *)data, strlen(data));
-    BufferLineWalker blw(b, cld);
-    blw.set_width(6);
-    std::shared_ptr<Buffer::Iterator> start_of_line = b->add_iterator();
-    int times_called = 0;
-    blw.walk_line(*start_of_line, [&times_called](int row_offset, int screen_column, int virtual_column, int character_width, const Buffer::Iterator & it) -> bool {
-            times_called++;
-            if (times_called >= 3)
-            {
-                return false;
-            }
-            else
-            {
-                return true;
-            }
-    });
-    EXPECT_EQ(3, times_called);
+    static int expected_screen_columns[] = {
+        0, 0, 0
+    };
+    static int expected_row_offsets[] = {
+        0, 1, 2
+    };
+    static int expected_virtual_columns[] = {
+        0, 2, 4
+    };
+    static int expected_character_widths[] = {
+        2, 2, 0
+    };
+    int iter_count = 0;
+    for (; blw.is_valid(); blw++)
+    {
+        EXPECT_LT(iter_count, (int)(sizeof(expected_screen_columns)/sizeof(expected_screen_columns[0])));
+        EXPECT_EQ(expected_row_offsets[iter_count], blw.row_offset());
+        EXPECT_EQ(expected_screen_columns[iter_count], blw.screen_column());
+        EXPECT_EQ(expected_virtual_columns[iter_count], blw.virtual_column());
+        EXPECT_EQ(expected_character_widths[iter_count], blw.character_width());
+        iter_count++;
+    }
+    EXPECT_EQ((int)strlen(data) + 1, iter_count);
 }
diff --git a/test/src/test_BufferView.cc b/test/src/test_BufferView.cc
index d43dd72..c89421a 100644
--- a/test/src/test_BufferView.cc
+++ b/test/src/test_BufferView.cc
@@ -40,34 +40,34 @@ class MyCharacterWidthDeterminer : public CharacterWidthDeterminer
     }
 } Cwd;
 
-static int LineNumber(const Buffer::Iterator & iterator)
+static int LineNumber(std::shared_ptr<Buffer::Iterator> iterator)
 {
     int line_number = 0;
-    Buffer::Iterator i = iterator;
+    auto i = std::make_shared<Buffer::Iterator>(*iterator);
     for (;;)
     {
-        uint32_t c = *i;
+        uint32_t c = **i;
         if ((c < '0') || (c > '9'))
             break;
         line_number *= 10;
         line_number += ((int)c - '0');
-        i.go_forward();
+        i->go_forward();
     }
     return line_number;
 }
 
-TEST(BufferViewTest, iter_lines_does_not_call_callback_for_empty_buffer)
+TEST(BufferViewTest, does_not_iterate_for_empty_buffer)
 {
     std::shared_ptr<Buffer> b = buffer_empty();
     std::shared_ptr<Buffer::Iterator> iterator = b->add_iterator();
     BufferView bv(b, iterator, Cwd);
     bv.resize(40, 8);
-    int times_called = 0;
-    bv.iter_lines([&times_called](int row_offset, const Buffer::Iterator & iterator) -> bool {
-            times_called++;
-            return true;
-            });
-    EXPECT_EQ(0, times_called);
+    int iter_count = 0;
+    for (auto it = bv.vert_iter(); it.is_valid(); it++)
+    {
+        iter_count++;
+    }
+    EXPECT_EQ(0, iter_count);
     EXPECT_EQ(0, bv.cursor_screen_row());
     EXPECT_EQ(0, bv.cursor_screen_column());
     EXPECT_EQ(0, bv.cursor_virtual_column());
@@ -79,13 +79,13 @@ TEST(BufferViewTest, iterates_through_screen_lines_with_no_wrapping)
     std::shared_ptr<Buffer::Iterator> iterator = b->add_iterator();
     BufferView bv(b, iterator, Cwd);
     bv.resize(40, 8);
-    int times_called = 0;
-    bv.iter_lines([&times_called](int row_offset, const Buffer::Iterator & iterator) -> bool {
-            EXPECT_EQ(times_called, LineNumber(iterator));
-            times_called++;
-            return true;
-            });
-    EXPECT_EQ(8, times_called);
+    int iter_count = 0;
+    for (auto it = bv.vert_iter(); it.is_valid(); it++)
+    {
+        EXPECT_EQ(iter_count, LineNumber(it.iterator()));
+        iter_count++;
+    }
+    EXPECT_EQ(8, iter_count);
     EXPECT_EQ(0, bv.cursor_screen_row());
     EXPECT_EQ(0, bv.cursor_screen_column());
     EXPECT_EQ(0, bv.cursor_virtual_column());
@@ -97,15 +97,15 @@ TEST(BufferViewTest, iterates_through_screen_lines_with_wrapping)
     std::shared_ptr<Buffer::Iterator> iterator = b->add_iterator();
     BufferView bv(b, iterator, Cwd);
     bv.resize(3, 10);
-    int times_called = 0;
+    int iter_count = 0;
     int expected_row_offsets[] = {0, 1, 2, 4, 5, 6, 7};
-    bv.iter_lines([&times_called, &expected_row_offsets](int row_offset, const Buffer::Iterator & iterator) -> bool {
-            EXPECT_EQ(times_called, LineNumber(iterator));
-            EXPECT_EQ(expected_row_offsets[times_called], row_offset);
-            times_called++;
-            return true;
-            });
-    EXPECT_EQ(7, times_called);
+    for (auto it = bv.vert_iter(); it.is_valid(); it++)
+    {
+        EXPECT_EQ(iter_count, LineNumber(it.iterator()));
+        EXPECT_EQ(expected_row_offsets[iter_count], it.row_offset());
+        iter_count++;
+    }
+    EXPECT_EQ(7, iter_count);
     EXPECT_EQ(0, bv.cursor_screen_row());
     EXPECT_EQ(0, bv.cursor_screen_column());
     EXPECT_EQ(0, bv.cursor_virtual_column());
@@ -120,15 +120,15 @@ TEST(BufferViewTest, fills_view_with_last_lines_of_buffer_when_cursor_warps_to_l
     {
     }
     bv.resize(40, 3);
-    int times_called = 0;
+    int iter_count = 0;
     int expected_row_offsets[] = {0, 1, 2};
-    bv.iter_lines([&times_called, &expected_row_offsets](int row_offset, const Buffer::Iterator & iterator) -> bool {
-            EXPECT_EQ(10 + times_called, LineNumber(iterator));
-            EXPECT_EQ(expected_row_offsets[times_called], row_offset);
-            times_called++;
-            return true;
-            });
-    EXPECT_EQ(3, times_called);
+    for (auto it = bv.vert_iter(); it.is_valid(); it++)
+    {
+        EXPECT_EQ(10 + iter_count, LineNumber(it.iterator()));
+        EXPECT_EQ(expected_row_offsets[iter_count], it.row_offset());
+        iter_count++;
+    }
+    EXPECT_EQ(3, iter_count);
     EXPECT_EQ(2, bv.cursor_screen_row());
     EXPECT_EQ(0, bv.cursor_screen_column());
     EXPECT_EQ(0, bv.cursor_virtual_column());