MRAB:
The disadvantage there is that when you move the cursor you must move characters around. For example, what if the cursor was at the start and you wanted to move it to the end? Also, when the gap has been filled, you need to make a new one.
The normal technique is to only move the gap when text is added or removed, not when the cursor moves. Code that reads the contents, such as for display, handles the gap by checking the requested position and using a different offset when the position is after the gap.
Gap buffers work well because changes are generally close to the previous change, so require moving only a relatively small amount of text. Even an occasional move of the whole contents won't cause too much trouble for interactivity with current processors moving multiple megabytes per millisecond.
Neil -- http://mail.python.org/mailman/listinfo/python-list
