We were just pointing out that changing "startGAP" to "GAPstart" is doing extra work; it's just as good to end up with "stastart"; we don't care what's in the bytes that you're writing as "GAP". The location of the gap is typically represented with a couple of pointers or ints.
Which didn't help your point. You don't care what is in the gap. But you do care what is in either side of it. So, you have to move those.
Edit:. Curse my phone typing. I am still contemplating this and see roughly what you are getting at. Didn't mean to post. I do challenge some of this. But still thinking. Apologies for posting early.
Edit2: on the assumption that I don't care what is in the gap,i think I fully agree with you and I was wrong. I challenge that some, but would have to think longer. Basically, my challenge is that undo and redo are more than a bit easier if you take care of the contents of the gap.
Here's a gap buffer in Lua. The code for inserting and deleting: https://github.com/darius/dole/blob/master/text.lua#L171
(The representation is documented at the start of the file. Some of the code in this function is only for assertions.)
The part that moves the gap is https://github.com/darius/dole/blob/master/text.lua#L178 and it's just a memmove. There's nothing like the permutation algorithm Bentley wrote about, his rotating by double reversal. If I'm missing your point, I'm sorry this is so troublesome -- maybe it's not worth the bother of correcting me.
(Added: I wrote the above before your edit. I hope this helps; probably there are better sources to read, but I picked this one because I wrote it.)
Yeah, apologies for the edits. I meant to hold on the thought some last time.
And it is absolutely no bother. Thanks for discussing it! Again, I would never dream of this as an interview thing. Fun discussion, though.
Some day I may dive into a text editor. Many of the data structures that are supposedly used there don't leap to me as obvious wins nowadays. They often pass the"appealing argument" test, but I have grown very weary of that.
