[jmull]

The big advantage to mapping is that you only read from disk the portions of the file you need, and only when you need them. Disk access is monumentally slow, so this can be a big win: if you don’t need to access all of a large file, or don’t need to access it all at once, mapping saves you very expensive operations or spreads them out over time.

The problem with that for a text editor is that probably the first thing you want to do is process the line endings. So you’re just going to access the entire file, right away, as fast as possible anyway.

So mapping doesn’t really give an advantage in this case.