It sounds confusing, but it’s actually really easy to get used and hard to walk away from it. Essentially the undo is just another operation so it can be undone just like everything else, and that’s a redo. Imagine the following situation, I wrote a text, but wasn’t happy with some part, so I select that part and delete it, now I keep writing but I realised I need some part of what was there, so I undo all of the text that I wrote, select the text I want to copy, and accidentally cut it instead of copy it. In most editors that’s it, you’re fucked, you just lost your most recent changes, on Emacs undo does not destroy things, it only adds to the sequence. In other words, as a step by step:
Write text
Delete part of it
Write more text
Undo step 3 (most editors that means go back to step 2, so step 4 is in a dangerous space)
Undo step 2 (again, most editors would have actually gone to step 2)
You’re now in something that looks like step 2, cut the text you wanted (on most editors because you were in step 2 and did changes you can’t ever go back to step 4, because this is the new step 3 and there isn’t still a step 4, so undo and redo will undo and redo the cut of that text)
Undo step 6 (you’re now similar to how you started step 6 or 2, on most editors you are really on step 2).
Undo again (on most editors that would take you to step 1), this will take you to step 5, i.e. you redid the step 2, so the text disappeared and you’re like you were at the beginning of step 3.
Undo again and you undo the undo of step 3, putting you back on original step 4
Like I said, confusing to understand, but it means that you can’t ever shoot yourself in the foot by undoing things.
Emacs’s undo-tree – which I mentioned above that I use – also provides non-destructive undo, same as emacs’s base undo. So you can’t lose data by undoing things. However, it also uses the undo and redo semantics to traverse one branch of the tree, so it works like most other apps as long as you aren’t needing to recover data that would normally have been “lost” by performing an undo.
There are probably faster ways to do it, but since I rarely need to quickly grab stuff that an undo destroyed, I haven’t looked into them.
Do non-undo operation.
Undo it.
Do non-undo operation. At this point, in software packages that lack non-destructive undo, you will have lost the data in #1.
Run undo-tree-visualize, on C-x u by default. A new window will come up displaying the undo history as a tree.
You can traverse around the tree. Move to the node immediately before the branch that you abandoned, and use C-b and C-f to switch between branches.
I will bet that vim has some form of non-destructive undo as well. Might take an add-on package, but generally-speaking, useful behavior in emacs and vim tend to get ported to each other.
In Vim, every time you press u and then make a different change, Vim stores the previous state’s text by creating an “undo branch”. In this example, after you typed “two”, then pressed u, then typed “three”, you created an leaf branch that stores the state containing the text “two”. At that moment, the undo tree contained at least two leaf nodes: the main node containing the text “three” (most recent) and the undo branch node containing the text “two”. If you had done another undo and typed the text “four”, you would have at three nodes: a main node containing the text “four” and two nodes containing the texts “three” and “two”.
To traverse each undo tree nodes, you can use g+ to go to a newer state and g- to go to an older state. The difference between u, Ctrl-R, g+, and g- is that both u and Ctrl-R traverse only the main nodes in undo tree while g+ and g- traverse all nodes in the undo tree.
Undo tree is not easy to visualize. I find vim-mundo plugin to be very useful to help visualize Vim’s undo tree. Give it some time to play around with it.
It sounds like vim+vim-mundo and emacs+undo-tree operate kind of similarly, actually.
It sounds confusing, but it’s actually really easy to get used and hard to walk away from it. Essentially the undo is just another operation so it can be undone just like everything else, and that’s a redo. Imagine the following situation, I wrote a text, but wasn’t happy with some part, so I select that part and delete it, now I keep writing but I realised I need some part of what was there, so I undo all of the text that I wrote, select the text I want to copy, and accidentally cut it instead of copy it. In most editors that’s it, you’re fucked, you just lost your most recent changes, on Emacs undo does not destroy things, it only adds to the sequence. In other words, as a step by step:
Like I said, confusing to understand, but it means that you can’t ever shoot yourself in the foot by undoing things.
Emacs’s
undo-tree– which I mentioned above that I use – also provides non-destructive undo, same as emacs’s base undo. So you can’t lose data by undoing things. However, it also uses theundoandredosemantics to traverse one branch of the tree, so it works like most other apps as long as you aren’t needing to recover data that would normally have been “lost” by performing an undo.There are probably faster ways to do it, but since I rarely need to quickly grab stuff that an undo destroyed, I haven’t looked into them.
Do non-undo operation.
Undo it.
Do non-undo operation. At this point, in software packages that lack non-destructive undo, you will have lost the data in #1.
Run
undo-tree-visualize, onC-x uby default. A new window will come up displaying the undo history as a tree.You can traverse around the tree. Move to the node immediately before the branch that you abandoned, and use
C-bandC-fto switch between branches.Yeah, no.
If ‘esc-u’ doesn’t work, I :q!
,
I will bet that vim has some form of non-destructive undo as well. Might take an add-on package, but generally-speaking, useful behavior in emacs and vim tend to get ported to each other.
googles
Yup.
https://learnvim.irian.to/basics/undo
It sounds like vim+vim-mundo and emacs+undo-tree operate kind of similarly, actually.
EDIT: In fact, this is definitely the case. According to emacswiki, emacs’ undo-tree is based on vim’s model.
Nice.
you mean
ZQNope! But cool.