Besides memory use I'm not sure why his approach isn't easy for everything you suggested.
Want to group undo actions? It's pretty easy to define arbitrary grouping algorithms on the sequence of recent state snapshots, which yields...a smaller sequence of state snapshots :-) a nice composeable idea.
To show redo after an undo, store recent undo triggers in the state, and if there is undo in current state, show redo with a list of older mem states to jump to. This repr also makes it easy to wipe out redos when doing a redo-breaking operation like editing the doc.
Memory use can indeed become a problem. But if/when it does, there is probably some obvious trait of the sequence of recent states that makes it easy to compress. Like for example that it's 99% the same contents, after a small edit. Or that one edit type dominates. Or that folks don't often care if they can't Ctrl+Z through 8GB of typing.
I think most programmers would gain by not dismissing simple approaches out of hand as too simple.
If writing it off for memory, write out the math for the size of the state and the allotted memory. This is not the era of computers that our languages were invented in; the page size your CPU fetches from insanely fast SSDs can be 4kb. And it can do a lot of that in a blink. Trying to shift runtime work (that the computer does) back to compile/design time (that the dev does) can cripple a system's performance in the short run (for coding/delivery time) and long run (for performance after pointer chasing)...luckily most of the time it doesn't matter anyway :-)
Want to group undo actions? It's pretty easy to define arbitrary grouping algorithms on the sequence of recent state snapshots, which yields...a smaller sequence of state snapshots :-) a nice composeable idea.
To show redo after an undo, store recent undo triggers in the state, and if there is undo in current state, show redo with a list of older mem states to jump to. This repr also makes it easy to wipe out redos when doing a redo-breaking operation like editing the doc.
Memory use can indeed become a problem. But if/when it does, there is probably some obvious trait of the sequence of recent states that makes it easy to compress. Like for example that it's 99% the same contents, after a small edit. Or that one edit type dominates. Or that folks don't often care if they can't Ctrl+Z through 8GB of typing.
I think most programmers would gain by not dismissing simple approaches out of hand as too simple.
If writing it off for memory, write out the math for the size of the state and the allotted memory. This is not the era of computers that our languages were invented in; the page size your CPU fetches from insanely fast SSDs can be 4kb. And it can do a lot of that in a blink. Trying to shift runtime work (that the computer does) back to compile/design time (that the dev does) can cripple a system's performance in the short run (for coding/delivery time) and long run (for performance after pointer chasing)...luckily most of the time it doesn't matter anyway :-)