[whatwg] Fixing undo on the Web - UndoManager and Transaction

[Annie Sullivan]

On Tue, Aug 9, 2011 at 4:59 PM, Jonas Sicking <jonas at sicking.cc> wrote:

> On Tue, Aug 9, 2011 at 12:03 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:
>
> > On Tue, Aug 9, 2011 at 1:17 AM, Jonas Sicking <jonas at sicking.cc> wrote:
> >
> >> On Tue, Aug 9, 2011 at 12:42 AM, Ryosuke Niwa <rniwa at webkit.org> wrote:
> >> > On Tue, Aug 9, 2011 at 12:31 AM, Jonas Sicking <jonas at sicking.cc>
> >> wrote:
> >>  >> Likewise I still haven't heard of any examples where the
> >> apply function
> >> >> isn't simply init+reapply. So it still seems better to me to have a
> >> >> init/apply/unapply split rather than a apply/reapply/unapply split.
> >> >
> >> > This is also pending for developer feedback.
> >>
> >
> > I've talked about this with Alex, and we both agreed that having
> > apply/reapply split is cleaner because in many cases you'd like to know
> > whether you're in redo or not.  i.e. more work is done in reapply than in
> > apply.
> >
>
> Could you please provide examples. I feel like I'm fighting an elusive
> shadow.
>
> I.e. please provide an example where "apply" isn't just init+reapply.
> "There
> are many cases" isn't a particularly compelling argument unless you can
> show
> these cases :-)
>
> And ideally also some estimate how common that case will be compared to
> "apply" simply being init+reapply. This is important since if that is very
> rare, people can always implement it themselves using init+reapply
> semantics
> by having a flag on the object which indicates if you're in the first call
> or not.


As an author, I would really love to have as much information as possible
about what the user was trying to do. I might want to keep my own
bookkeeping about what is going on in the document, in some other format
besides HTML.

For example, if I were writing a collaborative editing app, and I decided
that any user could unapply/reapply any change, I might end up with a
sequence like this:

Susan made change X
Bob unapplied change X
Susan reapplied change X
Bob unapplied change X
Susan reapplied change X
...

It would be great to show that in the document history view of my app very
clearly. I think knowing that a change was unapplied/reapplied instead of
just showing text diffs between revisions would be great.

-Annie