Your proposal for look-behind relies on being able to count the match length of the look-behind in order to step back that far. This presupposes that atoms like . and character classes have a fixed length.
However, with the /u flag, the . and some character classes can be either 1 or two code units. This means you don't know how far to step back. This needs to be fixed in a way that is not incompatible with the "correct" .NET way of doing things. Eg matching /a.(?<!x..)/ against "xa😹" (x, a, cat-face-with-tears-of-joy, which is a surrogate pair). The back reference has an apparent width of 3, so we step back 3 code units, but that hits the 'a', not the 'x' and so the back reference fails to spot the 'x'. On Sun, Oct 4, 2015 at 1:52 PM, Nozomu Katō <[email protected]> wrote: > Apparently my proposal for adding the look-behind assertions to RegExp > has been in trouble. I would like to ask anyone for help. > > The following story is what I know about the proposal after my previous > post: > > I created a pull request for the proposal in July and sent an email to > Brendan Eich asking if I can put his name as a champion: > https://github.com/tc39/ecma262/pull/48 > > I have not received a reply to my email, but I received a notification > email in September that replying to the pull request, the proposal was > moved to stage 0. Today, however, I just noticed that the proposal had > been dropped from stage 0, stating "RegExp lookbehind has no champion". > https://github.com/tc39/ecma262/commits/master/stage0.md (Oct 4, 2015) > > I am uncertain about what happened. Does this mean that Brendan Eich is > no longer a champion or did not take a champion on from the beginning or > ...? > > > Regards, > Nozomu > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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