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Postings from August 2010
Ben Morrow wrote: > Quoth pagaltzis@gmx.de (Aristotle Pagaltzis): >> * karl williamson <public@khwilliamson.com> [2010-08-05 19:25]: >>> Aristotle Pagaltzis wrote: >>>> * karl williamson <public@khwilliamson.com> [2010-08-04 15:40]: >>>>> FWIW, I have given this some thought, and came to the >>>>> conclusion that Perl is almost certainly never going to >>>>> change the defaults, because of the backward compatibility >>>>> issues. >>>> Yet you *are* changing the past default right now, *in spite* >>>> of back compat issues… :-) >>> I'm not sure I understand. The default options remain the same. >>> Ben made the point in your quote above that by doing this now >>> when we are pretty much agreed that something should be done >>> will cause this to likely be the last time adding a flag would >>> cause backward compatibility issues. >> If the default is not allowed to change again, then we gain >> nothing from `(?~:)`. > > Right. > >> Right now, the problem is that the default is changing, such that >> `(?-xism)` is not an accurate representation of it. > > Right. > >> This is caused by the fact that we are introducing a flag that >> *requires* a choice of default. >> >> What happens if we run into this situation again in the future? >> >> If the meaning of `(?~:)` is not allowed to change, then it will >> no longer be an accurate representation, so patterns will have to >> stringify to `(?~Xy:)`. > > Wrong. (?~:), with no further flags, means 'The default, whatever that > happens to be in this version of perl'. If we later introduce flags Xy, > Xz and Xw such that one of these must be specified, and Xy is the > default, then (?~:) with no mention of any X* flag will imply Xy. Thus > in > > /foo(?~:bar)baz/Xz > > 'bar' will be matched with /Xy in effect, rather than /Xz. > > (As a separate issue, presumably /Xy in such a case would correspond to > the current semantics, or a bug-fixed version thereof, with /Xz and /Xw > invoking new semantics.) > >> (Personally I would rather skip the entire discussion and train >> people to do >> >> ( my $re_defaults = "" . qr/ / ) =~ s/ //g; >> >> and use *that* instead of hardcoding *either* `(?-xism:)` *or* >> `(?~:)` *or* anything else, because that’s guaranteed to yield >> the right default stringification now and forever.) > > +1. I'm beginning to regret suggesting the idea in the first place... > > Ben > I guess I'll drop this too, as I'm apparently the last person who thinks it is a good idea. The problem with I see in Aristotle's suggestion is that how do people get trained? It's not an obvious solution or we wouldn't have the various cases where things break.Thread Previous | Thread Next