From: "David A. Black" <dblack@...>
Date: 2008-11-29T22:13:55+09:00
Subject: [ruby-core:20165] Re: \Z? in regular expression in 1.9.1

Hi --

On Sat, 29 Nov 2008, Yukihiro Matsumoto wrote:

> Hi,
>
> In message "Re: [ruby-core:20162] Re: \Z? in regular expression in 1.9.1"
>    on Sat, 29 Nov 2008 19:42:09 +0900, "=?ISO-8859-2?Q?Rados=B3aw_Bu=B3at?=" <radek.bulat@gmail.com> writes:
>
> |> Could someone shed some light on whether it is 1.9.1 engine restriction,
> |> general regular expressions
> |> restriction or possible 1.9.1 bug?
> |>
> |> Just in case: this regexp comes from autospec in RSpec.
> |
> |I think this is expected behavior. "\Z" is zero width assertion so it
> |doesn't make sense to mix it with "?" operator. Your regexp is the
> |same as:
> | /\n(\.\/)?(.*spec\.rb):[\d]+:/
>
> That's right.  But perhaps we should allow repeat quantifier after
> anchors since Perl and old Ruby does.

Does it make sense, though, for zero-width assertions? It's like
saying: this either is, or isn't, the end of the string, which is
always true. Or this either is, or isn't, a word boundary, etc.

Also, it's not allowed unconditionally in 1.8:

>> /\Z?/
SyntaxError: compile error
(irb):5: invalid regular expression; there's no previous pattern, to
which '?' would define cardinality at 3: /\Z?/

I think it groups the anchor with whatever comes right before it, and
that's the target for the quantifier.

>> /a\Z?/.match("bcde").to_a
=> [""]

I guess that's harmless but I can't think of any use for it.


David

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