On Friday, 1 January 2016 at 12:29:01 UTC, anonymous wrote:
On 30.12.2015 12:06, Ivan Kazmenko wrote:
As you can see, bmatch (usage discouraged in the docs) gives
me the
result I want, but match (also discouraged) and matchAll (way
to go) don't.
Am I misusing matchAll, or is this a bug?
The `\1` there is a backreference. Backreferences are not part
of regular expressions, in the sense that they allow you to
describe more than regular languages. [1]
As far as I know, bmatch uses a widespread matching mechanism,
while match/matchAll use a different, less common one. It
wouldn't surprise me if match/matchAll simply didn't support
backreferences.
Backreferences are not documented, as far as I can see, but
they're working in other patterns. So, yeah, this is possibly a
bug.
[1]
https://en.wikipedia.org/wiki/Regular_expression#Patterns_for_non-regular_languages
The overview by the module author
(http://dlang.org/regular-expression.html) does mention in the
last paragraph that backreferences are supported. Looks like it
is a common feature in other programming languages, too.
The "\1" part is working correctly when "abab" or "abxab" or
"ababx" but not "abac". This means it is probably intended to
work, and handling "xabab" incorrectly is a bug.
Also, as I understand it from the docs, matchAll/matchFirst use
the most appropriate of match/bmatch internally, so if match does
not properly support the particular backreference but bmatch
does, the bug is in using the incorrect one to handle a pattern.
At any rate, wrong result with a 8-character pattern produces a
"regex don't work" impression, and I hope something can be done
about it.
