Comment 1:

As far as I can tell the character classes do work by default, even though the default
is Perl mode.  Can you show an example of a failing program?

Status changed to WaitingForReply.

Comment 2 by steven.hartland@multiplay.co.uk:

Here's an example:
http://play.golang.org/p/uX83Si_90p
The output is:
Match by Set (Perl): true
Match by Class (Perl): false
Match by Class (POSIX): true
So the character class, in this case [:xdigit:] only works in POSIX mode not in Perl mode

Comment 3 by steven.hartland@multiplay.co.uk:

Here's an example:
http://play.golang.org/p/uX83Si_90p
The output is:
Match by Set (Perl): true
Match by Class (Perl): false
Match by Class (POSIX): true
So the character class, in this case [:xdigit:], only works in POSIX mode not in Perl
mode

Comment 4:

I'm sorry, I don't understand how your test case demonstrates that.  What I'm looking
for is a test case where you use the same regexp for Compile and CompilePOSIX, but get
different results.
What your test case appears to demonstrate is that [:xdigit:] is not equivalent to
[0-9A-Fa-f], which may be a bug but is not the same as the bug you are reporting.

Comment 5 by steven.hartland@multiplay.co.uk:

Sorry, that was a cut and paste error, which caused my initial confusion as to the real
nature of the issue.
On further investigation it appears that the actual problem is that "named" ASCII
Character classes can only be used within a character class.
So if you want to match an xdigit you must use [[:xdigit:]] and not just [:xdigit:]
Example:
http://play.golang.org/p/iGziut5Vi6
The confusion comes from regexp/syntax docs where in the "Single characters:" block at
the top it lists items such as:
\d             Perl character class
[:alpha:]      ASCII character class
\d can be used directly in a regexp but apparently not so for named ASCII character
classes such as [:alpha:]
Additionally in the docs there is:
Perl character classes:
\d             digits (== [0-9])
...
ASCII character classes:
[:digit:]      digits (== [0-9])
Here we see the Perl character class \d, which can be used directly, documented as being
identical to the ASCII character class [:digit:] which can not be used directly and
needs enclosing []'s
An example of this is:
http://play.golang.org/p/240L99E6F4
In Stefan Schroeder's Golang Regex Tutorial:
https://github.com/StefanSchroeder/Golang-Regex-Tutorial/blob/master/01-chapter1.markdown
He clearly states this quirk of ASCII Character classes with: "Note that you have to
wrap an ASCII character class in []. "
Hope this clarifies the issue and sorry again for my initial inaccurate report.

Comment 6:

Thanks for sorting this out.  I agree that the docs seem rather misleading by listing
[:alpha:] as a single character, when in fact it can only appear in a character class.

Labels changed: added repo-main, release-go1.4.

Status changed to Accepted.

Comment 7:

Thanks. This is also re2 issue #116.

Comment 8:

CL https://golang.org/cl/155890043 mentions this issue.

Comment 9:

This issue was closed by revision 85fd0fd.

Status changed to Fixed.