Re: [PATCH] git-remote-mediawiki: Fix a bug in a regexp

From: Eric Sunshine <sunshine@sunshineco.com>
Date: Jun 9, 2013, 05:21 UTC
Message-ID: <CAPig+cSCLsMQ3Xg9UKury41G0vHddnL1PVKBJL_N2amA9e0eyQ@mail.gmail.com>
In-Reply-To: <20130609025708.GB30393@sigill.intra.peff.net>

On Sat, Jun 8, 2013 at 10:57 PM, Jeff King <peff@peff.net> wrote:

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> On Sat, Jun 08, 2013 at 08:38:56PM +0200, Matthieu Moy wrote:
>
>> Célestin Matte <celestin.matte@ensimag.fr> writes:
>>
>> > In Perl, '\n' is not a newline, but instead a literal backslash followed by an
>> > "n". As the output of "rev-list --first-parent" is line-oriented, what we want
>> > here is a newline.
>>
>> This is right, but the code actually worked the way it was. I'm not
>> sure, but my understanding is that '\n' is the string "backslash
>> followed by n", but interpreted as a regexp, it is a newline.
>
> Yes, the relevant doc (from "perldoc -f split") is:
>
>   The pattern "/PATTERN/" may be replaced with an expression to specify
>   patterns that vary at runtime.  (To do runtime compilation only once,
>   use "/$variable/o".)
>
> So it is treating "\n" as an expression and compiling the regex each
> time through ...

I read this as saying only that static /PATTERN/ can also be a composed /$PATTERN/. It does not indicate how string 'PATTERN' is treated, nor does any other part of "perldoc -f split" make special mention of string 'PATTERN'. In fact, the only explanation I found regarding string 'PATTERN' is in my Camel book (3rd edition, page 796) in a parenthesized comment:

    (... if you supply a string instead of a regular expression, it'll be
    interpreted as a regular expression anyway.)

Show 11 quoted lines

>> The new code looks better than the old one, but the log message may be
>> improved.
>
> Agreed. I think the best explanation is something like:
>
>   Perl's split function takes a regex pattern argument. You can also
>   feed it an expression, which is then compiled into a regex at runtime.
>   It therefore works to pass your pattern via single quotes, but it is
>   much less obvious to a reader that the argument is meant to be a
>   regex, not a static string. Using the traditional slash-delimiters
>   makes this easier to read.

Sounds good to me.