Re: [PATCH 13/16] send-email: extract_valid_address use qr// regexes and /o

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Sep 30, 2010, 18:56 UTC
Message-ID: <AANLkTin_b6eSnHgY2YCOfN7E83gEzrOpktUD3heOnfQw@mail.gmail.com>
In-Reply-To: <7vocbfjg7x.fsf@alter.siamese.dyndns.org>

On Thu, Sep 30, 2010 at 17:25, Junio C Hamano <gitster@pobox.com> wrote:

Show 15 quoted lines

> Jeff King <peff@peff.net> writes:
>
>> ...
>> But we are unnecessarily compiling the sub-regexes each time. Not that
>> this is probably a performance critical piece of code, but your "/o" is
>> doing very little, and this is exactly the sort perl wankery that I find
>> interesting.
>
> Well, isn't the _sole_ point of using qr// to optimize by avoiding
> recompilation?  If this is not a performance critical section of the code,
> what is the point of this change?
>
> This [PATCH 13/16] and also [PATCH 12/16] rewrite strings using qr// but
> the patterns thus compiled are used exactly once before the control leaves
> the scope of the variables, so...

The point is to use Perl's data-types for what they're supposed to be used for. In perl you *can* write:

    my $two = "1" + "1";

To get 2, but that's silly. You should just use integers instead of string coercion:

    my $two = 1 + 1;

Similarly you *can* put regexes in strings, but perl has a first-class datatype for it, so you should do:

    my $rx = qr/foo/;

Not:

    my $rx = "foo";

So it's just a change to use a better style. There are some tangible advantages to using qr// over qq// (also known as ""), e.g. Emacs and Vim will know to highlight the string as a regexp, and when the $rx is interpolated Perl won't need to recompile it because it can just add a pointer to the existing regex in the new pattern.

But the main reason here is to not write code that looks like it targets Perl 5.5, but 5.8.