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Re: need sort help

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From:
Brandon Allbery
Date:
June 9, 2018 19:01
Subject:
Re: need sort help
Message ID:
CAKFCL4UsdBcBYmbwMBSuwCO4VKBhWi8jU8Yt=PvPFXciRRe6Mw@mail.gmail.com
The ".=" operator means call the method on the right, with the thing on the
left as invocant, and assign the result back to the thing on the left. So

    @x .= sort: ...

is the same as

    @x = @x.sort(...)

So you're being confused by the syntactic "magic" of ".=".

On Sat, Jun 9, 2018 at 2:58 PM Xin Cheng <xincheng99@gmail.com> wrote:

> I got the point for //.
>
> Another question is about calling the method sort with a code block. I can
> understand
>
> @x .= sort({ ... });
>
> But I don't quite understand why this form also works.
>
> @x .= sort: { ... };
>
> I look into the documentation for infix ":",
> https://docs.perl6.org/routine/: , and it explains something like this:
>
> Used as an argument separator just like infix , and marks the argument to
> its left as the invocant. That turns what would otherwise be a function
> call into a method call.
>
> substr('abc': 1);       # same as 'abc'.substr(1)
> Infix : is only allowed after the first argument of a non-method call. In
> other positions, it's a syntax error.
>
>
> How does the above explanation related to the case in hand @x .= sort: {
> ... }; ? Is sort an invocant? Or I miss something.
>
> Regards
>
> Xin
>
>
>
> On Jun 9, 2018, at 12:44 PM, Brandon Allbery <allbery.b@gmail.com> wrote:
>
> More precisely, at that point you have a bunch of numbers, but possibly
> not as many as expected if some of the components weren't numeric (or all
> of them, as when there are files present that aren't the expected logs).
> Which means some or all of those variables will be undefined instead of
> numbers. The // replaces those with the following value (0), so they do
> something sensible when sorted instead of producing warnings.
>
> On Sat, Jun 9, 2018 at 11:40 AM Xin Cheng <xincheng99@gmail.com> wrote:
>
>> This is very interesting. But I wonder how it works. I can understand the
>> first line
>>
>>  my ($month, $day, $year, $hour, $minute, $second) = .comb(/\d+/);
>>
>> Which extract the variables from $_. What is the second line doing, it is
>> very concise.
>>
>>  ($year // 0, $month // 0, $day // 0, $hour // 0, $minute // 0,
>> $second // 0, $_);
>>
>> Could somebody explain in some more words.? What does  // do? Why it
>> sorts the array?
>>
>> Regards
>>
>> Xin
>>
>> On Jun 9, 2018, at 12:51 AM, Timo Paulssen <timo@wakelift.de> wrote:
>>
>> That's unnecessarily long and complicated, here's how you can do it much
>> easier:
>>
>>     @x.sort: {
>>         my ($month, $day, $year, $hour, $minute, $second) = .comb(/\d+/);
>>         ($year // 0, $month // 0, $day // 0, $hour // 0, $minute // 0,
>> $second // 0, $_);
>>     }
>>
>> Trying it on some input data:
>>
>>     cimtrak.log.06-08-2018_16:07:39.zip
>>     cimtrak.log.06-08-2018_17:07:39.zip
>>     cimtrak.log.07-08-2018_06:07:39.zip
>>     cimtrak.log.07-08-2018_16:07:39.zip
>>     cimtrak.log.12-08-2016_06:07:39.zip
>>     cookies
>>     asbestos
>>     fire engine
>>     perl6
>>     butterflies
>>
>> results in:
>>
>>     asbestos
>>     butterflies
>>     cookies
>>     fire engine
>>     perl6
>>     cimtrak.log.12-08-2016_06:07:39.zip
>>     cimtrak.log.06-08-2018_16:07:39.zip
>>     cimtrak.log.06-08-2018_17:07:39.zip
>>     cimtrak.log.07-08-2018_06:07:39.zip
>>     cimtrak.log.07-08-2018_16:07:39.zip
>>
>> This is the schwartzian transform that was mentioned in another mail.
>> why it wasn't actually shown, i have no clue :)
>>
>> Hope that helps
>>   - Timo
>>
>>
>>
>
> --
> brandon s allbery kf8nh                               sine nomine
> associates
> allbery.b@gmail.com
> ballbery@sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad
> http://sinenomine.net
>
>
>

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b@gmail.com                                  ballbery@sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net

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