* 1 Fedora Weekly News Issue 269
o 1.1 Announcements
+ 1.1.1 Fedora Announcement News
# 1.1.1.1 Changes to the Packaging Guidelines
+ 1.1.2 Fedora Development News
# 1.1.2.1 Beta change freeze
# 1.1.2.2 Fedora 15 schedule to slip an additional week
+ 1.1.3 Fedora Events
# 1.1.3.1 Upcoming Events (March - May 2011)
# 1.1.3.2 Past Events
# 1.1.3.3 Additional information
o 1.2 Fedora In the News
+ 1.2.1 Red Hat Proves That Open Source Is Good for Business
(PC World)
o 1.3 Ambassadors
+ 1.3.1 Welcome New Ambassadors
+ 1.3.2 Summary of traffic on Ambassadors mailing list
+ 1.3.3 Summary of events reported on Ambassadors mailing list
+ 1.3.4 Summary of traffic on FAmSCo mailing list
o 1.4 QualityAssurance
+ 1.4.1 Test Days
+ 1.4.2 Anaconda testing
+ 1.4.3 GNOME Tweak Tool testing
+ 1.4.4 Fedora 15 Beta preparation
+ 1.4.5 Improving pre-release download page
o 1.5 Security Advisories
+ 1.5.1 Fedora 15 Security Advisories
+ 1.5.2 Fedora 14 Security Advisories
+ 1.5.3 Fedora 13 Security Advisories
o 1.6 LATAM Fedora!
+ 1.6.1 Ruby Capítulo 2 : Una clase algo más completa
# 1.6.1.1 Constantes vs variables
# 1.6.1.2 El poder de herencia
# 1.6.1.3 Espacios de nombres
# 1.6.1.4 Herencia múltiples vs Mixins
* 1.6.1.4.1 mixin_module.rb
- Fedora Weekly News Issue 269 -
Welcome to Fedora Weekly News Issue 269[1] for the week ending March 30, 2011.
What follows are some highlights from this issue.
This issue begins with announcements from the Fedora Project, including changes
to the packaging guidelines and an additional week slip of the Fedora 15
release date. One article for Fedora In the News this week from PC World on
Red Hat's financial success. In Ambassador news, details on new members of the
team, a summary of discussion on the Ambassador and FAmSCo lists, and a couple
event reports. In Quality Assurance news, details on the latest and upcoming
Test Days on power management, printing and ABRT, as well as various reports
leading up to the Fedora 15 beta release. Security Advisories brings us current
with the security-related package releases this past week for Fedora 13, 14 and
15, and in our Latin American beat this week, a second installment of Guillermo
Gomez's Ruby Primer, in Spanish. Enjoy!
An audio version of some issues of FWN - FAWN - are available! You can listen
to existing issues[2] on the Internet Archive. If anyone is interested in
helping spread the load of FAWN production, please contact us!
If you are interested in contributing to Fedora Weekly News, please see our
'join' page[3]. We welcome reader feedback: [email protected]
FWN Editorial Team: Pascal Calarco, Adam Williamson
1. ↑ http://fedoraproject.org/wiki/FWN/Issue269
2. ↑ http://www.archive.org/search.php?query=subject%3A%22FWN%22
3. ↑ http://fedoraproject.org/wiki/NewsProject/Join
-- Announcements --
In this section, we cover announcements from the Fedora Project, including
general announcements[1], development announcements[2] and Events[3].
Contributing Writer: Pascal Calarco
1. ↑ http://lists.fedoraproject.org/pipermail/announce/
2. ↑ http://lists.fedoraproject.org/pipermail/devel-announce/
3. ↑ http://fedoraproject.org/wiki/Events
--- Fedora Announcement News ---
The announcement list is always exclusive for the Fedora Community. Please,
visit the past announcements at[1]
1. ↑ https://admin.fedoraproject.org/mailman/listinfo/announce
---- Changes to the Packaging Guidelines ----
Tom 'Spot' Callaway announced[1],
"Here are the changes to the Fedora Packaging Guidelines for this week:
The Packaging:PHP guidelines have been updated to reflect that PEAR
documentation provided by upstream are installed in %{pear_docdir}, should stay
there, and must be marked as %doc.
Additionally, the definition of pear_docdir has been defined as %{_docdir}/pear.
https://fedoraproject.org/wiki/Packaging:PHP
---
The Java guidelines have been updated to add information and sample template
for Maven 3 (Fedora 15+).
https://fedoraproject.org/wiki/Packaging:Java
---
These guidelines (and changes) were approved by the Fedora Packaging Committee
(FPC).
Many thanks to Remi Collet, Stanislav Ochotnicky, and all of the members of the
FPC, for assisting in drafting, refining, and passing these guidelines.
As a reminder: The Fedora Packaging Guidelines are living documents! If you
find something missing, incorrect, or in need of revision, you can suggest a
draft change. The procedure for this is documented here [2]
Thanks,
~spot"
1. ↑ http://lists.fedoraproject.org/pipermail/announce/2011-March/002942.html
2. ↑
http://fedoraproject.org/wiki/Packaging/Committee#GuidelineChangeProcedure
--- Fedora Development News ---
The Development Announcement[1] list is intended to be a LOW TRAFFIC
announce-only list for Fedora development.
Acceptable Types of Announcements
* Policy or process changes that affect developers.
* Infrastructure changes that affect developers.
* Tools changes that affect developers.
* Schedule changes
* Freeze reminders
Unacceptable Types of Announcements
* Periodic automated reports (violates the INFREQUENT rule)
* Discussion
* Anything else not mentioned above
1. ↑ https://admin.fedoraproject.org/mailman/listinfo/devel-announce
---- Beta change freeze ----
Dennis Gilmore announced[1],
"Hi All a heads up that change freeze for the Fedora 15 Beta is Tuesday April
5th. After this point only accepted blocker bugs will be pulled in. Please
limit your changes to try and avoid unintended breakages.
thanks
Dennis"
1. ↑
http://lists.fedoraproject.org/pipermail/devel-announce/2011-March/000773.html
---- Fedora 15 schedule to slip an additional week ----
Jared K. Smith announced[1]
"The Fedora 15 development cycle is well under way, and making good progress.
Yesterday I met[1] with Release Engineering, QA, the Fedora Program Manager,
and we decided that in order to accommodate some late-breaking changes, we're
going to need to slip the Fedora 15 release schedule by a week in order to have
adequate time to do proper testing of the candidate images before the Beta.
This slip will affect the entire Fedora 15 development cycle, as shown in the
chart below:
o F15 Devel Start 2010-11-02
o Feature Submission Deadline 2011-01-25
o Feature Freeze 2011-02-08
o Branch From Rawhide 2011-02-08
o Software String Freeze 2011-02-15
o Alpha Change Deadline 2011-02-15
o Alpha Release 2011-03-08
N O W -----------------------
o Software Translation Deadline 2011-04-05
o Beta Change Deadline 2011-04-05
o Features 100% Complete 2011-04-05
o Beta Release 2011-04-19
o Final Change Deadline 2011-05-09
o Compose RC 2011-05-10
o GA 2011-05-24
Robyn Bergeron has also kindly updated the complete break-out of the Fedora
release schedule, which is available[2]. If you have any questions or concerns,
please don't hesitate to let me know.
-- Jared Smith Fedora Project Leader "
1. ↑
http://lists.fedoraproject.org/pipermail/devel-announce/2011-March/000772.html
2. ↑ http://rbergero.fedorapeople.org/schedules/f-15/
--- Fedora Events ---
The purpose of event is to build a global Fedora events calendar, and to
identify responsible Ambassadors for each event. The event page is laid out by
quarter and by region. Please maintain the layout, as it is crucial for budget
planning. Events can be added to this page whether or not they have an
Ambassador owner. Events without an owner are not eligible for funding, but
being listed allows any Ambassador to take ownership of the event and make it
eligible for funding. In plain words, Fedora events are the exclusive and
source of marketing, learning and meeting all the fellow community people
around you. So, please mark your agenda with the following events to consider
attending or volunteering near you!
---- Upcoming Events (March - May 2011) ----
* North America (NA)[1]
* Central & South America (LATAM): [2]
* Europe, Middle East, and Africa (EMEA)[3]
* India, Asia, Australia (India/APJ)[4]
1. ↑ http://fedoraproject.org/wiki/Events#FY12_Q1_.28March_2011_-_May_2011.29
2. ↑
http://fedoraproject.org/wiki/Events#FY12_Q1_.28March_2011_-_May_2011.29_2
3. ↑
http://fedoraproject.org/wiki/Events#FY12_Q1_.28March_2011_-_May_2011.29_3
4. ↑
http://fedoraproject.org/wiki/Events#FY12_Q1_.28March_2011_-_May_2011.29_4
---- Past Events ----
Archive of Past Fedora Events[1]
1. ↑ http://fedoraproject.org/wiki/FedoraEvents/PastEvents
---- Additional information ----
* Reimbursements -- reimbursement guidelines.
* Budget -- budget for the current quarter (as distributed by FAMSCo).
* Sponsorship -- how decisions are made to subsidize travel by community
members.
* Organization -- event organization, budget information, and regional
responsibility.
* Event reports -- guidelines and suggestions.
* LinuxEvents -- a collection of calendars of Linux events.
-- Fedora In the News --
In this section, we cover news from the trade press and elsewhere that is
re-posted to the Fedora Marketing list[1].
http://fedoraproject.org/wiki/Marketing
Contributing Writer: Pascal Calarco
1. ↑ http://lists.fedoraproject.org/pipermail/marketing/
--- Red Hat Proves That Open Source Is Good for Business (PC World) ---
Rahul Sundaram forwarded[1] a posting on Red Hat's financial success:
"Critics of free and open source software are fond of making the argument that
software must be locked up, patented and jealously guarded if it is to serve as
the basis for a successful business. Well, Red Hat just refuted such claims in
a big way this week with its fourth quarter earnings report, which blew away
analysts' expectations and placed the company well on track for billion-dollar
revenues in the upcoming year."
Based in North Carolina, Red Hat is the company behind both the Fedora and the
Red Hat Enterprise Linux (RHEL) Linux distributions. Fedora is the free,
community version of the software, while RHEL is sold as acommercial product
with support and services."
The full article is available[2].
1. ↑
http://lists.fedoraproject.org/pipermail/marketing/2011-March/013758.html
2. ↑
http://www.pcworld.com/businesscenter/article/223346/red_hat_proves_that_open_source_is_good_for_business.html
-- Ambassadors --
This section covers the news surrounding the Fedora Ambassadors Project[1].
Contributing Writer: Sankarshan Mukhopadhyay
1. ↑ http://fedoraproject.org/wiki/Ambassadors
--- Welcome New Ambassadors ---
This week the Fedora Ambassadors Project had a couple of new members joining.
Everton Cardoso from Brazil mentored by Daniel Bruno
--- Summary of traffic on Ambassadors mailing list ---
Christoph Wickert raised [1] some questions regarding the budget [2] Max
Spevack provided [3] actual figures from the expenses. David Nalley mentioned
[4] that some of the issues raised in the mail were also part of the Board IRC
meeting and, discussions were ongoing as the same was an agenda item in the
upcoming Board meeting.
Onyeibo Oku asked [5] if there was an existing print-ready, A5 sized booklet
covering the basics of Fedora for handing out at events. Zoltan Hopper
responded [6] about a scratch document available at the Marketing Page. There
was further discussion around the difference between a Quick-Start and a
Handbook [7] and the possibility of building a Quick Start Guide [8] based upon
the SXSW Materials [9]
Christoph Wickert posted [10] Minutes of EMEA Ambassadors Meeting [11] The
thread [12] had additional discussion around allocation of funds under budget
line items and, expense planning based on projected needs. The decision making
process within FAmSCo was also discussed.
David Ramsey posted [13] meeting notes [14] from the APAC Ambassadors meeting
on 2011-03-19
David Ramsey informed [15] about an upcoming Power Management Test Day [16] and
subsequently posted [17] about the Printing and ABRT Retrace Server Test Days
Máirín Duffy asked [18] if there was a group photograph from a recent event
with the aim of updating the FUDCon Zurich group phot that is on
fedoraproject.org page
Christoph Wickert posted [19] a 'Last Call for Orders" for F14 media for any
event at EMEA and added a link to the Inventory [20] for helping to search for
the nearest anchor point
Pierros Papadeas posted [21] Meeting Minutes for FAmSCo meeting of 2011-03-26
Buddhika Kurera requested help [22] in finding a co-speaker for CLT2011
Paul Mellors posted [23] about an idea for a documentary [24] similar to
"Revolution OS"
Adam Miller put out a last call for funding for Texas Linux Fest 2011 [25]
1. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017242.html
2. ↑ https://fedoraproject.org/wiki/FAmSCo_report_2011-02
3. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017245.html
4. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017317.html
5. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017252.html
6. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017253.html
7. ↑ http://fedoraproject.org/wiki/User:Sankarshan/FedoraHandbook
8. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017261.html
9. ↑ https://fedoraproject.org/wiki/Design/SXSW_Materials
10. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017264.html
11. ↑
http://meetbot.fedoraproject.org/fedora-meeting/2011-03-23/emea_ambassadors.2011-03-23-20.02.html
12. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/thread.html#17264
13. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017265.html
14. ↑
http://meetbot.fedoraproject.org/fedora-meeting/2011-03-19/apac.2011-03-19-04.09.html
15. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017267.html
16. ↑ https://fedoraproject.org/wiki/Test_Day:2011-03-24
17. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017312.html
18. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017282.html
19. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017293.html
20. ↑ https://fedorahosted.org/emea-swag-tracking/wiki/Inventory
21. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017296.html
22. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017299.html
23. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017314.html
24. ↑ https://fedoraproject.org/wiki/Fedora_Documentary
25. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017310.html
--- Summary of events reported on Ambassadors mailing list ---
Christoph Wickert reported [1] on the Chemnitzer Linuxtage event with more
details about undertaking similar tasks using different distributions.
Fabian Affolter summarized [2] all the CLT2011 reports
1. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017241.html
2. ↑
http://lists.fedoraproject.org/pipermail/ambassadors/2011-March/017284.html
--- Summary of traffic on FAmSCo mailing list ---
Pierros Papadeas posted [1] the Agenda for the FAmSCo meeting of 2011-03-26 [2]
Joerg Simon, as the Fedora Ambassador Membership Administrator, informed FAmSCo
[3] about existing continuous violations of Fedora Ambassador Conduct [4]
Follow-up discussions happened on the ticket and the thread [5]
1. ↑ http://lists.fedoraproject.org/pipermail/famsco/2011-March/000736.html
2. ↑ https://fedoraproject.org/wiki/FAmSCo_agenda#2011-3-26_agenda
3. ↑ http://lists.fedoraproject.org/pipermail/famsco/2011-March/000737.html
4. ↑ https://fedorahosted.org/famsco/ticket/156
5. ↑
http://lists.fedoraproject.org/pipermail/famsco/2011-March/thread.html#737
-- QualityAssurance
In this section, we cover the activities of the QA team[1]. For more
information on the work of the QA team and how you can get involved, see the
Joining page[2].
Contributing Writer: Adam Williamson
1. ↑ http://fedoraproject.org/wiki/QA
2. ↑ http://fedoraproject.org/wiki/QA/Join
--- Test Days ---
Thursday 2011-03-24 was power management Test Day[1]. The event produced a
great turnout of testers who provided results on a wide range of hardware, and
the developers are already looking at the bugs filed. Thanks to everyone who
came out to help.
This Tuesday, 2011-03-29, was printing Test Day[2]. The turnout was a little
smaller than we hoped, but the testers who did come managed to find lots of
bugs, and Fedora's printing maintainer, Tim Waugh, was very happy with all the
results.
This Thursday, 2011-03-31, will be ABRT Test Day[3]. As well as checking that
ABRT (Fedora's automated crash report tool) is working as expected for Fedora
15, we'll be testing out a big new feature, the retrace server[4]. This allows
you to submit crash reports to a remote server which will generate the
backtrace - avoiding the need for you to download and install often large
debuginfo packages in order to submit reports. Please come along and help us
test this exciting new feature!
There is currently no Test Day planned for next Thursday, 2011-04-07. Take the
day off!
1. ↑ http://fedoraproject.org/wiki/Test_Day:2011-03-24
2. ↑ http://fedoraproject.org/wiki/Test_Day:2011-03-29
3. ↑ http://fedoraproject.org/wiki/Test_Day:2011-03-31_ABRT_Retrace_Server
4. ↑ http://fedoraproject.org/wiki/Features/RetraceServer
--- Anaconda testing ---
James Laska requested testing of an installer image which included updated
versions of anaconda and lorax that needed testing before being approved as
stable updates[1]. Several testers responded, and the updates were soon
approved.
1. ↑ http://lists.fedoraproject.org/pipermail/test/2011-March/098018.html
--- GNOME Tweak Tool testing ---
Michel Salim announced that GNOME Tweak Tool, an application for tweaking
various advanced settings in GNOME 3, was now available for testing[1]. Several
group members thanked Michel for the announcement and provided feedback on the
tool.
1. ↑ http://lists.fedoraproject.org/pipermail/test/2011-March/098107.html
--- Fedora 15 Beta preparation ---
The third Beta blocker/nice-to-have review meeting took place on 2011-03-25[1],
and the team worked through the full list of proposed Beta blocker and
nice-to-have bugs. The first test compose was scheduled for Tuesday 2011-03-22,
but could not be completed on that day due to various outstanding bugs and the
lack of the planned NetworkManager 0.9 packages. At a special release schedule
meeting on Wednesday 2011-03-23[2], the QA and release engineering teams, and
the Fedora Project Leader, agreed that the late arrival of NetworkManager 0.9
justified a one week slip in the release schedule. The first test compose was
then set for Tuesday 2011-03-29.
1. ↑
http://meetbot.fedoraproject.org/fedora-bugzappers/2011-03-25/f-15-beta-blocker.2011-03-25-16.59.html
2. ↑
http://meetbot.fedoraproject.org/fedora-meeting/2011-03-23/fedora-meeting.2011-03-23-19.30.html
--- Improving pre-release download page ---
Tim Flink passed on some feedback[1] he had received from a new tester who had
downloaded a pre-release and asked some questions in the #fedora IRC channel,
which does not handle pre-release issues. He suggested that it would be a good
idea to add some text to the pre-release download page[2] explaining the right
places to go to post feedback and get help with pre-release issues. Jóhann
Guemundsson and Adam Williamson both suggested filing a request with the
websites team, and Tim reported[3] that he had filed a ticket[4].
1. ↑ http://lists.fedoraproject.org/pipermail/test/2011-March/098160.html
2. ↑ http://fedoraproject.org/get-prerelease
3. ↑ http://lists.fedoraproject.org/pipermail/test/2011-March/098173.html
4. ↑ http://fedorahosted.org/fedora-websites/ticket/45
-- Security Advisories --
In this section, we cover Security Advisories from fedora-package-announce from
the past week.
http://lists.fedoraproject.org/pipermail/package-announce
Contributing Writer: Pascal Calarco
--- Fedora 15 Security Advisories ---
* libxml2-2.7.8-6.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/057031.html
* logrotate-3.7.9-8.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056992.html
* asterisk-1.8.3.2-1.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056945.html
* php-doctrine-Doctrine-1.2.4-1.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056936.html
* roundcubemail-0.5.1-1.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056917.html
* nss-3.12.9-14.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056832.html
* subversion-1.6.16-1.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056736.html
* libcgroup-0.37.1-1.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056734.html
* phpMyAdmin-3.3.10-1.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056730.html
* maniadrive-1.2-29.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056642.html
* php-eaccelerator-0.9.6.1-6.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056641.html
* php-5.3.6-1.fc15 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056640.html
--- Fedora 14 Security Advisories ---
* phpMyAdmin-3.3.10-1.fc14 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/057005.html
* wordpress-3.1-1.fc14 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/057003.html
* gnash-0.8.9-1.fc14 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056780.html
* libcgroup-0.36.2-6.fc14 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056683.html
* krb5-1.8.2-9.fc14 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056579.html
--- Fedora 13 Security Advisories ---
* phpMyAdmin-3.3.10-1.fc13 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/057007.html
* wordpress-3.1-1.fc13 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056998.html
* gnash-0.8.9-1.fc13 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056787.html
* krb5-1.7.1-18.fc13 -
http://lists.fedoraproject.org/pipermail/package-announce/2011-March/056573.html
-- LATAM Fedora! --
LATAM Fedora is a regular column of Spanish language contributions around open
source software. It is our first expansion into incorporating foreign language
content into FWN.
This week's contribution is from Guillermo Gómez, a second installment primer
on Ruby. Enjoy!
---- Ruby Capítulo 2 : Una clase algo más completa ----
Siguiendo nuestra secuencia al estilo tutorial, en esta edición vamos a
completar un poco más nuestras clases, introduciresmo los conceptos de métodos
y variables de clase.
Una variable de clase es una variable compartida de la clase misma. Sólo existe
una copia de una variable de clase en particular para una clase dada. Los
nombres de las variables de clase comienzan con @@ tal como en @@reproducciones.
1 class Cancion
2 @@reproducciones = 0
3
4 def Cancion.reproducciones
5 @@reproducciones
6 end
7
8 def reproducir
9 @@reproducciones =+ 1
10 end
11 end
A diferencia de las variables de instancia y variables globales, las variables
de clase deben se inicializadas antes de poder ser utilizadas, usualmente se
hace con una declaración simple en el cuerpo de la definición de la clase. En
el código anterior igualmente se ha introducido el concepto de método de clase.
Un método de clase es un método que no necesita que se instancie la clase para
ser invocado, es decir, "son métodos propios de la clase y no de sus objetos".
Su utilidad es obvia en el ejemplo, se quiere saber cuántas reproducciones se
han hecho en total en nuestro reproductor de música. Esta información no es
específica a una canción en particular, es decir, no es sujeto de las
instancias sino de la clase misma. La diferencia al momento de declarar el
método de clase es que debe anteponer el nombre de la clase al método, tiene
dos opciones, o usar explícitamente Cancion, o self. El uso de *self" da mayor
flexibilidad ya que permite cambiar el nombre de la clase sin mayores traumas.
1 class Cancion
2 @@reproducciones = 0
3
4 def self.reproducciones
5 @@reproducciones
6 end
7
8 def reproducir
9 @@reproducciones =+ 1
10 end
11 end
---- Constantes vs variables ----
Las variables y constantes en Ruby mantienen referencias a objetos. Las
variables no poseen un tipo intrínseco, a cambio el tipo es únicamente definido
por los mensajes a los que responde el objeto referenciado.
Una constante en Ruby también es una referencia a un objeto. Las constantes son
creadas cuando son asignadas por primera vez, a diferencia de otros lenguajes
Ruby le permite alterar el valor de las constantes si bien ello provocará un
mensaje de alerta. En general usted no debe alterar una constante en tiempo de
ejecución y debería evitarlo a toda costa.
1 >> MI_CONSTANTE = 1
2 => 1
3 >> MI_CONSTANTE = 2
4 (irb):23: warning: already initialized constant MI_CONSTANTE
5 => 2
Note como las constantes pueden declararse dentro de la definición de clase lo
que nos lleva a la definición de constante de clase y a la noción de espacios
de nombres por la forma en que nos referimos a dichas constantes.
1 class Cancion
2 VERSION="1.0"
3 end
1 >> Cancion::VERSION
2 => "1.0"
3 >> VERSION
4 => "1.8.7"
Note que VERSION no referencia ni colisiona con Cancion::VERSION.
---- El poder de herencia ----
Tal vez el santo grial de la programación es el principio DRY, "Don Repeat
Yourself". Una forma de evitar repetirse, es escribir código reusable, cada vez
que estamos escribiendo nuevo código y tenemos esa sensación de deja-vu de que
ya esto lo hicimos una vez en el pasado, es porque no estamos reusando nuestro
código de forma inteligente. En POO la herencia es una excelente forma de
mantener el código reusable sin mayores repeticiones.
La herencia le permite crear clases que sean refinamientos o especializaciones
de otra clase. Por ejemplo, y siguiendo el ejemplo de Cancion en nuestro
reproductor de música ahora a alguien se le ocurrió que sería interesante que
se incluyera el soporte para canciones de tipo Karaoke. La única diferencia con
las otras canciones es que las canciones Karaoke tienen asociadas la letra de
la canción en conjunto con infomación de sincronización para reproducir las
letras del Karaoke en nuestro flamante reproductor ahora con una gran pantalla
de video.
1 class Karaoke < Cancion
2 def initialize(nombre, artista, duracion, letra)
3 super(nombre, artista, duracion)
4 @letra = letra
5 end
6 end
El "< Cancion" en la definición de la clase le indica a Ruby que Karaoke es un
subclase de Cancion, o en dirección opuesta, Cancion es la superclase de
Karaoke. De esta forma la clase hija hereda todos los métodos y declaraciones
de variables de su padre. Al invocar un método sobre un objeto o clase, Ruby
defiere su ubicación hasta el momento de ejecución, en dicho momento Ruby
primero mira en la clase para determinar si existe el método invocado, si no es
así, intenta en el padre, y así atravesando todos los ancestros de la clase
hasta ubicar el método invocado. Si se acaban los ancestros donde buscar, Ruby
ejecuta una acción especial que puede ser interceptada si se desea
Object#method_missing, si no, produce un error.
Cada clase especializada maneja sus detalles, para el resto se utiliza super,
es decir, el método del padre o de su ancestro. De esta forma, por ejemplo, en
nuestra definición de Karaoke#initialize dejamos que la inicialización de todo
lo común a Cancion ocurra igual que antes por medio de la llamada a super con
los respectivos parámetros necesarios, luego inicializamos los datos
específicos a nuetras clase Karaoke.
---- Espacios de nombres ----
En la medida que escriba programas Ruby cada vez más grandes, usted
naturalmente se encontrará con código reusable, librerías de rutinas
relacionadas entre sí por ejemplo. Usted deseará separar dicho código en
distintos archivos separados de tal forma que el contenido pueda ser reusado
entre diferentes programas Ruby. Frecuentemente este código será organizado en
clases.
Otras veces ello simplemente no es conveniente o no aplica, son un grupo de
métodos que desea reusar, usted puede simplemente colocarlos en un archivo y
cargar dicho archivo en su programa con load o require. Esto funciona pero
tiene un problema, digamos que se crea una librería para cocinar con los
métodos calentar , mezclar, amasar en un archivo cocina.rb y otra librería para
atletas con los métodos calentar, correr, descansar en el archivo atleta.rb. Si
carga ambos archivos uno después del otro, simplemente el método calentar
colisiona y sólo el más recientemente cargado tendrá la definicón actual del
método, el otro simplemente será olvidado, en resumen la colisión en los
nombres es el problema.
La respuesta es el mecanismo de modulos. Los modulos definen un espacio de
nombres en donde sus métodos y constantes pueden aplicar sin tener que
preocuparse en colisionar con otros métodos y constantes:
1 module Cocina
2 ESCUELA="Latinoamericana"
3 def Cocina.calentar(x)
4 # Se espera que x sea un valor númerico para representar temperatura en oC
5 # ..
6 end
7 ...
8 end
9
10 module Atleta
11 ESCUELA="Simón Bolívar"
12 def Atleta.calentar(t)
13 # Se espera que t sea un valor numérico que represente tiempo en segundos
14 # ..
15 end
16 end
1 >> Cocina::ESCUELA
2 => "Latinoamericana"
3 >> Atleta::ESCUELA
4 => "Simon Bolivar"
5 >> include Atleta
6 => Object
7 >> Atleta.calentar(1000)
8 calentando 1000 segundos
9 => nil
10 >> include Cocina
11 => Object
12 >> Cocina.calentar(10)
13 => 10
Ahora entonces tiene mucho menos probabilidades de provocar colisiones, note
que debe cargar el código, y luego include para usar las funcionalidades del
módulo.
---- Herencia múltiples vs Mixins ----
Algunos lenguajes orientados a objetos, tales como C++, soportan herencia
múltiple en donde una clase puede tener más de una superclase heredando
funcionalidad de cada una de ellas. Si bien potente, esta técnica puede ser
peligrosa ya que la jerarquía puede tener ambigüedades. Otros lenguajes como
java y C# soportan sólo herencia simple. Si bien más limpia y simple, la
herencia simple también tiene sus desventajas, en la realidad los objetos
heredan atributos de múltiples fuentes en el mundo real.
Ruby ofrece una alternativa interesante y poderosa que le ofrece la simplicidad
de la herencia simple y el poder la herencia múltiple. Una clase Ruby tiene una
única clase padre, en consecuencia Ruby es un lenguaje con herencia simple, sin
embargo, las clases Ruby pueden incluir la funcionalidad de cualquier cantidad
de mixins (un mixin es una especie de definición parcial de clase). Nuevamente
dejemos que Ruby hable, creemos nuestro archivo con la definición de módulo y
un par de clases tontas que lo usen como mixin:
---- mixin_module.rb ----
1 module Debug
2 def quien_soy?
3 "#{self.class.name} (\##{self.objet_id}): #{self.to_s}"
4 end
5 end
6
7 class Cocina
8 include Debug
9 def estilo
10 puts "Italiana"
11 end
12 end
13
14 class Nevera
15 include Debug
16 def capacidad
17 puts "150 pies cúbicos"
18 end
19 end
Si ahora cargamos dichas definiciones de módulo y clases en irb, podemos
evidenciar y experimentar con el uso de los mixins (note que le voy a pasar la
forma de hacerlo):
1 $ irb
2 >> load 'mixin_module.rb'
3 => true
4 >> nevera = Nevera.new
5 => #<Nevera:0xb7587b38>
6 >> cocina = Cocina.new
7 => #<Cocina:0xb7585c5c>
8 >> nevera.quien_soy?
9 => "Nevera (#-609469028): #<Nevera:0xb7587b38>"
10 >> cocina.quien_soy?
11 => "Cocina (#-609472978): #<Cocina:0xb7585c5c>"
Bien, es todo por hoy, nos recontraremos en un tercer capítulo dedicado a
métodos en una próxima edición de esta serie dedicada a aprender Ruby.
Este artículo se mantiene en línea en gomix.fedora-ve.org para posibles mejoras
y erratas.
Guillermo Gómez
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