FWN/Issue265

Fedora Weekly News Issue 265

Welcome to Fedora Weekly News Issue 265 for the week ending March 2, 2011. What follows are some highlights from this issue.

Our issue kicks off with a couple outage announcements from this past week, followed by three articles 'In the News', including an interview with Fedora Program Manager, Robyn Bergeron. In Ambassador news, summaries of traffic on the Ambassador and FAmSCo lists, and QA brings us a whole slew of Test Day details over the next few weeks, Fedora 15 prep and bodhi improvements. Security Advisories keeps us updated with security-related patches released this past week. We're also very pleased this week to kick off our foreign language content initiative, which developed out of FUDCon Tempe, with a new Latin American beat, all in Spanish. To start off, we have part one of a Ruby on Fedora primer, contributed by Guillermo Gómez, a Fedora Ambassador in Venezuela. If you would like to contribute Fedora-related content in your language, please send a note to the editors!

An audio version of some issues of FWN - FAWN - are available! You can listen to existing issues 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. We welcome reader feedback: news@lists.fedoraproject.org

FWN Editorial Team: Pascal Calarco, Adam Williamson

Announcements

In this section, we cover announcements from the Fedora Project, including general announcements, development announcements and Events.

Contributing Writer: Rashadul Islam

Fedora Announcement News

The announcement list is always exclusive for the Fedora Community. Please, visit the past announcements at

Infrastructure Outage Notification: 2011-03-02 1200 UTC -> 1500 UTC

Stephen John Smoogen on Tue Mar 1 20:13:07 UTC 2011 announced,

"Tomorrow the services at ibiblio will be moved to a new physical location

• ibiblio01.fedoraproject.org
• app05
• backup02
• ns02
• proxy04
• smtp-mm03
• torrent01"

Updated: Outage: Ibiblio/ipv6 servers - 2011-03-02 14:00 UTC

Stephen John Smoogen on Tue Mar 1 22:09:31 UTC 2011 announced,

"Outage: Ibiblio/ipv6 servers - 2011-03-02 14:00 UTC

There will be an outage starting at UTC, 2011-03-02 14:00 which will last approximately 4 hours.

To convert UTC to your local time, take a look at or run:

date -d '2011-03-02 14:00 UTC'

Reason for outage

metalabs is moving facilities and needs for our collocated server to move with them. Systems will be down and getting new IP addresses with the move.

Contact Information

Please join #fedora-admin in irc.freenode.net or respond to this email to track the status of this outage."

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 (Dec 2010 - Feb 2011)

• North America (NA)
• Central & South America (LATAM):
• Europe, Middle East, and Africa (EMEA)
• India, Asia, Australia (India/APJ)

Past Events

Archive of Past Fedora Events

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.

http://fedoraproject.org/wiki/Marketing

Contributing Writer: Pascal Calarco

Who Contributes the Most to LibreOffice? (Linux Journal)

Rahul Sundaram forwarded an article from Linux Journal noting contributions to LibreOffice:

"Bosdonnat began tracking line contributions in the middle of September 2010 with the original 14 contributions being made by Oracle. Oracle actually contributes code to OpenOffice.org, and then LibreOffice merges those changes, thus resulting in Oracle's contributions to the new fork. These 112 contributions have continued throughout development, but are dwarfed by the contributions of new developers."

These contributions make up well over half of the total new changes found in LibreOffice as of mid-February. Weekly contributions in this area have averaged between 20 and 30 with a total number of 517 line contributions.

Red Hat, who also contributed to OpenOffice.org, has chipped in as well. With usually two contributions per week, Red Hat developers have provided 39 patches since the fork."

The full article is available.

Fedora 15 alpha delayed - Btrfs may be default in 16 (H Online)

Rahul Sundaram forwarded an an article in The H Online about the decision to push back Fedora 15 alpha:

"The Fedora project has postponed the release of the first and only alpha version of Fedora 15, originally scheduled for 1 March, by a week. This was due, at least in part, to a bug in X Server that occurred in connection with keyboard layouts for such languages as German or French and prevented users from successfully logging into GDM. Subsequent milestones in the release schedule for Fedora 15 remain unaffected at present, and the final release is still scheduled for 10 May.

The fifteenth Fedora release is currently planned to be the first version that won't require a special boot parameter to be submitted to the installer in order to format a storage device with the experimental Btrfs file system. Red Hat employee Josef Bacik, who is heavily involved in the development of Btrfs, has now proposed on the project's most important developer mailing list that Btrfs should be made the default file system in Fedora 16, which is expected in late October or early November"

The full post is available.

Beyond FUDCon with Robyn Bergeron, Fedora Program Manager (Linux Magazine)

Rahul Sundaram forwarded another article highlighting Fedora community leaders, this with Robyn Bergeron, who remarked:

"I personally would love to see more folks getting involved in areas that don't necessarily require coding skills. I think that there is enormous room for growth and contribution in these areas, and there are plenty of Linux enthusiasts out there who have the skills and imagination to make great contributions in these places."

The full article is available

Ambassadors

This section covers the news surrounding the Fedora Ambassadors Project.

Contributing Writer: Sankarshan Mukhopadhyay

Welcome New Ambassadors

This week the Fedora Ambassadors Project had no new members joining.

Summary of traffic on Ambassadors mailing list

Pierros Papadeas posted about Ambassador SOPs on which FAmSCo has been working.

Clint Savage suggested attending the FAD at SCaLE this year specifically mentioning the Sysadmin Study Group

Buddhika Kurera informed that the order for the FAm T-shirts had been placed and expected delivery is around end of March (impacted by the orders around the ICC Cricket World Cup)

Neville A. Cross asked if any other Fedora Project participants would be attending PyCon from 2011-03-08 till 2011-03-13. Mark McIntyre responded and provided his plans. Max Spevack suggested creating an Event page and also posting to devel at lists.fedoraproject.org. The page was created by Mark McIntyre

Pierre-Yves Chibon posted the translated annual report for Fedora-Fr, the French speaking NPO.

David Ramsey provided prior notice about Fedora 15 Test Days coming up

David Ramsey posted the draft Agenda of the APAC meeting on 2011-03-05

Caius Chance informed about having around 700 F14 LiveCDs with him at Brisbane and wanted to get them to Fedora Ambassadors in APAC soonest. The thread had requests from Ambassadors who wanted the CDs.

Christoph Wickert announced that the Trac instance used by the Fedora Board was open for ticket submissions by all FAS account holders.

Christoph Wickert provided an update on the Fedora 14 media for EMEA

Max Spevack posted an initial announcement of the Finance SIG

David Ramsey posted about Summer Coding Ideas for 2011

Larry Cafiero posted Meeting Minutes from FAmNA meeting on 2011-03-01

Summary of events reported on Ambassadors mailing list

No event reports were posted to the Ambassadors mailing list.

Summary of traffic on FAmSCo mailing list

Caius Chance informed about having around 700 F14 LiveCDs with him at Brisbane and wanted to get them to Fedora Ambassadors in APAC soonest.

Max Spevack posted an initial announcement of the Finance SIG

QualityAssurance

In this section, we cover the activities of the QA team. For more information on the work of the QA team and how you can get involved, see the Joining page.

Contributing Writer: Adam Williamson

Test Days

Thursday 2011-02-17 was Xfce 4.8 Test Day. The event was well organized by the Xfce team, and a dedicated group of testers was able to expose some important bugs to be fixed.

The week of 2011-02-21 saw the traditional Graphics Test Week. Adam Williamson posted a full recap of the event to the mailing list. He noted that participation was up again compared to the Fedora 14 events and that some important testing had been carried out, but also noted a worrying trend in status of bugs from previous events, with many bugs reported during the Fedora 13 and 14 events remaining unfixed. He promised to investigate the causes of this.

This week (and next Tuesday!) is internationalization and localization Test Week, and Adam Williamson put up a blog post explaining the three Test Days this includes: the Anaconda i18n and l10n Test Day on 2011-03-01, the desktop i18n Test Day on 2011-03-03 and the desktop l10n Test Day on 2011-03-08. All these events are very important to ensure that non-US-English-speaking users of Fedora get a great experience with Fedora 15.

Thursday 2011-03-10 will be the second of three planned GNOME 3 Test Days, where we'll continue to work with the GNOME team to test GNOME 3.0 and its integration with Fedora 15 as rigorously as we can before the final release of both. We'll be repeating the tests from the previous event to see how things have progressed, and also running some new tests which have been added for this event. As before, this is a very important event for both Fedora and GNOME and affects most Fedora users, so if you have a few minutes to spare, please come along and help testing. Once again, live images will be available to make it easier to test, and we'll have a new process in place for reporting crasher bugs without the trouble of trying to install debuginfo packages on a live image!

Fedora 15 Alpha preparation

The QA team has been busy over the last two weeks validating the Fedora 15 Alpha release, with TC2, RC1, and RC2 candidate builds being posted and tested. As always, the whole team chipped in with the all-important testing. In the end the RC1 image was not accepted and the release delayed for a week due to a significant bug with many non-English keyboard layouts which was exposed during the testing. With this bug fixed, the RC2 image was accepted as gold at the go/no-go meeting of 2011-03-02.

Bodhi improvements

At the weekly meeting of 2011-02-28, Luke Macken announced that package-specific test case integration into Bodhi is now live, meaning that packages which have test cases associated with them according to the package test plan SOP will now have the test cases displayed in Bodhi when an update for the package is under review. Also going live in the new Bodhi release are the improvements to the automated messages Bodhi sends to Bugzilla when an update's status changes, improvements discussed in previous issues of this newsletter.

FreeIPA Test Day problems and proposals

Dmitri Pal posted a comment to the FreeIPA Test Day trac ticket noting that he was unhappy with the way the event had turned out. Adam Williamson, James Laska and Jóhann Guðmundsson joined in with suggestions to try and learn from this experience. Dmitri is considering re-running the event with some tweaks.

Complications for Delta ISO users

Andre Robatino provided some detailed information on what a change to the xz compression scheme would mean for users of DeltaISOs. In a nutshell, users trying to use Fedora 14 -> Fedora 15 DeltaISOs will need to use a workaround, detailed in the post, if applying the ISO on a Fedora 14 system. Andre followed up later with a refinement of the workaround.

IPv6 testing

A.J. Werkman provided a recap of some very solid testing he had performed on Fedora's out-of-the-box IPv6 capabilities. He identified some significant problems and reported them as bugs, including anaconda refusing to work without an IPv4 DHCP lease, and Fedora's Bugzilla not being available in the IPv6 domain.

Using abrt during Test Days

A thread started by Mike Cloaked highlighted the issue of abrt being difficult or impossible to use successfully from live images (such as during Test Days), in large part due to the size of debuginfo packages. Adam Williamson pointed out that the abrt team's retrace server project would be a perfect solution for this, but noted that he had not yet tested using it. When he did, it seemed not yet to be ready for Fedora 15. Jiri Moskovc said that the Fedora 15 support would soon be available.

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 14 Security Advisories

none

Fedora 13 Security Advisories

• ruby-1.8.6.420-2.fc13 - http://lists.fedoraproject.org/pipermail/package-announce/2011-March/054436.html
• abcm2ps-5.9.21-1.fc13 - http://lists.fedoraproject.org/pipermail/package-announce/2011-March/054424.html
• telepathy-glib-0.11.16-2.fc13 - http://lists.fedoraproject.org/pipermail/package-announce/2011-March/054409.html
• telepathy-gabble-0.10.5-1.fc13 - http://lists.fedoraproject.org/pipermail/package-announce/2011-March/054408.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 primer on Ruby. Enjoy!

Ruby Capítulo 1: El primer contacto

"Yo quería un lenguaje de programación más poderoso que Perl y más orientado a objetos que Python. Entonces me acordé de mi viejo sueño y decidí diseñar mi propio lenguaje. Al principio estuve jugando con él en el trabajo. Gradualmente creció lo suficiente como para remplazar a Perl. Lo llamé Ruby en honor a esa piedra preciosa roja y lo liberé al público en 1995."

Yukihiro Matsumoto, a.k.a. Matz Japan, October 2000

Aprovechando el espacio

Para comenzar en Fedora con Ruby vamos instalar lo mínimo necesario y sin perder mucho espacio dando vueltas con teoría y opiniones, directo al grano. Abra una sesión de emulación de terminal preferida y siga las siguientes instrucciones para instalar. En la medida que desarrollemos esta columna dedicada a Ruby, entonces iremos descubriendo el poder y flexibilidad de Ruby.

 $ su -
 <contraseña de root>
 # yum install ruby ruby-rdoc ruby-ri

Para el editor, hay muchas opciones, mi editor de preferencia es Vim , pero puede usar el de su preferencia, intente usar alguno que pueda resaltar sintaxis Ruby como mínimo. Puede escoger desde entornos tan complejos y completos como Eclipse, hasta editores de escritorio GUI como Gedit, o simples en consola como nano o complejos y sofisticados como Vim y Emacs.

Los "Hola mundo"

La primera forma interactiva simple de ejecutar comandos Ruby es simplemente usar el intérprete, simplemente ejecute el intérprete, ingrese los comandos y termine presionando Ctrl-D para indicarle al intérprete que la entrada de comandos ha finalizado:

 $ ruby
 puts "Hola Mundo" 
 <Ctrl-D>
 Hola Mundo

La segunda forma interactiva es con irb. irb es el acrónimo para Interactive Ruby. irb es un shell Ruby, es decir, es un espacio donde puede evaluar su código al instante. En próximas ediciones iremos desarrollando más el tema de irb, por ahora simplemente invoque a irb e intente:

 $ irb
 irb(main):001:0> puts "Hola Mundo" 
 Hola Mundo
 => nil
 irb(main):002:0>exit 
 $

Si lo que quiere es crear un programa Ruby que nos imprima "Hola Mundo" en la salida del monitor, lance su editor e incluya el siguiente código fuente en un archivo denominado holamundo.rb., guarde y salga de su editor.

holamundo.rb

 1 puts "Hola Mundo" 

Para ejecutar simplemente pásale al intérprete Ruby el archivo como argumento.

 [gomix@fricky capitulo_1]$ ruby holamundo.rb 
 Hola Mundo

También puede usar el método "shebang" y convertir el archivo fuente Ruby en ejecutable del sistema, edite su holamundo.rb para que luzca como se muestra en el listado a continuación.

holamundo.rb

 1 #!/usr/bin/ruby 
 2 
 3 puts "Hola Mundo" 

 [gomix@fricky capitulo_1]$ chmod +x holamundo.rb
 [gomix@fricky capitulo_1]$ ./holamundo.rb 
 Hola Mundo

Existe la forma de pasarle directamente código Ruby al intérprete sin apoyo de archivos o programas adicionales y sin entrar en modo interactivo.

 $ ruby -e 'puts "Hola Mundo"'
 Hola Mundo

Ruby es un lenguaje de programación orientado a objetos

Todo lo que usted manipula en Ruby es un objeto, y los resultados de dichas manipulaciones a su vez, también son objetos. Cuando usted escribe código orientado a objetos normalmente está modelando conceptos del mundo real en su código. Típicamente durante este proceso de modelado usted descubrirá categorías de cosas que necesitan ser representadas en código. En un reproductor de música el concepto de "canción" puede ser una de esas categorías. En Ruby usted define una clase para representar cada una de esas entidades. Una clase es una combinación de estado, por ejemplo el nombre de la canción, y métodos que usan dicho estado, por ejemplo para reproducir la canción.

Una vez que tiene dichas clases usted creará instancias de dicha clase. Para el reproductor de música que contiene la clase Cancion usted terminará teniendo instancias separadas independientes para canciones populares como "Todo o nada", "Canción para un amigo", "Amanecer llanero", y por el estilo. La palabra objeto e instancia son intercambiables. En Ruby para crear dichas instancias u objetos, se debe llamar a un método constructor de la clase, el método constructor estandar se llama new.

 1 cancion1 = Cancion.new("Amanecer llanero")
 2 cancion2 = Cancion.new("Todo o nada")

Estas instancias son derivadas de la misma clase pero tienen características únicas. Primero, cada objeto tiene un object_id único. Segundo, usted puede definir variables de instancia, variables con valor que son únicos para cada instancia. Estas variables de instancia mantienen el estado del objeto. Igualmente puede definir métodos de instancia para acceder y/o alterar el estado del objeto, es decir, acceder y/o alterar las variables de instancia. Rápidamente definamos nuestra clase Cancion. Ruby se puede leer fácilmente.

1 class Cancion
2   def titulo
3     @titulo
4   end
5 
6   def titulo=(titulo_de_la_cancion)
7     @titulo = titulo_de_la_cancion.to_s
8   end
9 end

Claramente podemos ver y leer que hemos definido la clase de nombre Cancion con dos métodos de instancia, titulo y titulo=. La variable de instancia se representa en @titulo , con la notación de nombre de variable en minúscula precedida del símbolo @ .

Note la indentación que hemos implementado para representar la estructura, dos espacios es cómun entre los Rubyeros (me gusta llamarlos así).

Es evidente que la plabra clave class establece el inicio de un bloque que se cierra con end para definir una clase con nombre, en este ejemplo Cancion. Dentro de dicha estructura también podemos identificar claramente la palabra clave def que igualmente define bloques que se cierran también con la palabra clave end. def define dos métodos de instancia en este ejemplo. Hablaremos más de def de forma recurrente en muchas ediciones de esta columna.

Podemos probar nuestra clase en irb fácilmente, por ahora tipee con cuidado para no equivocarse, luego le ofreceré más técnicas irb.

  1 $ irb
  2 >> class Cancion
  3 >> def titulo
  4 >> @titulo
  5 >> end
  6 >> def titulo=(titulo_de_la_cancion)
  7 >> @titulo = titulo_de_la_cancion.to_s
  8 >> end
  9 >> end
 10 => nil
 11 >> cancion1 = Cancion.new
 12 => #<Cancion:0xb76e25c8>
 13 >> cancion1.titulo="Alma llanera" 
 14 => "Alma llanera" 
 15 >> cancion1.titulo
 16 => "Alma llanera" 

Pero no necesito clases

También se puede usar Ruby del modo procedimental, funcional, sin necesidad de crear (explícitamente) clases y objetos.

 1 $ irb
 2 >> 2 + 2
 3 => 4

Pero igual note que estamos trabajando con objetos de alguna clase, en nuestro ejemplo Fixnum.

 1 >> 2.class
 2 => Fixnum

Puede definir métodos y llamarlos:

 1 >> def saludo
 2 >> puts "Hola Mundo" 
 3 >> end
 4 => nil
 5 >> saludo
 6 Hola Mundo
 7 => nil

Clases base

Ya que "todo" son objetos de alguna clase, más vale que comencemos por aprender las más fundamentales del lenguaje, Fixnum, Bignum, Float, String, Array y Hash.

Números... Fixnum, Bignum, Float

Enteros, dejemos que nuestro código Ruby hable.

  1 >> num = 8
  2 => 8
  3 >> 7.times do
  4 ?> print num.class, " ", num, "\n" 
  5 >> num *= num
  6 >> end
  7 Fixnum 8
  8 Fixnum 64
  9 Fixnum 4096
 10 Fixnum 16777216
 11 Bignum 281474976710656
 12 Bignum 79228162514264337593543950336
 13 Bignum 6277101735386680763835789423207666416102355444464034512896
 14 => 7
 15 >> num = 3.14
 16 => 3.14
 17 >> 8.times do
 18 ?> print num.class, " ", num, "\n" 
 19 >> num *= num
 20 >> end
 21 Float 3.14
 22 Float 9.8596
 23 Float 97.21171216
 24 Float 9450.11698107869
 25 Float 89304710.9560719
 26 Float 7.97533139894754e+15
 27 Float 6.36059109230385e+31
 28 Float 4.04571190434951e+63

Cadenas de caracteres, String

 1 >> "Hola Mundo".class
 2 => String
 3 >> "987".class
 4 => String
 <

Arreglos, Array

 1 >> arreglo = ["a",1,"b",2]
 2 => ["a", 1, "b", 2]
 3 >> arreglo.class
 4 => Array
 5 >> arreglo[0]
 6 => "a" 
 7 >> arreglo[1]
 8 => 1
 <

Arreglos indexados arbitrariamente, Hash

1 >> hash = { "color" => "rojo", "temperatura" => 75, 1 => "hoy"}
2 => {1=>"hoy", "temperatura"=>75, "color"=>"rojo"}
3 >> hash.class
4 => Hash
5 >> hash["color"]
6 => "rojo" 
7 >> hash["temperatura"]
8 => 75
9 >> hash[1]

10 => "hoy"

Recapitulación rápida, los objetos y sus métodos, ¿documentación?

Teniendo cualquier objeto de cualquier clase a la mano, para acceder a su métodos podemos usar la sintaxis objeto.método. En el ejemplo abajo llamamos al popular método to_s que nos ofrece una representación en String del objeto en cuestión.

 1 >> hash.to_s
 2 => "1hoytemperatura75colorrojo" 
 3 >> arreglo.to_s
 4 => "a1b2" 
 5 >> 8.to_s
 6 => "8" 

Ahora bien, ¿dónde consigo la documentación de dichas clases y métodos? Demos la bienvenida a ri para ayuda local en línea de comandos, y por supuesto, en la web a http://www.ruby-doc.org/ . Francamente, en nuestros días la primera fuente de información es la Web, y en segundo lugar, nuestros recursos locales como ri. Entonces, y para efectos de esta serie de artículos, vamos a usar inicialmente Ruby 1.8.7.

• http://www.ruby-doc.org/core-1.8.7/
• http://www.ruby-doc.org/stdlib-1.8.7/

Ejemplo de salida ri (extracto).

 $ ri Fixnum
 ------------------------------------------------ Class: Fixnum < Integer
    A +Fixnum+ holds +Integer+ values that can be represented in a
    native machine word (minus 1 bit). If any operation on a +Fixnum+
    exceeds this range, the value is automatically converted to a
    +Bignum+.
 ...
 Instance methods:
 -----------------
    %, &, *, **, +, -, -@, /, <, <<, <=, <=>, ==, >, >=, >>, [], ^,
    __serialize__, abs, dclone, div, divmod, html_safe?, id2name,
    modulo, power!, quo, rdiv, rpower, size, to_f, to_s, to_sym, xchr,
    zero?, |, ~

Ruby es dinámico ¿ 2 + 2 = 4 ?

Uno de los aspectos notables de Ruby es su dinamismo, una forma de visualizarlo es hacer uso del hecho que todas las clases están "abiertas" y es posible redefinir sus métodos, por ejemplo:

fixnum_mod.rb

 #!/usr/bin/ruby
 #
   class Fixnum
     def +(otro)
       100
     end
   end

 puts (2+2).to_s

Y ahora ejecutamos nuestro programa:

 $ ruby fixnum_mod.rb 
 100

Horror, hemos echado a perder el método sumar de Fixnum, por ello algunos consideran peligroso los lenguajes dinámicos, sin embargo existe la forma de protegernos de este tipo de modificaciones en el caso de que ello no sea deseable. El ejemplo sin embargo demuestra que toda clase puede redefinir cualquiera de sus métodos en tiempo de ejecución, en cualquier momento, este dinamismo le da gran poder a Ruby, piense en una clase u objeto que evoluciona y gana funcionalidad en el tiempo de existencia del programa, o que la pierde, su funcionalidad puede mutar, cambiar. No puede devolver el cambio, no sin que le enseñe cómo preservar el código sobrescrito, probablemente en la próxima edición de esta columna.

Estructuras de control

Por supuesto que ningún lenguaje está completo si no tiene la capacidad de ejecución de código condicionada, es decir, evaluar alguna condición o estado, y proceder en consecuencia de distintas maneras. Abajo le resumimos las estructuras más comunes.

 1 # Evaluacion máxima 20
 2 if evaluacion < 10
 3   puts "Usted reprobó la asignatura." 
 4 elsif evaluacion > 16
 5   puts "Usted obtuvo un grado sobresaliente." 
 6 else
 7   puts "Usted aprobó la materia." 
 8 end

 1 unless unaCancion.duracion > 180 then
 2   costo = .25
 3 else
 4   costo = .35
 5 end

 1 case forma
 2   when Cuadrado, Rectangulo
 3     # ...
 4   when Circulo
 5     # ...
 6   when Triangulo
 7     # ...
 8   else
 9     # ...
 10 end

Lazos e iteradores

Un iterador en Ruby es simplemente un método que puede invocar un bloque de código. Note como se pasa la referencia del bloque de código y este a su vez ejecutado por medio de la llamada yield.

Ruby	Salida
1 def tres_veces	Hola mundo
2 yield	Hola mundo
3 yield	Hola mundo
4 yield
5 end
6
7 tres_veces { puts "Hola Mundo" }

Algunos iteradores son muy comunes en muchas clases Ruby para representar colecciones, por ejemplo each en un arreglo simple. Note que each además de iterar por cada uno de los elementos del arreglo, pasa un argumento al bloque de código ha ser ejecutado, en este caso pasa el contenido correspondiente en el arreglo.

Ruby	Salida
i| puts i }	1
	3
	5
	7
	9

Lazos con while y until.

Ruby	Salida
1 peso = 5	10
2 while peso < 100	20
3 peso = peso * 2	40
4 puts peso	80
5 end	160

Ruby	Salida
1 peso = 5	10
2 until peso > 100	20
3 peso = peso * 2	40
4 puts peso	80
5 end	160

Lazo con for y loop:

Ruby	Salida
1 for i in 1..8 do	1
2 puts i	2
3 end	3
	4
	5
	6
	7
	8

Ruby	Salida
1 num = 0	En el lazo por 0 vez
2 loop do	En el lazo por 2 vez
3 puts "En el lazo por #{num} vez"	En el lazo por 2 vez
4 num += 1	En el lazo por 3 vez
5 break unless num < 5	En el lazo por 4 vez
6 end

De salida, por supuesto hay mucho más acerca de Ruby y su mundo, usted podrá hacer desde pequeños guiones (scripts) hasta poderosas aplicaciones de escritorio o su último desarrollo web, no se detenga aquí y espero que nos leamos en la próxima entrega de esta publicación, envíeme sus comentarios a <gomix@fedoraproject.org>.

Nuestro trabajo es resolver problemas concretos, no alimentar al compilador con cucharilla, nos gustan los lenguajes dinámicos que se adapten a nosotros sin reglas rígidas que seguir.

Gomix_