Good Ruby Examples?

hcatlin · December 1, 2005, 3:20pm

I’m planning on doing a tutorial about Ruby for Ryerson University’s CS
Majors group. No one here knows anything about Ruby, so I thought it’d
be a great way to evangelize a bit. I’m always surprised how few
students actually code at all on their own. Most of them know Java and
C from class, but find them to be nothing more than class projects.

What I’m asking you guys for is if you have any short code ideas that
can be programmed really quickly in Ruby that might illustrate its
versatility. Some code example that would be hell to write in other
languages that would be interesting for an hour long explaination. I’d
say about 20 to 30 lines or so.

So, what’s everybody’s favorite smallish examples of the power of
coding with Ruby.

-hampton.

hcatlin · December 1, 2005, 4:17pm

C has ‘Hello world!’
Ruby has the proverbial ‘ToDo’ list,
Peak Obsession

hcatlin · December 1, 2005, 5:02pm

Lou V. wrote:

C has ‘Hello world!’
Ruby has the proverbial ‘ToDo’ list,
Peak Obsession

Except the typical C “Hello, world” example doesn’t start with, “First,
download and install a set of libraries that does all the interesting
bits.”

For a small example, show the use of blocks. Give a Rake demo, then
examine the Rake lib code that mkaes it possible.

Maybe go through the code of Jim W.'s Builder library, or something
else that shows the power of method_missing and dynamic code invocation.

James

–

http://www.ruby-doc.org - Ruby Help & Documentation
Ruby Code & Style - Ruby Code & Style: Writers wanted
http://www.rubystuff.com - The Ruby Store for Ruby Stuff
http://www.jamesbritt.com - Playing with Better Toys
http://www.30secondrule.com - Building Better Tools

hcatlin · December 1, 2005, 6:02pm

On Dec 1, 2005, at 9:57 AM, James B. wrote:

Lou V. wrote:

C has ‘Hello world!’
Ruby has the proverbial ‘ToDo’ list,
Peak Obsession

Except the typical C “Hello, world” example doesn’t start with,
“First, download and install a set of libraries that does all the
interesting bits.”

I agree. Avoid introducing 50 great add-on tools and target language
basics.

For a small example, show the use of blocks.

Amen.

I was reading a Java book this morning that talked about the Visitor
Design Pattern (pretty block-like) as the root of all evil in the
world. I actually got mad reading the text. Now I realize, they
just don’t “get it”…

Give a Rake demo…

Wait, didn’t we just get back to downloading libraries? (I’m
kidding around here. It’s a fine idea.)

Perhaps there’s a decent topic, or just some inspiration, hiding in
the Ruby Q.zes (http://rubyquiz.com/). Of course, we know I’m
biases there.

James Edward G. II

hcatlin · December 1, 2005, 6:11pm

I was reading a Java book this morning that talked about the Visitor
Design Pattern (pretty block-like) as the root of all evil in the
world. I actually got mad reading the text. Now I realize, they
just don’t “get it”…

Java, not supporting double-dispatch, can turn a pretty pattern like
Visitor into a mess.

hcatlin · December 1, 2005, 5:19pm

If you want to show them how fun ruby is: start with a c/java program
and translate it to ruby step-by-step.
Like this one:
http://onestepback.org/articles/groovy/ajavaprogram.html

Maybe something like:

a = false
puts (‘aa’…‘zz’).select{a = !a}

prints:
aa
ac
ae
etc.

Will be huge in java

This can be an introduction, but you need a practical example too.

hcatlin · December 1, 2005, 6:19pm

James B. wrote:

Lou V. wrote:

C has ‘Hello world!’
Ruby has the proverbial ‘ToDo’ list,
Peak Obsession

Except the typical C “Hello, world” example doesn’t start with, “First,
download and install a set of libraries that does all the interesting
bits.”

Good point. You get to show what a rich set of libraries Ruby has and
how easy libraries can be installed with just one command. Thanks for
pointing that out.

-lv

[snip]

hcatlin · December 1, 2005, 6:35pm

James Edward G. II wrote:

On Dec 1, 2005, at 9:57 AM, James B. wrote:

Give a Rake demo…

Wait, didn’t we just get back to downloading libraries? (I’m
kidding around here. It’s a fine idea.)

The idea is to give a Rake demo, and then examine the Rake library code
itself as the real example of Ruby. No hand waving (which a Rake demo
alone would entail); show how Ruby lends itself to robust, high-level
abstractions (such as Rake tasks).

James

http://www.ruby-doc.org - Ruby Help & Documentation
Ruby Code & Style - Ruby Code & Style: Writers wanted
http://www.rubystuff.com - The Ruby Store for Ruby Stuff
http://www.jamesbritt.com - Playing with Better Toys
http://www.30secondrule.com - Building Better Tools

hcatlin · December 1, 2005, 6:39pm

Lou V. wrote:

Except the typical C “Hello, world” example doesn’t start with,
“First, download and install a set of libraries that does all the
interesting bits.”

Good point. You get to show what a rich set of libraries Ruby has and
how easy libraries can be installed with just one command. Thanks for
pointing that out.

A valuable aspect of Ruby and gems, but it says nothing about the
language per se.

I’d be wary of emphasizing the “rich set of libraries” aspect, too, as
Python, Perl, and Java probably have Ruby beat.

Better to show how much one can do, and how easily, without extra
libraries.

Ruby’s biggest selling point is Ruby itself.

James

http://www.ruby-doc.org - Ruby Help & Documentation
Ruby Code & Style - Ruby Code & Style: Writers wanted
http://www.rubystuff.com - The Ruby Store for Ruby Stuff
http://www.jamesbritt.com - Playing with Better Toys
http://www.30secondrule.com - Building Better Tools

hcatlin · December 1, 2005, 9:46pm

I’m not sure what level your students are, but a demo of drivting
Internet Explorer with the Watir project code
(http://wtr.rubyforge.org) is colorful and fun. Advanced students can
investigate the Watir libraries and discuss Domain Specific Languages;
less advanced students can investigate the Watir unit tests and
examples quite easily. For instance, the code below is from the Watir
distribution and tests Google Maps:

require ‘watir’
include Watir
require ‘test/unit’

class TC_google_maps < Test::Unit::TestCase

def test_google_maps

    testSite = "http://maps.google.com"
    ie = IE.new
    ie.goto(testSite)
    ie.text_field(:id,"q").set("Durango,CO")
    ie.button(:index, 1).click

    matchlat = '37.275278'
    matchlong = '-107.879444'

        assert_match(matchlat,ie.frame("vp").html.to_s)
        assert_match(matchlong,ie.frame("vp").html.to_s)
end

end

hcatlin · December 1, 2005, 7:28pm

So, what’s everybody’s favorite smallish examples of the power of
coding with Ruby.

This is my favourite, here are two solutions for the task
“Write a threaded server that offers the time”
(Ruby example is taken from the book ‘The Ruby Way’):

Ruby

require “socket”

server = TCPServer.new(12345)

while (session = server.accept)
Thread.new(session) do |my_session|
my_session.puts Time.new
my_session.close
end
end

// And the functional equivalent in Java:
package at.martinus;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Date;

public class TimeServer {
private static class TellTime extends Thread {
private Socket soc;

 public TellTime(Socket soc) {
   super();
   this.soc = soc;
 }

 public void run() {
   try {
     this.soc.getOutputStream().write(new

Date().toString().getBytes());
} catch (Exception e) {
} finally {
try {
this.soc.close();
} catch (IOException e1) {
}
}
}
}

public static void main(String args[]) throws Exception {
ServerSocket server = new ServerSocket(12345);
while (true) {
new TellTime(server.accept()).start();
}
}
}

hcatlin · December 1, 2005, 10:59pm

How about an application which uses open-uri or Net::HTTP to download
all the files of a particular type from a web-page? For example, all
the images, or all the linked images, or all the linked mp3 files, or
whatever. I’d recommend just using regular expressions for the HTML
parsing, since that will show the power of regular expressions and
will also avoid the potential of Ruby XML parsing libraries barfing on
bad HTML.

The URI library can be used to handle relative URLs, etc.

This will be a good demo, and useful too.

Another option is a bulk-downloader that takes special URLs like
http://www.somesite.com/images/image_[01-25].jpg to get all the images
from image_01.jpg to image_25.jpg.

Ryan

hcatlin · December 1, 2005, 11:07pm

James, that’s more what I’m thinking about.

Less libraries, and more how powerful its paradigms are. Especially its
unique syntax and how readable it is (when done right).

Thanks everyone for your suggestions though. They are very good.

hcatlin · December 2, 2005, 1:05am

Since the audience is composed of CS majors, some classic algorithms in
ruby vs java or C might be in order. Also you might show them the
buildup of a multi-level data structure, then dump and retrieve using
yaml…

hcatlin · December 2, 2005, 3:18am

Show them the basics of the language, ALA “Ruby in a Nutshell”.
Let them loose with irb & ri.

hcatlin · December 6, 2005, 6:43am

Hi Hampton,

What I’m asking you guys for is if you have any short code ideas that
can be programmed really quickly in Ruby that might illustrate its
versatility. Some code example that would be hell to write in other
languages that would be interesting for an hour long explaination.

My favorite is the well-known quicksort algorithm:

def quicksort(a)
return a if a.size <= 1
pivot = a[0]
quicksort(a.select {|i| i < pivot }) +
a.select {|i| i == pivot } +
quicksort(a.select {|i| i > pivot })
end

quicksort is “hell” to write in C or C++ unless you’re extremely clever.

Wayne V.
No Bugs Software
“Ruby and C++ Agile Contract Programming in Silicon Valley”

hcatlin · December 6, 2005, 4:19pm

On 12/6/05, Wayne V. [email protected] wrote:

        a.select {|i| i == pivot } +
quicksort(a.select {|i| i > pivot })
end

quicksort is “hell” to write in C or C++ unless you’re extremely clever.

Wayne V.
No Bugs Software
“Ruby and C++ Agile Contract Programming in Silicon Valley”

And then demonstrate how this actually works with all kinds of objects
that
implement the comparison operators .
Nice duck typing example.

Han

hcatlin · December 7, 2005, 6:02am

On Dec 6, 2005, at 12:47 PM, gabriele renzi wrote:

pivot = a[0]
pivot = a.shift
less, more = a.partition{|y| y < pivot}
qs(less) + [pivot] + qs(more)
end

I don’t know, if you start throwing partition in there, you’re this
close to just saying a.sort

hcatlin · December 6, 2005, 6:50pm

Wayne V. ha scritto:

def quicksort(a)
return a if a.size <= 1
pivot = a[0]
quicksort(a.select {|i| i < pivot }) +
a.select {|i| i == pivot } +
quicksort(a.select {|i| i > pivot })
end

quicksort is “hell” to write in C or C++ unless you’re extremely clever.

you may appreciate Enumerable#partition:
def qs(a)
return a if a.size <=1
pivot = a.shift
less, more = a.partition{|y| y < pivot}
qs(less) + [pivot] + qs(more)
end