3. What is Ruby?
• Created by Yukihiro “Matz” Matsumoto
> Started around 1993, about the same time as Java
• What is a scripting language?
> No compilation unit
puts “Hello world”
> Not compiled
> Specialized syntax and data types
subject.gsub(/before/, quot;afterquot;)
> Maybe dynamic typing /duck typing
• Design to put the “fun” back into programming
3
5. A Typical Ruby Class
class Song Properties
@@plays = 0
attr_accessor :name, :artist, :duration
def initialize(d, a, d)
@name = n; @artist = a; @duration = d
end
Constructor public
def duration_in_minutes
@duration / 60
No return end Virtual properties
def duration_in_minutes=(v)
@duration = (v * 60)
end Interpolated values
def play
@@plays += 1
puts quot;#{@name} plays #{@@plays}quot;
@@plays
end
5
end
7. Symbols
• :a_name is symbol, think identities
> Refer to the name a_name, not the value that a_name
may potentially hold
• Typically used in maps, property declaration,
method names, any place you need a name/symbol
:foo foo
Symbol table
foo
Memory location
bar
7
8. Example Use of Symbols
attr_accessor :color, :age, :name Attribute
protected :deposit, :withdrawl Access modifiers
color = {
:red => 0xf00, Maps
:green => 0x0f0,
:blue => 0x00f As keyword parameters
}
add_column :plugins, :price, :decimal,
:precision => 8, :scale => 2, :default => 0
8
9. Everything Returns a Value
• Returned not required
def duration_in_minutes
@duration / 60
end
• Statements can be used as expressions
gt = if (x > y) true else false
• Even defining a method has a return value
> Returns nil
9
10. Everything Is An Object
• 'Primitives' are objects
> -1.abs
• nil is an object
> nil.methods
• Classes are objects
> Song.new – invoking the new method on 'Song' object
> Create instances of themselves
• Code blocks are objects
> They can be pass around, even as parameters
> Blocks can be closure
10
11. Customization with Closure
class ColorButton
attr_accessor :label, :r, :g, :b
def initialize(l)
label = 1
r = 0x0f
g = 0x0f
b = 0x0f
if block_given?
yield self
end
end b = ColorButton(“Press me”) do |button|
button.r = 0xff
# more stuff
...
end 11
12. Common Uses of Closures
• Iteration
[1,2,3].each {|i| puts i }
• Resource management
File.new(quot;/etc/hostsquot;, quot;rquot;).each {|e| puts e }
• Callbacks
widget.on_button_press { puts quot;Button Pressquot; }
• Initialization
a = Array.new(5) {|i| i * i }
From http://onestepback.org/articles/10things/item3.html 12
13. Almost Everything is a Method Call
• In lots of cases, invoking method without knowing it
array[i] = 0 – invoking the [] method
1 + 2 + 3 – 1.+(2.+(3))
str.length
• Methods can be invoked with or without parenthesis
> Most developers chose the latter
> Code looks more natural especially if you are doing DSL
• Methods can be overridden
> Get operator overloading for free
13
14. Every Method Call is a Message
• obj.method(param) means having a method on the
object in Java
• In Ruby, this means sending a message to the
object
obj.send(:method, param)
is to send a '+' message with one value
1+2+3
1.send(:+, 2.send(:+, 3))
• Use respond_to? to find out if an object knows how
to handle a message
1.respond_to? :succ => true
14
15. So What Is the Big Deal?
public VCR
def initialize varag
@messages = []
end
def method_missing(method, *args, &block)
@messages << [method, args, block]
end Push triplet onto array
def play_back_to(obj)
@messages.each do |method, args, block|
obj.send(method, *args, &block)
end
end
end
From http://onestepback.org/articles/10things/page017.html 15
16. Example of Macro at the Language Level
vcr = VCR.new
vcr.sub!(/Java/) { |match| match.reverse }
vcr.upcase! Capture a group of
vcr[11,5] = quot;Universequot; operations. Reapply
vcr << quot;!quot; these on a separate
object
string = quot;Hello Java Worldquot;
puts string
vcr.play_back_to(string)
puts string # => quot;Hello AVAJ Universequot;
16
17. Duck Typing Instead of Interfaces
• Familiar with the idea of using interface to enforce
contracts
> An object can only be considered a thread if it
implements Runnable
• If an object can behave like a thread, then should
be considered as a thread
> Runnable is irrelevant if it has run()
> If it walks like a duck, talks like a duck, then we can treat
it as a duck
d = DuckLikeObject.new
puts d.quack if d.responds_to :quack
17
18. Reuse – Inheritance
• Supports inheritance
class KaraokeSong < Song
...
def to_s
super + “[#{@lyrics}]”
end
18
19. Reuse - Mixins
• Multiple inheritance like mechanism call mixins
defined by modules
> A namespace
> Can have methods
> But cannot be instantiated
• Becomes part of a class when included a module is
included in a class
> The reverse is also possible by extending the module
with an object
19
20. Mixin Example
module Stringify class MyNumber
def stringify include Stringify
if @value == 1 def initialize(value)
quot;Onequot; @value = value
elsif @value == 2 end
quot;Twoquot; ...
elsif @value == 3
quot;Threequot;
end
end
end
Stringify example http://www.juixe.com/techknow/index.php/2006/06/15/mixins-in-ruby/ 20
21. Reuse – Modifying Existing Class
• Methods can be added to a class at any time
> Applies to built in classes
• Can be frozen
class String
def rot13
self.tr(quot;A-Ma-mN-Zn-zquot;,quot;N-Zn-zA-Ma-mquot;)
end
end
“hello world”.rot13 #=> uryyb jbeyq
21
22. Extremely Flexible and Dynamic
• One of the hallmarks of scripting languages
• Metaprogramming – programs that write or
manipulate themselves
• Some of the stuff you can do
> Trap missing methods and add them if you so desire
> Kernel definition hooks eg. Adding a method
> Create code and execute them on the fly
22
23. Example of Ruby's Malleability
class Foo
def method_missing(name, *args)
if args[0].is_a?(Proc)
self.class.instance_eval do
define_method(name.to_s.chomp(quot;=quot;), args[0])
end
else
super
end
end f = Foo.new
end f.greet = lambda {|t| quot;Hello #{t}!quot;}
f.greet quot;Hello SunTech Daysquot;
Adapted from http://tech.rufy.com/2006/08/dynamically-add-methods-to-classes.html
23
24. DSLs with Ruby
• DSL is a language designed for a specific domain
> Captures jargon in language
• Ruby's DSL is internal (Fowler)
> Morph language into DSL
> Java is external and/or API based
• Killer features for DSL with Ruby
> Paranthesis-less method invocation
> Closures
> Malleable and dynamc engine
> Variable argument list
> Symbols
24
25. DSL Example
PBJ Sandwich recipe quot;PBJ Sandwichquot;
ingredients: ingredients :bread 2.slice
- two slices of bread ingredients :peanut_butter 1.spoon
- one tablespoon of peanut butter ingredients :jam 1.teaspoon
- one teaspoon of jam instructions do
step 1 “spread peanut butter”
instructions: step 2 “spread jam...”
- spread peanut butter on bread step 3 “place other slice...”
- spread jam on top of peanut butter end
- place other slice of bread on top
servings 1
prep_time 2.minutes
servings: 1
prep time: 2 minutes
Adapted from http://weblog.jamisbuck.org/2006/4/20/writing-domain-specific-languages
25
26. This is great, but...
• Ruby language is different from Java
• Ruby platform is different from Java
• How can Java developers benefit?
26
27. JRuby
• Implementation of Ruby written in Java
• Compatible with Ruby 1.8.6
• Enables use of Java code in Ruby
• Easier deployment
• More libraries
• More platforms
• Less “political” resistence
27
28. FreeTTS Example
• In Java
VoiceManager vm = VoiceManager.getInstance();
Voice voice = vm.getVoice(quot;kevin16quot;);
voice.allocate();
voice.speak(jTextArea1.getText());
voice.deallocate();
• In Ruby
require 'java'
vm = com.sun.speech.freetts.VoiceManager.getInstance()
voice = vm.getVoice(quot;kevin16quot;)
voice.allocate()
voice.speak(quot;Calling Java code from Rubyquot;)
voice.deallocate()
• JRuby engine available through JSR-223 in JavaSE 6 28
30. 3. Inserting New or Existing Slides
● To add a new slide to your presentation, select
Insert>Slide. You can also duplicate slides in the
Slide Sorter using copy and paste.
● To add a slide(s) from another presentation,
copy and paste from one file to the other in
the Slide Sorter.
● To insert an entire presentation, select Insert>File.
30
31. Template – Text Slide
with Two Line Title and Subtitle
This is a Subtitle with Initial Caps Each Major Word
• To insert a Subtitle on other slides, copy and paste
the Subtitle text block
• On a slide with a two line Title and Subtitle (as
shown here) move the bullet text block down to
make room for the Subtitle. You can also duplicate
this slide and replace the content.
31
