The document provides an overview of the Ruby programming language, discussing how everything in Ruby is an object, Ruby's dynamic typing, how classes are objects and class names are constants, modules and mixins, functional support through blocks and variables, and how procs and lambdas allow for deferred evaluation.

1. Ruby Programming
Language

2. About Me
> 8 years of developing experience
retail, e-commerce, logistics,
fashion, multi-media, etc.
lead developer, team leader,
project manager, functional
analysts, architect.
a runner and a mountain lover
elimi
@I ndritS

3. Why Ruby
Everything is an Object
Dynamic typing
Open
Mix-ins
Functional support
Methods vs Keywords
(Meta)programming
‘Scripting’ support
LBNL: Testing

4. Everything is
an object

5. Classical
class MyClass
def method
@v = 1
end
end
Object Class
Instance class MyClass
@v = 1 method()
Code:
obj = MyClass.new
obj.methods == MyClass.instance_methods # => true
obj.methods != MyClass.methods # => true

6. Everything is an Object
superclass
Object Module
inst class superclass superclass
class
MyClass Class
class

7. Classes
Code:
class Cls < Array
def sum
inject{ |sum, element| sum + element}
end
end

8. Classes
Code:
class Cls < Array Cls = Class.new(Array) do
def sum def sum
inject{ |sum, element| sum + element} inject{|sum, element| sum + element}
end end
end end

9. Classes
Code:
class Cls < Array Cls = Class.new(Array) do
def sum def sum
inject{ |sum, element| sum + element} inject{|sum, element| sum + element}
end end
end end

10. Classes
Code:
class Cls < Array Cls = Class.new(Array) do
def sum def sum
inject{ |sum, element| sum + element} inject{|sum, element| sum + element}
end end
end end
Classes are nothing but objects,
class names are nothing but constants.

11. Classes
Code:
class Cls < Array Cls = Class.new(Array) do
def sum def sum
inject{ |sum, element| sum + element} inject{|sum, element| sum + element}
end end
end end
! Classes are nothing but objects,
class names are nothing but constants.

12. Dynamic Typing

13. Dynamic Typing
Code:
class CreditCard
def pay; #credit code; end
end
class Cod
def pay; #cod code; end
end
class WireTransfer
def pay; #wrt code; end
end
def process(payment)
...
payment.pay
...
end

14. Ruby is an open
language by design

15. Class Opening
Code:

16. Class Opening
Code:
3.times do
class Cls
puts “Hi”
end
end

17. Class Opening
Code:
3.times do
class Cls
puts “Hi”
end
end
=> Hi
Hi
Hi

18. Class Opening
Code:
3.times do def Cls.hi
class Cls puts “Hi Class”
puts “Hi” end
end
end
=> Hi
Hi
Hi

19. Class Opening
Code:
3.times do def Cls.hi
class Cls puts “Hi Class”
puts “Hi” end
end
end
=> Hi Cls.hi #=> Hi
Hi
Hi

20. Class Opening
Code:
def Cls.hi obj1 = Cls.new
3.times do
puts “Hi Class” obj2 = Cls.new
class Cls
puts “Hi” end
def obj1.hi
end
puts “Hi”
end
end
=> Hi Cls.hi #=> Hi
Hi
Hi

21. Class Opening
Code:
def Cls.hi obj1 = Cls.new
3.times do
puts “Hi Class” obj2 = Cls.new
class Cls
puts “Hi” end
def obj1.hi
end
puts “Hi”
end
end
=> Hi Cls.hi #=> Hi obj1.hi # => Hi
Hi
Hi

22. Class Opening
Code:
def Cls.hi obj1 = Cls.new
3.times do
puts “Hi Class” obj2 = Cls.new
class Cls
puts “Hi” end
def obj1.hi
end
puts “Hi”
end
end
=> Hi Cls.hi #=> Hi obj1.hi # => Hi
Hi obj2.hi # =>
Hi NoMethodError

23. Mixins

24. Modules
Code:
module Mod
CONSTANT = 'Outer'
class Cls
CONSTANT = 'Inner'
end
end

25. Modules
Code:
module Mod
CONSTANT = 'Outer'
class Cls
CONSTANT = 'Inner'
end
end
Mod::CONSTANT => “Outer”
Mod::Cls::CONSTANT => “Inner”

26. Modules
Code:
module Mod
def my_method
'M#my_method()'
end
end
class Cls
include Mod
end
class Cls
extend Mod
end

27. Modules
Code:
module Mod
def my_method
'M#my_method()'
end
end
class Cls
include Mod Cls.new.my_method # =>“M#my_method()”
end
class Cls
extend Mod
end

28. Modules
Code:
module Mod
def my_method
'M#my_method()'
end
end
class Cls
include Mod Cls.new.my_method # =>“M#my_method()”
end
class Cls
extend Mod Cls.my_method # =>“M#my_method()”
end

29. Modules
Code:
module Mod
def my_method
'M#my_method()'
private instance
end method
end of Module
class Cls
include Mod Cls.new.my_method # =>“M#my_method()”
end
class Cls
extend Mod Cls.my_method # =>“M#my_method()”
end

30. Modules
Code:
module Mod
def my_method
'M#my_method()'
private instance
end method
end of Module
class Cls
include Mod Cls.new.my_method # =>“M#my_method()”
end
Object#extend
class Cls
extend Mod Cls.my_method # =>“M#my_method()”
end

31. Functional
Support

32. Blocks
Code:
def three_times
yield
yield
yield
end
three_times { puts "Hello" }
# =>
Hello
Hello
Hello

33. Blocks
Code:
File.open("path/file", "r") do |file|
file.each_line do |line|
name, surname = line.split(',')
...
end
end

34. Blocks
Code:
def my_method
x = “Hello”
yield("cruel")
end
x = "Goodbye"
my_method {|y| "#{x}, #{y} world" }
# => "Goodbye, cruel world"

35. Scope
Class
Module
Code: Method
v1 = 1
class Cls # SCOPE GATE: entering class
v2 = 2
local_variables # => ["v2"]
def my_method # SCOPE GATE: entering def
v3 = 3
local_variables # => ["v3"]
end # SCOPE GATE: leaving def
local_variables # => ["v2"]
end # SCOPE GATE: leaving class

36. Variables
Code:
$v1 = ‘global variable’
def Cls
v2 = ‘local variable’
@v3 = ‘class instance variable’
def my_method
@v3 = ‘instance variable’
end
@@v4 = ‘class hiearchy variable’
end

37. Blocks
Code:
def define_methods Dynamic
Method
Scope shared = 0
Flattening
Kernel.send :define_method, :counter do
shared
end
Kernel.send :define_method, :inc do |x|
shared += x
end
end
counter # => 0
inc(4)
counter # => 4

38. Proc and Lambda
Deferred
Code: Evaluation
plus_one = Proc.new {|x| x + 1 }
...
plus_one.call(2) # => 3
plus_one = lambda {|x| x + 1 }
plus_one.call(2) # => 3

39. Proc and Lambda
(& and to_proc)
Code:
[1, 2, 5].inject(0){|sum, e| sum + e} # => 8

40. Proc and Lambda
(& and to_proc)
Code:
[1, 2, 5].inject(0){|sum, e| sum + e} # => 8
[1, 2, 5].inject(0, &:+) # => 8

41. Proc and Lambda
(& and to_proc)
Code:
[1, 2, 5].inject(0){|sum, e| sum + e} # => 8
Symbol
[1, 2, 5].inject(0, &:+) # => 8

42. Proc and Lambda
(& and to_proc)
Code:
[1, 2, 5].inject(0){|sum, e| sum + e} # => 8
Symbol
[1, 2, 5].inject(0, &:+) # => 8
Class Symbol
def to_proc
proc { |obj, *args| obj.send(self, *args) }
end
end

43. Methods vs Keywords

44. Method Visibility
class Cls
! def public_method
! ! self.private_method
!end
!
! private
!
! def private_method; end
end

45. Method Visibility
class Cls
! def public_method
! ! self.private_method
!end
!
! private
!
! def private_method; end
end
C.new.public_method #=> NoMethodError: private method

46. Method Visibility
class Cls
(1..5).each do |i|
define_method(“m#{i}”){}
class Cls end
! def public_method !
! ! self.private_method public :m1, m2
!end private :m3, m4
! protected :m5 ! !
! private end
!
! def private_method; end
end
C.new.public_method #=> NoMethodError: private method

47. Method Visibility
Code: Dynamic
Dispatch
c = Cls.new
c.send :private_method
Context c.instance_eval {private_method}
Probe c.instance_eval {@var}

48. Exceptions
Code:
begin
raise “blew up”
rescue => ex
puts “I #{ex}”
end

49. Exceptions
Code: begin
...
begin fail “error”
raise “blew up” ...
rescue => ex rescue StandardError => ex
puts “I #{ex}” puts “Failed: ” + ex
end raise
else
...
ensure
# clean up
...
end

50. Exceptions
Code: begin
...
begin fail “error”
raise “blew up” ...
rescue => ex rescue StandardError => ex
puts “I #{ex}” puts “Failed: ” + ex
end raise
else
...
ensure
# clean up
tries = 0 ...
begin end
tries += 1
puts "Trying #{tries}..." raise "Didn’t work"
rescue
retry if tries < 3
puts "I give up"
end

51. Exceptions
Code: begin
...
begin fail “error”
raise “blew up” ...
rescue => ex rescue StandardError => ex
puts “I #{ex}” puts “Failed: ” + ex
end raise
else
...
ensure
Retry # clean up
tries = 0 ...
begin end
tries += 1
puts "Trying #{tries}..." raise "Didn’t work"
rescue
retry if tries < 3
puts "I give up"
end

52. Exceptions
(raise)
Code: def raise(error_cls_or_obj, msg, backtrace)
error = error_cls_or_obj.exception(msg)
#...
end

53. Exceptions
(raise)
Code: def raise(error_cls_or_obj, msg, backtrace)
error = error_cls_or_obj.exception(msg)
#...
end
# Bang!
module RaiseExit
def raise(msg_or_exc, msg=msg_or_exc, trace=caller)
warn msg.to_s
exit!
end
end
class Object
include RaiseExit
end

54. Exceptions
(dynamic rescue clauses)
Code:
ignore_exceptions(IOError, SystemCallError) do
open("NONEXISTENT_FILE")
end
def ignore_exceptions(*exceptions)
yield
rescue *exceptions => e
puts "IGNORED: ’#{e}’"
end

55. (Meta)Programming

56. (Meta)Programming
Class Macros Example
Code:
Class Customer
def name
@name
end
def name=(n)
@name = n
end
...
def age
@age
end
def age=(a)
@age = a
end
end

57. (Meta)Programming
Class Macros Example
Code:
Class Customer class Customer
def name attr_accessor :name, :surname, :age
@name end
end
def name=(n)
@name = n
end
...
def age
@age
end
def age=(a)
@age = a
end
end

58. (Meta)Programming
Class Macros Example
Code:
Class Customer class Customer
def name attr_accessor :name, :surname, :age
@name end
end
def name=(n) class Customer
@name = n def self.attr_accessor(*accessors)
end accessors.each do |accessor|
... define_method(accessor) do
instance_variable_get("@#{accessor}")
def age end
@age
end define_method("#{accessor}=") do |accessor_value|
instance_variable_set("@#{accessor}", accessor_value)
def age=(a) end
@age = a end
end end
end end

59. Hook Methods
(a.k.a. callbacks)
Method related hooks
Class and module related
hooks
• method_missing
• method_added • append_features
• method_removed • const_missing
• method_undefined • extend_object
• singleton_method_added • extended
• • included
singleton_method_removed
• • inherited
singleton_method_undefined
• initialize_copy
Object marshaling Coercion
hooks hooks
• marshal_dump • coerce
• marshal_load • induced_from
• to_xxx

60. Method Missing
Code:
config = {
:host => 'ws.contactlab.it',
:path => '/RPC2',
:use_ssl => true
}
class ContactLab
def initialize(c)
@ws_client = XMLRPC::Client.new(c)
end
def method_missing(rpc_method_name, *params)
@ws_client.call("contactlab.#{rpc_method_name}",
params)
end
end
ContactLab.new(config).addNewRecipient(recipient)

61. Scripting

62. Expressions
Code:
song_type = if song.mp3Type == MP3::Jazz
if song.written < Date.new(1935, 1, 1)
Song::TradJazz
else
Song::Jazz
end
else
Song::Other
end

63. Infrastructure as code
Code:
package "rabbimq-server" do
action :install
end
service "rabbitmq-server" do
supports :status => true, :restart => true, :reload => true
action[:enable, :start]
end

64. Testing

65. Code:
describe Stack do
RSpec
before(:each) do
@stack = Stack.new
@stack.push :item
end
describe "#peek" do
it "returns the top element" do
@stack.peek.should == :item
end
it "doesn’t remove the top" do
@stack.peek
@stack.size.should == 1
end
end
describe "#pop" do
it "returns the top element" do
@stack.pop.should == :item
end
it "removes the top element" do
@stack.pop
@stack.size.should == 0
end
end
end

66. Code:
describe Stack do
RSpec
before(:each) do
@stack = Stack.new expect {
@stack.push :item User.create!(:role => "admin")
end }.to change{ User.admins.count }.by(1)
describe "#peek" do
it "returns the top element" do
@stack.peek.should == :item
end
it "doesn’t remove the top" do
@stack.peek
@stack.size.should == 1
end
end
describe "#pop" do
it "returns the top element" do
@stack.pop.should == :item
end
it "removes the top element" do
@stack.pop
@stack.size.should == 0
end
end
end

67. Code:
describe Stack do
RSpec
before(:each) do
@stack = Stack.new expect {
@stack.push :item User.create!(:role => "admin")
end }.to change{ User.admins.count }.by(1)
describe "#peek" do
it "returns the top element" do result.should be_close(5.25, 0.005)
@stack.peek.should == :item
end
it "doesn’t remove the top" do
@stack.peek
@stack.size.should == 1
end
end
describe "#pop" do
it "returns the top element" do
@stack.pop.should == :item
end
it "removes the top element" do
@stack.pop
@stack.size.should == 0
end
end
end

68. Code:
describe Stack do
RSpec
before(:each) do
@stack = Stack.new expect {
@stack.push :item User.create!(:role => "admin")
end }.to change{ User.admins.count }.by(1)
describe "#peek" do
it "returns the top element" do result.should be_close(5.25, 0.005)
@stack.peek.should == :item
end
it "doesn’t remove the top" do expect{do_something_risky}.to raise_error /too risky/
@stack.peek
@stack.size.should == 1
end
end
describe "#pop" do
it "returns the top element" do
@stack.pop.should == :item
end
it "removes the top element" do
@stack.pop
@stack.size.should == 0
end
end
end

69. Code:
describe Stack do
RSpec
before(:each) do
@stack = Stack.new expect {
@stack.push :item User.create!(:role => "admin")
end }.to change{ User.admins.count }.by(1)
describe "#peek" do
it "returns the top element" do result.should be_close(5.25, 0.005)
@stack.peek.should == :item
end
it "doesn’t remove the top" do expect{do_something_risky}.to raise_error /too risky/
@stack.peek
@stack.size.should == 1
end array.empty?.should == true <--> array.should be_empty
end
describe "#pop" do
it "returns the top element" do
@stack.pop.should == :item
end
it "removes the top element" do
@stack.pop
@stack.size.should == 0
end
end
end

70. Code:
describe Stack do
RSpec
before(:each) do
@stack = Stack.new expect {
@stack.push :item User.create!(:role => "admin")
end }.to change{ User.admins.count }.by(1)
describe "#peek" do
it "returns the top element" do result.should be_close(5.25, 0.005)
@stack.peek.should == :item
end
it "doesn’t remove the top" do expect{do_something_risky}.to raise_error /too risky/
@stack.peek
@stack.size.should == 1
end array.empty?.should == true <--> array.should be_empty
end
describe "#pop" do field.players.select{|p| p.team == home_team}
it "returns the top element" do .length.should == 9
@stack.pop.should == :item
end
it "removes the top element" do
@stack.pop
@stack.size.should == 0
end
end
end

71. Code:
describe Stack do
RSpec
before(:each) do
@stack = Stack.new expect {
@stack.push :item User.create!(:role => "admin")
end }.to change{ User.admins.count }.by(1)
describe "#peek" do
it "returns the top element" do result.should be_close(5.25, 0.005)
@stack.peek.should == :item
end
it "doesn’t remove the top" do expect{do_something_risky}.to raise_error /too risky/
@stack.peek
@stack.size.should == 1
end array.empty?.should == true <--> array.should be_empty
end
describe "#pop" do field.players.select{|p| p.team == home_team}
it "returns the top element" do .length.should == 9
@stack.pop.should == :item
end
home_team.should have(9).players_on(field)
it "removes the top element" do
@stack.pop
@stack.size.should == 0
end
end
end

72. Code:
describe Stack do
RSpec
before(:each) do
@stack = Stack.new expect {
@stack.push :item User.create!(:role => "admin")
end }.to change{ User.admins.count }.by(1)
describe "#peek" do
it "returns the top element" do result.should be_close(5.25, 0.005)
@stack.peek.should == :item
end
it "doesn’t remove the top" do expect{do_something_risky}.to raise_error /too risky/
@stack.peek
@stack.size.should == 1
end array.empty?.should == true <--> array.should be_empty
end
describe "#pop" do field.players.select{|p| p.team == home_team}
it "returns the top element" do .length.should == 9
@stack.pop.should == :item
end
home_team.should have(9).players_on(field)
it "removes the top element" do
@stack.pop a_politician.should have_at_least(3).escorts
@stack.size.should == 0
end
end
end

73. Code:
Cucumber
Feature: Google Search
In order to learn something
As an internet user
I want to search for information on Google
Scenario: Learn about Scrat
Given I am on google.com
When I search for "Scrat"
Then I should see search results about Scrat
When /^I search for ['"](.*)['"]$/ do |query|
fill_in('q', :with => query)
click_button('Google Search')
end
Then /^I should see search results about (.*)$/
do |term|
response_body.should include(term)
end

74. The Object Model Revisited

75. Splash "motherboard" =~ /board/
class String in_place!
%w(a b c).freeze
alias :real_length :length
empty? :symbol
def length a ||= []
real_length > 5 ? 'long' : 'short'
end raise InvalidFormat unless Formats.include?(format)
end
[1,2,3].map{ |e| e * e } #=> [1,4,9]
[1,2,3].inject{|sum, e| s + e} #=> 6
[1,2,3].select{|e| e % 2 != 0} #=> [1, 3]
class Singleton RSpec
spec = Gem::Specification.new do |s|
s.name = “My Gem name” class << self
s.version = “0.0.1” def instance File.instance_methods.grep(/.*each.*/)
# ... @instance ||= new
end end
chars = "hello world".tap {|x| puts "original object: #{x.inspect}"}
.each_char .tap {|x| puts "each_char returns: #{x.inspect}"}
private :new .to_a .tap {|x| puts "to_a returns: #{x.inspect}"}
end .map {|c| c.succ } .tap {|x| puts "map returns: #{x.inspect}" }
end .sort .tap {|x| puts "sort returns: #{x.inspect}"}

76. Why Ruby?

77. Why Ruby?
Your own choice!!!

78. ns?
stio
ue
Q

79. References

80. Than
k you
:) !