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
:) !