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Dynamic languages, for software craftmanship group

Reuven Lerner, profile picture
Reuven Lerner

The document discusses dynamic languages, highlighting their characteristics such as dynamic typing and flexible object models, which result in shorter and more reusable code. It contrasts dynamic languages with static languages, emphasizing that in dynamic languages, the programmer has greater control over the programming process. Examples of dynamic languages mentioned include Ruby, Python, JavaScript, and Lisp.

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Dynamic languages Reuven M. Lerner • reuven@lerner.co.il Software Craftsmanship Group, Tel Aviv March 22nd, 2011 1
Who am I? • Web developer, software architect, consultant, trainer • Linux Journal columnist since 1996 • Mostly Ruby on Rails + PostgreSQL, but also Python, PHP, jQuery, and lots more... 2
Language wars! • Static vs. dynamic languages • I’m here representing the good guys • (Just kidding. Mostly.) • Not just a different language — a different mindset and set of expectations 3
What is a dynamic language? • Dynamic typing • Usually interpreted (or JIT compiled) • Interactive shell for experimenting • Closures (anonymous code blocks) • Flexible, “living” object model • Result: Short, powerful, reusable code 4
Who is in charge? • Static language: The language is in charge, and it’s for your own good! • Dynamic language: The programmer is in charge, and changes the language to suit his or her needs 5
6
Examples • Lisp • Smalltalk • Python • Ruby • JavaScript 7
Examples • Lisp • Smalltalk • Python • Ruby • JavaScript 7
Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
Less code! • No need for variable declarations • No function parameter declarations • No function return-type declarations 9
Ahhhh! • Are you serious? • Can real software be developed without a compiler and type checking? • How can you possibly work this way? 10
Ahhhh! • Are you serious? • Can real software be developed without a compiler and type checking? • How can you possibly work this way? • Answer:Very well, thank you. 10
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Flexible collections a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
Flexible collections Integer a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
Flexible collections Integer String a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
Flexible collections Integer String Array a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
Flexible collections Integer String Array a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} Hash => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
Collections • Built-in collections (arrays, hashes) are good for most basic data structures • Only create a class when you need to! • Learning to use arrays and hashes is a key part of dynamic programming, and can save you lots of time 13
Functional tricks • collect (map) • detect (find) • select (find_all) • reject • inject 14
Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
Total cost of order • Total price of an order of books: total_price = books. inject(0) do |sum, b| sum + (b.price * b.quantity) end 17
Real-time require require 'jobs/a' require 'jobs/b' require 'jobs/c' Dir["#{Rails.root}/app/jobs/ *.rb"]. each { |file| require file } 18
Real-time require require 'jobs/a' require 'jobs/b' require 'jobs/c' Dir["#{Rails.root}/app/jobs/ *.rb"]. each { |file| require file } 18
Real-time require require 'jobs/a' require 'jobs/b' require 'jobs/c' Dir["#{Rails.root}/app/jobs/ *.rb"]. each { |file| require file } 18
Classes • Classes allow you to abstract behavior • Classes contain data and methods • It’s easy and fast to create a class 19
Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
Reflection > p.methods # or Person.instance_methods => [:po, :poc, :pretty_print, :pretty_print_cycle, :pretty_print_instance_variables, :pretty_print_inspect, :nil?, :, :, :!, :eql?, :hash, :=>, :class, :singleton_class, :clone, :dup, :initialize_dup, :initialize_clone, :taint, :tainted?, :untaint, :untrust, :untrusted?, :trust, :freeze, :frozen?, :to_s, :inspect, :methods, :singleton_methods, :protected_methods, :private_methods, :public_methods, :instance_variables, :instance_variable_get, :instance_variable_set, :instance_variable_defined?, :instance_of?, :kind_of?, :is_a?, :tap, :send, :public_send, :respond_to?, :respond_to_missing?, :extend, :display, :method, :public_method, :define_singleton_method, :__id__, :object_id, :to_enum, :enum_for, :pretty_inspect, :ri, :, :equal?, :!, :!, :instance_eval, :instance_exec, :__send__] 21
Predicates p.methods.grep(/?$/) => [:nil?, :eql?, :tainted?, :untrusted?, :frozen?, :instance_variable_defined?, :instance_of?, :kind_of?, :is_a?, :respond_to?, :respond_to_missing?, :equal?] 22
“Local” methods class Person def blah "blah" end end => nil p = Person.new p.class.instance_methods - p.class.superclass.instance_methods => [:blah] 23
“Local” methods class Person def blah "blah" end end => nil p = Person.new p.class.instance_methods - p.class.superclass.instance_methods => [:blah] 23
“Local” methods class Person def blah "blah" end end => nil p = Person.new p.class.instance_methods - p.class.superclass.instance_methods => [:blah] 23
“Local” methods class Person def blah "blah" end end => nil p = Person.new p.class.instance_methods - p.class.superclass.instance_methods => [:blah] 23
Calling methods a.length => 5 a.send(:length) => 5 a.send("length".to_sym) => 5 24
Calling methods a.length => 5 a.send(:length) => 5 a.send("length".to_sym) => 5 24
Calling methods a.length => 5 a.send(:length) => 5 a.send("length".to_sym) => 5 24
Calling methods a.length => 5 a.send(:length) => 5 a.send("length".to_sym) => 5 24
Preferences become method calls def bid_or_ask is_ask? ? :ask : :bid end trade_amount = net_basis * (end_rate.send(bid_or_ask) - start_rate.send(bid_or_ask)) 25
Preferences become method calls def bid_or_ask is_ask? ? :ask : :bid end trade_amount = net_basis * (end_rate.send(bid_or_ask) - start_rate.send(bid_or_ask)) 25
Preferences become method calls def bid_or_ask is_ask? ? :ask : :bid end trade_amount = net_basis * (end_rate.send(bid_or_ask) - start_rate.send(bid_or_ask)) 25
Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
Searching by result 'a'.what?('A') "a".upcase == "A" "a".capitalize == "A" "a".swapcase == "A" "a".upcase! == "A" "a".capitalize! == "A" "a".swapcase! == "A" [:upcase, :capitalize, :swapcase, :upcase!, :capitalize!, :swapcase!] 27
Searching by result 'a'.what?('A') "a".upcase == "A" "a".capitalize == "A" "a".swapcase == "A" "a".upcase! == "A" "a".capitalize! == "A" "a".swapcase! == "A" [:upcase, :capitalize, :swapcase, :upcase!, :capitalize!, :swapcase!] 27
Searching by result 'a'.what?('A') "a".upcase == "A" "a".capitalize == "A" "a".swapcase == "A" "a".upcase! == "A" "a".capitalize! == "A" "a".swapcase! == "A" [:upcase, :capitalize, :swapcase, :upcase!, :capitalize!, :swapcase!] 27
Searching by result 'a'.what?('A') "a".upcase == "A" "a".capitalize == "A" "a".swapcase == "A" "a".upcase! == "A" "a".capitalize! == "A" "a".swapcase! == "A" [:upcase, :capitalize, :swapcase, :upcase!, :capitalize!, :swapcase!] 27
Monkey patching! class Fixnum def *(other) self + other end end 6*5 => 11 28
Monkey patching! class Fixnum def *(other) self + other end end 6*5 => 11 28
Monkey patching! class Fixnum def *(other) self + other end end 6*5 => 11 28
Example: “Whiny nils” • Try to invoke “id” on nil, and Rails will complain @y.id RuntimeError: Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id 29
Example: RSpec it "should have a unique name" do c1 = Currency.new(@valid_attributes) c1.save! c2 = Currency.new( :name => @valid_attributes[:name], :abbreviation => 'XYZ') c1.should be_valid c2.should_not be_valid end 30
Example: RSpec it "should have a unique name" do c1 = Currency.new(@valid_attributes) c1.save! c2 = Currency.new( :name => @valid_attributes[:name], :abbreviation => 'XYZ') c1.should be_valid c2.should_not be_valid end 30
Example: RSpec it "should have a unique name" do c1 = Currency.new(@valid_attributes) c1.save! c2 = Currency.new( :name => @valid_attributes[:name], :abbreviation => 'XYZ') c1.should be_valid c2.should_not be_valid end 30
method_missing • If no method exists, then method_missing is invoked, passing the method name, args 31
Dynamic finders Reading.find_all_by_longitude_and_d evice_id(0, 3) => [#<Reading id: 46, longitude: #<BigDecimal:24439a8,'0.0',9(18)>, latitude: ... ] Reading.instance_methods.grep(/ long/) => [] 32
Dynamic finders Reading.find_all_by_longitude_and_d evice_id(0, 3) => [#<Reading id: 46, longitude: #<BigDecimal:24439a8,'0.0',9(18)>, latitude: ... ] Reading.instance_methods.grep(/ long/) => [] 32
Dynamic finders Reading.find_all_by_longitude_and_d evice_id(0, 3) => [#<Reading id: 46, longitude: #<BigDecimal:24439a8,'0.0',9(18)>, latitude: ... ] Reading.instance_methods.grep(/ long/) => [] 32
Hash methods as keys class Hash def method_missing(name, *args) if has_key?(name) self[name] end end end 33
Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
Module includes module MyStuff def self.included(klass) klass.extend(ClassMethods) end module ClassMethods def foo; end end end 37
Module includes module MyStuff def self.included(klass) klass.extend(ClassMethods) end module ClassMethods def foo; end end end 37
Module includes module MyStuff def self.included(klass) klass.extend(ClassMethods) end module ClassMethods def foo; end end end 37
Module includes module MyStuff def self.included(klass) klass.extend(ClassMethods) end module ClassMethods def foo; end end end 37
Thanks! (Any questions?) • Call me: 054-496-8405 • E-mail me: reuven@lerner.co.il • Interrupt me: reuvenlerner (Skype/AIM) 38

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Dynamic languages, for software craftmanship group

  • 1. Dynamic languages Reuven M. Lerner • reuven@lerner.co.il Software Craftsmanship Group, Tel Aviv March 22nd, 2011 1
  • 2. Who am I? • Web developer, software architect, consultant, trainer • Linux Journal columnist since 1996 • Mostly Ruby on Rails + PostgreSQL, but also Python, PHP, jQuery, and lots more... 2
  • 3. Language wars! • Static vs. dynamic languages • I’m here representing the good guys • (Just kidding. Mostly.) • Not just a different language — a different mindset and set of expectations 3
  • 4. What is a dynamic language? • Dynamic typing • Usually interpreted (or JIT compiled) • Interactive shell for experimenting • Closures (anonymous code blocks) • Flexible, “living” object model • Result: Short, powerful, reusable code 4
  • 5. Who is in charge? • Static language: The language is in charge, and it’s for your own good! • Dynamic language: The programmer is in charge, and changes the language to suit his or her needs 5
  • 6. 6
  • 7. Examples • Lisp • Smalltalk • Python • Ruby • JavaScript 7
  • 8. Examples • Lisp • Smalltalk • Python • Ruby • JavaScript 7
  • 9. Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
  • 10. Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
  • 11. Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
  • 12. Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
  • 13. Values, not variables, have types x = 5 => 5 x.class => Fixnum x = [1,2,3] => [1, 2, 3] x.class => Array 8
  • 14. Less code! • No need for variable declarations • No function parameter declarations • No function return-type declarations 9
  • 15. Ahhhh! • Are you serious? • Can real software be developed without a compiler and type checking? • How can you possibly work this way? 10
  • 16. Ahhhh! • Are you serious? • Can real software be developed without a compiler and type checking? • How can you possibly work this way? • Answer:Very well, thank you. 10
  • 17. 11
  • 18. Flexible collections a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
  • 19. Flexible collections Integer a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
  • 20. Flexible collections Integer String a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
  • 21. Flexible collections Integer String Array a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
  • 22. Flexible collections Integer String Array a = [1, 2, 'three', [4, 5, 6]] => [1, 2, "three", [4, 5, 6]] a.length => 4 a << {first_name:'Reuven', last_name:'Lerner'} Hash => [1, 2, "three", [4, 5, 6], {:first_name=>"Reuven", :last_name=>"Lerner"}] 12
  • 23. Collections • Built-in collections (arrays, hashes) are good for most basic data structures • Only create a class when you need to! • Learning to use arrays and hashes is a key part of dynamic programming, and can save you lots of time 13
  • 24. Functional tricks • collect (map) • detect (find) • select (find_all) • reject • inject 14
  • 25. Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
  • 26. Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
  • 27. Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
  • 28. Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
  • 29. Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
  • 30. Sorted username list File.readlines('/etc/passwd'). reject {|line| line =~ /^#/}. map {|line| line.split(':'). first}. sort 15
  • 31. Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
  • 32. Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
  • 33. Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
  • 34. Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
  • 35. Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
  • 36. Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
  • 37. Domain counter domains = Hash.new(0) File.readlines(list_member_file).each do |line| email, domain = line.chomp.split('@') domains[domain.downcase] += 1 end domains.sort_by {|d| -d[1] }. each {|d| puts "#{d[1]} #{d[0]}" } domains.sort_by {|d| [-d[1], d[0]] }. each {|d| puts "#{d[1]} #{d[0]}" } 16
  • 38. Total cost of order • Total price of an order of books: total_price = books. inject(0) do |sum, b| sum + (b.price * b.quantity) end 17
  • 39. Real-time require require 'jobs/a' require 'jobs/b' require 'jobs/c' Dir["#{Rails.root}/app/jobs/ *.rb"]. each { |file| require file } 18
  • 40. Real-time require require 'jobs/a' require 'jobs/b' require 'jobs/c' Dir["#{Rails.root}/app/jobs/ *.rb"]. each { |file| require file } 18
  • 41. Real-time require require 'jobs/a' require 'jobs/b' require 'jobs/c' Dir["#{Rails.root}/app/jobs/ *.rb"]. each { |file| require file } 18
  • 42. Classes • Classes allow you to abstract behavior • Classes contain data and methods • It’s easy and fast to create a class 19
  • 43. Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
  • 44. Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
  • 45. Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
  • 46. Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
  • 47. Defining classes class Person end => nil p = Person.new => #<Person:0x00000102105740> p.class => Person p.class.ancestors => [Person, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel, BasicObject] 20
  • 48. Reflection > p.methods # or Person.instance_methods => [:po, :poc, :pretty_print, :pretty_print_cycle, :pretty_print_instance_variables, :pretty_print_inspect, :nil?, :, :, :!, :eql?, :hash, :=>, :class, :singleton_class, :clone, :dup, :initialize_dup, :initialize_clone, :taint, :tainted?, :untaint, :untrust, :untrusted?, :trust, :freeze, :frozen?, :to_s, :inspect, :methods, :singleton_methods, :protected_methods, :private_methods, :public_methods, :instance_variables, :instance_variable_get, :instance_variable_set, :instance_variable_defined?, :instance_of?, :kind_of?, :is_a?, :tap, :send, :public_send, :respond_to?, :respond_to_missing?, :extend, :display, :method, :public_method, :define_singleton_method, :__id__, :object_id, :to_enum, :enum_for, :pretty_inspect, :ri, :, :equal?, :!, :!, :instance_eval, :instance_exec, :__send__] 21
  • 49. Predicates p.methods.grep(/?$/) => [:nil?, :eql?, :tainted?, :untrusted?, :frozen?, :instance_variable_defined?, :instance_of?, :kind_of?, :is_a?, :respond_to?, :respond_to_missing?, :equal?] 22
  • 50. “Local” methods class Person def blah "blah" end end => nil p = Person.new p.class.instance_methods - p.class.superclass.instance_methods => [:blah] 23
  • 51. “Local” methods class Person def blah "blah" end end => nil p = Person.new p.class.instance_methods - p.class.superclass.instance_methods => [:blah] 23
  • 52. “Local” methods class Person def blah "blah" end end => nil p = Person.new p.class.instance_methods - p.class.superclass.instance_methods => [:blah] 23
  • 53. “Local” methods class Person def blah "blah" end end => nil p = Person.new p.class.instance_methods - p.class.superclass.instance_methods => [:blah] 23
  • 54. Calling methods a.length => 5 a.send(:length) => 5 a.send("length".to_sym) => 5 24
  • 55. Calling methods a.length => 5 a.send(:length) => 5 a.send("length".to_sym) => 5 24
  • 56. Calling methods a.length => 5 a.send(:length) => 5 a.send("length".to_sym) => 5 24
  • 57. Calling methods a.length => 5 a.send(:length) => 5 a.send("length".to_sym) => 5 24
  • 58. Preferences become method calls def bid_or_ask is_ask? ? :ask : :bid end trade_amount = net_basis * (end_rate.send(bid_or_ask) - start_rate.send(bid_or_ask)) 25
  • 59. Preferences become method calls def bid_or_ask is_ask? ? :ask : :bid end trade_amount = net_basis * (end_rate.send(bid_or_ask) - start_rate.send(bid_or_ask)) 25
  • 60. Preferences become method calls def bid_or_ask is_ask? ? :ask : :bid end trade_amount = net_basis * (end_rate.send(bid_or_ask) - start_rate.send(bid_or_ask)) 25
  • 61. Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
  • 62. Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
  • 63. Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
  • 64. Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
  • 65. Define similar methods ['preview', 'applet', 'info', 'procedures', 'discuss', 'files', 'history', 'tags', 'family', 'upload', 'permissions'].each do |tab_name| define_method( "browse_#{tab_name}_tab".to_sym ) do render :layout => 'browse_tab' end end 26
  • 66. Searching by result 'a'.what?('A') "a".upcase == "A" "a".capitalize == "A" "a".swapcase == "A" "a".upcase! == "A" "a".capitalize! == "A" "a".swapcase! == "A" [:upcase, :capitalize, :swapcase, :upcase!, :capitalize!, :swapcase!] 27
  • 67. Searching by result 'a'.what?('A') "a".upcase == "A" "a".capitalize == "A" "a".swapcase == "A" "a".upcase! == "A" "a".capitalize! == "A" "a".swapcase! == "A" [:upcase, :capitalize, :swapcase, :upcase!, :capitalize!, :swapcase!] 27
  • 68. Searching by result 'a'.what?('A') "a".upcase == "A" "a".capitalize == "A" "a".swapcase == "A" "a".upcase! == "A" "a".capitalize! == "A" "a".swapcase! == "A" [:upcase, :capitalize, :swapcase, :upcase!, :capitalize!, :swapcase!] 27
  • 69. Searching by result 'a'.what?('A') "a".upcase == "A" "a".capitalize == "A" "a".swapcase == "A" "a".upcase! == "A" "a".capitalize! == "A" "a".swapcase! == "A" [:upcase, :capitalize, :swapcase, :upcase!, :capitalize!, :swapcase!] 27
  • 70. Monkey patching! class Fixnum def *(other) self + other end end 6*5 => 11 28
  • 71. Monkey patching! class Fixnum def *(other) self + other end end 6*5 => 11 28
  • 72. Monkey patching! class Fixnum def *(other) self + other end end 6*5 => 11 28
  • 73. Example: “Whiny nils” • Try to invoke “id” on nil, and Rails will complain @y.id RuntimeError: Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id 29
  • 74. Example: RSpec it "should have a unique name" do c1 = Currency.new(@valid_attributes) c1.save! c2 = Currency.new( :name => @valid_attributes[:name], :abbreviation => 'XYZ') c1.should be_valid c2.should_not be_valid end 30
  • 75. Example: RSpec it "should have a unique name" do c1 = Currency.new(@valid_attributes) c1.save! c2 = Currency.new( :name => @valid_attributes[:name], :abbreviation => 'XYZ') c1.should be_valid c2.should_not be_valid end 30
  • 76. Example: RSpec it "should have a unique name" do c1 = Currency.new(@valid_attributes) c1.save! c2 = Currency.new( :name => @valid_attributes[:name], :abbreviation => 'XYZ') c1.should be_valid c2.should_not be_valid end 30
  • 77. method_missing • If no method exists, then method_missing is invoked, passing the method name, args 31
  • 78. Dynamic finders Reading.find_all_by_longitude_and_d evice_id(0, 3) => [#<Reading id: 46, longitude: #<BigDecimal:24439a8,'0.0',9(18)>, latitude: ... ] Reading.instance_methods.grep(/ long/) => [] 32
  • 79. Dynamic finders Reading.find_all_by_longitude_and_d evice_id(0, 3) => [#<Reading id: 46, longitude: #<BigDecimal:24439a8,'0.0',9(18)>, latitude: ... ] Reading.instance_methods.grep(/ long/) => [] 32
  • 80. Dynamic finders Reading.find_all_by_longitude_and_d evice_id(0, 3) => [#<Reading id: 46, longitude: #<BigDecimal:24439a8,'0.0',9(18)>, latitude: ... ] Reading.instance_methods.grep(/ long/) => [] 32
  • 81. Hash methods as keys class Hash def method_missing(name, *args) if has_key?(name) self[name] end end end 33
  • 82. Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
  • 83. Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
  • 84. Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
  • 85. Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
  • 86. Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
  • 87. Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
  • 88. Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
  • 89. Example h = {a:1, b:2} => 3 => {:a=>1, :b=>2} h.c h[:a] => nil => 1 h[:d] = 4 h.a => 4 => 1 h.d h['c'] = 3 => 4 34
  • 90. Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
  • 91. Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
  • 92. Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
  • 93. Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
  • 94. Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
  • 95. Hash method access class Hash def method_missing(method_name, *arguments) if has_key?(method_name) self[method_name] elsif has_key?(method_name.to_s) self[method_name.to_s] else nil end end end 35
  • 96. xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
  • 97. xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
  • 98. xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
  • 99. xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
  • 100. xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
  • 101. xml.instruct! :xml, :version=>"1.0" xml.rss(:version=>"2.0"){ xml.channel{ xml.title("Modeling Commons updates") xml.link("http://modelingcommons.org/") xml.description("NetLogo Modeling Commons") xml.language('en-us') for update in @updates xml.item do xml.title(post.title) xml.description(post.html_content) xml.author("Your Name Here") xml.pubDate(post.created_on.strftime("%a, %d %b %Y %H:%M:%S %z")) xml.link(post.link) xml.guid(post.link) end end } } 36
  • 102. Module includes module MyStuff def self.included(klass) klass.extend(ClassMethods) end module ClassMethods def foo; end end end 37
  • 103. Module includes module MyStuff def self.included(klass) klass.extend(ClassMethods) end module ClassMethods def foo; end end end 37
  • 104. Module includes module MyStuff def self.included(klass) klass.extend(ClassMethods) end module ClassMethods def foo; end end end 37
  • 105. Module includes module MyStuff def self.included(klass) klass.extend(ClassMethods) end module ClassMethods def foo; end end end 37
  • 106. Thanks! (Any questions?) • Call me: 054-496-8405 • E-mail me: reuven@lerner.co.il • Interrupt me: reuvenlerner (Skype/AIM) 38