ruby and oo for beginners
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Ruby and OO
Cory Foy | @cory_foyhttp://www.coryfoy.com
Triangle.rb
June 24, 2014
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Overview• What is Ruby?• Ruby Basics• Advanced Ruby• Wrap-up
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
What is Ruby?• First released in 1995 by Yukihiro
Matsumoto (Matz)• Object-Oriented
– number = 1.abs #instead of Math.abs(1)• Dynamically Typed
– result = 1+3
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
What is Ruby?
• http://www.rubygarden.org/faq/entry/show/3
class Person attr_accessor :name, :age # attributes we can set and retrieve def initialize(name, age) # constructor method @name = name # store name and age for later retrieval @age = age.to_i # (store age as integer) end def inspect # This method retrieves saved values "#{@name} (#{@age})" # in a readable format end end
p1 = Person.new('elmo', 4) # elmo is the name, 4 is the age puts p1.inspect # prints “elmo (4)”
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Will It Change Your Life?• Yes!• Ok, Maybe• It’s fun to program with• And what is programming if it isn’t fun?
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics• Variables, Classes and Methods• Properties / Attributes• Exceptions• Access Control• Importing Files and Libraries• Duck Typing
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Variables• Local (lowercase, underscores)
– fred_j = Person.new(“Fred”)
• Instance (@ sign with lowercase)– @name = name
• Class (@@ with lowercase)– @@error_email = “testing@test.com”
• Constant (Starts with uppercase)– MY_PI = 3.14– class Move
• Global ($ with name)– $MEANING_OF_LIFE = 42
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Variables contain references to objects
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Classes
• Class definitions are started with class,are named with a CamelCase name, and ended with end
class Move attr_accessor :up, :right def initialize(up, right) @up = up @right = right endend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Classes (and Modules) are Objects
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Classes
• Attributes and fields normally go at the beginning of the class definition
class Move attr_accessor :up, :right def initialize(up, right) @up = up @right = right endend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Classes
• initialize is the same concept as a constructor from .NET or Java, and is called when someone invokes your object using Move.new to set up the object’s state
class Move attr_accessor :up, :right def initialize(up, right) @up = up @right = right endend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Methods
• Methods return the last expression evaluated. You can also explicitly return from methods
class Move def up @up end
def right return @right endend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Every Expression Evaluates to an Object
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Methods
• Methods can take in specified parameters, and also parameter lists (using special notation)
class Move def initialize(up, right) @up = up @right = right endend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
It’s All About Sending Messages to Objects
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Methods
• Class (“Static”) methods start with either self. or Class.
class Move def self.create return Move.new end
def Move.logger return @@logger endend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Properties• Ruby supports the concept of
Properties (called Attributes)class Move def up @up endend
class Move def up=(val) @up = val endend
move = Move.newmove.up = 15puts move.up #15
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Properties• Ruby also provides convenience
methods for doing thisclass Move attr_accessor :up #Same thing as last slideend
move = Move.newmove.up = 15puts move.up #15
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Properties• You can specify read or write only
attributes as wellclass Move attr_reader :up #Can’t write attr_writer :down #Can’t readend
move = Move.newmove.up = 15 #errord = move.down #error
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Exceptions• Ruby has an Exception hierarchy• Exceptions can be caught, raised and
handled• You can also easily retry a block of
code when you encounter an exception
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Exceptionsprocess_file = File.open(“testfile.csv”)
begin #put exceptional code in begin/end block #...process file rescue IOError => io_error puts “IOException occurred. Retrying.” retry #starts block over from begin rescue => other_error puts “Bad stuff happened: “ + other_error else #happens if no exceptions occur puts “No errors in processing. Yippee!” ensure # similar to finally in .NET/Java process_file.close unless process_file.nil?end
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Access Control
• Ruby supports Public, Protected and Private methods
• Private methods can only be accessed from the instance of the object, not from any other object, even those of the same class as the instance
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Access Control• Access is controlled by using keywords
class Move private def calculate_move end #Any subsequent methods will be private until.. public def show_move end #Any subsequent methods will now be publicend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Access Control• Methods can also be passed as args
class Move def calculate_move end
def show_move end
public :show_move protected :calculate_moveend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Imports• To use a class from another file in your
class, you must tell your source file where to find the class you want to use
require ‘calculator’class Move def calculate_move return @up * Calculator::MIN_MOVE endend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics - Imports• There are two types of imports
– require• Only loads the file once
– load• Loads the file every time the method is executed
• Both accept relative and absolute paths, and will search the current load path for the file
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Duck Typing• What defines an object?• How can you tell a car is a car?
– By model?– By name?
• Or, by it’s behavior?
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Duck Typing
• We’d use static typing! So only the valid object could be passed in
• What if my object has the same behavior as a Car?
class CarWash def accept_customer(car)
endend
• How would we validate this in .NET or Java?
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Duck Typing• What is
this?
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Duck Typing• How
about this?
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Duck Typing• What
about this?
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Duck Typing• We know objects based on the behaviors and attributes the object possesses
• This means if the object passed in can act like the object we want, that should be good enough for us!
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Duck Typing
• Or we could just let it fail as a runtime error
Class CarWash def accept_customer(car) if car.respond_to?(:drive_to) @car = car wash_car else reject_customer end endend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Blocks• A block is just a section of code
between a set of delimters – { } or do..end
{ puts “Ho” }
3.times do puts “Ho “end #prints “Ho Ho Ho”
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Blocks• Blocks can be associated with method invocations.
The methods call the block using yielddef format_print puts “Confidential. Do Not Disseminate.” yield puts “© SomeCorp, 2006”end
format_print { puts “My name is Earl!” } -> Confidential. Do Not Disseminate. -> My name is Earl! -> © SomeCorp, 2006
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Blocks• We can check to see if a block was passed to our
methoddef MyConnection.open(*args) conn = Connection.open(*args) if block_given? yield conn #passes conn to the block conn.close #closes conn when block finishes end
return connend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Iterators• Iterators in Ruby are simply methods
that can invoke a block of code• Iterators typically pass one or more
values to the block to be evaluated
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Iteratorsdef fib_up_to(max) i1, i2 = 1, 1 while i1 <= max yield i1 i1, i2 = i2, i1+i2 # parallel assignment endend
fib_up_to(100) {|f| print f + “ “}
-> 1 1 2 3 5 8 13 21 34 55 89
• Pickaxe Book, page 50
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Modules• At their core, Modules are like
namespaces in .NET or Java.module Kite def Kite.fly endend
module Plane def Plane.fly endend
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Mixins• Modules can’t have instances – they
aren’t classes• But Modules can be included in
classes, who inherit all of the instance method definitions from the module
• This is called a mixin and is how Ruby does “Multiple Inheritance”
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Mixinsmodule Print def print puts “Company Confidential” yield endend
class Document include Print #...end
doc = Document.newdoc.print { “Fourth Quarter looks great!” } -> Company Confidential -> Fourth Quarter looks great!
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Reflection• How could we call the Length of a
String at runtime in .NET?String myString = "test";int len = (int)myString .GetType() .InvokeMember("Length", System.Reflection.BindingFlags.GetProperty, null, myString, null);Console.WriteLine("Length: " + len.ToString());
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Reflection• In Ruby, we can just send the
command to the objectmyString = “Test”puts myString.send(:length) # 4
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Advanced Ruby - Reflection• We can also do all kinds of fancy stuff#print out all of the objects in our systemObjectSpace.each_object(Class) {|c| puts c}
#Get all the methods on an object“Some String”.methods
#see if an object responds to a certain methodobj.respond_to?(:length)
#see if an object is a typeobj.kind_of?(Numeric)obj.instance_of?(FixNum)
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Sending Can Be Very, Very Bad
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Basics – Other Goodies• RubyGems – Package Management for
Ruby Libraries• Rake – A Pure Ruby build tool (can use
XML as well for the build files)• RDoc – Automatically extracts
documentation from your code and comments
Thursday, June 26, 14
Triangle.rb MeetupJune 25th, 2012
Cory Foy | @cory_foyhttp://www.coryfoy.comRuby and OO
Ruby Resources• Programming Ruby by Dave Thomas (the
Pickaxe Book)• http://www.ruby-lang.org• http://www.rubycentral.org• http://www.ruby-doc.org• http://www.triangleruby.com• http://www.manning.com/black3/• http://www.slideshare.net/dablack/wgnuby
Thursday, June 26, 14
Cory Foyfoyc@coryfoy.com
@cory_foy
blog.coryfoy.com
prettykoolapps.com
coryfoy.com
Thursday, June 26, 14
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