Ruby

What is Ruby?Programming LanguageObject-orientedInterpreted

Popular- Ruby on Rails a framework for Web Server Programming

Interpreted LanguagesNot compiled like JavaCode is written and then directly executed

by an interpreterType commands into interpreter and see

immediate results

Computer

RuntimeEnvironmentCompilerCodeJava:

ComputerInterpreterCodeRuby:

What is Ruby on Rails (RoR)Development framework for web

applications written in Ruby Used by some of your favorite sites!

Advantages of a frameworkStandard features/functionality are built-inPredictable application organization

Easier to maintainEasier to get things going

InstallationWindows

Navigate to: http://www.ruby-lang.org/en/downloads/

Scroll down to "Ruby on Windows"Download the "One-click Installer"Follow the install instructions

Include RubyGems if possible (this will be necessary for Rails installation later)

Mac/LinuxOS X 10.4 ships with broken Ruby! Go here…

http://hivelogic.com/articles/view/ruby-rails-mongrel-mysql-osx

hello_world.rb

puts "hello world!"

All source code files end with .rb = ruby

NOTE: we are not really going to learn how to make general ruby programs but, in this class we will learn about Ruby on Rails ---which is a web framework for making web apps or web sites.

puts vs. print"puts" adds a new line after it is done analogous System.out.println()

"print" does not add a new lineanalogous to System.out.print()

Running Ruby Programs (via interpreter)Use the Ruby interpreter

ruby hello_world.rb“ruby” tells the computer to use the Ruby interpreter

Interactive Ruby (irb) consoleirb

Get immediate feedbackTest Ruby features

NOTE: we are not really going to learn how to make general ruby programs but, in this class we will learn about Ruby on Rails ---which is a web framework for making web apps or web sites.

Comments# this is a single line comment

=beginthis is a multiline commentnothing in here will be part of the code

=end

Variables

Declaration – No need to declare a "type"

Assignment – same as in JavaExample: (like javascript)

x = "hello world" # Stringy = 3 # Fixnumz = 4.5 # Floatr = 1..10 # Range

Variable Names and Scopesfoo Local variable$foo Global variable@foo Instance variable in object@@foo Class variableMAX_USERS “Constant” (by convention)

Difference between instance and “class” variables

Instance variables are scoped within a specific instance.

instance variable title, each post object will have its own title.

Class variables , instead, is shared across all instances of that class.

class Post def initialize(title) @title = title end

def title @title endend

p1 = Post.new("First post")p2 = Post.new("Second post")

p1.title# => "First post"p2.title# => "Second post"

class Post @@blog = "The blog“

# previous stuff for title here…….

def blog @@blog end

def blog=(value) @@blog = value endend

p1.blog# => "The blog"p2.blog# => "The blog“p1.blog = "New blog" p1.blog # => "New blog"p2.blog # => "New blog"

ObjectsEverything is an object.

Common Types (Classes): Numbers, Strings, Ranges

nil, Ruby's equivalent of null is also an object

Uses "dot-notation" like Java objectsYou can find the class of any variable

x = "hello"x.class String

You can find the methods of any variable or class

x = "hello"x.methodsString.methods

String Literals“How are you today?”

Single quotes (only \' and \\)'Bill\'s "personal" book'

Double quotes (many escape sequences)"Found #{count} errors\nAborting job\n"

%q (similar to single quotes)%q<Nesting works: <b>Hello</b>>

%Q (similar to double quotes)%Q|She said "#{greeting}"\n|

“Here documents”<<ENDFirst lineSecond lineEND

Ruby String Syntax

Equalities

x = Array.new # how to declare an arrayx << 10x[0] = 99y = ["Alice", 23, 7.3]x[1] = y[1] + y[-1]

ary = Array.new #sets to empty array [] Array.new(3) #sets to length of 3 [nil, nil, nil] Array.new(3, true) #sets to length of 3 [true, true, true]

person = Hash.newperson["last_name"] = "Rodriguez"person[:first_name] = "Alice“

order = {"item" => "Corn Flakes", "weight" => 18}order = {:item => "Corn Flakes", :weight => 18}order = {item: "Corn Flakes", weight: 18}

Arrays and Hashes

Hashes – Starting the Zombies exampleFrom http://railsforzombies.org/

Arrays ---accessing elementsarr = [1, 2, 3, 4, 5, 6] arr[2] # 3 arr[100] # nil arr[-3] # 4 arr[2, 3] # [3, 4, 5] –means start index 2 and get 3 elements

arr[1..4] # [2, 3, 4, 5] –means start index 1 through 4 index

Also, arr.first and arr.last

array = [14, 22, 34, 46, 92]for value in array do ...end

Objects (cont.)There are many methods that all Objects

haveInclude the "?" in the method names, it is

a Ruby naming convention for boolean methods

nil?eql?/equal? (3.eql?2)==, !=, ===instance_of?is_a?to_s

NumbersNumbers are objectsDifferent Classes of Numbers

FixNum, Float3.eql?2 false-42.abs 423.4.round 33.6.round 43.2.ceil 43.8.floor 33.zero? false

Booleannil or false = falseEverything else = true

String Methods"hello world".length 11

"hello world".nil? false

"".nil? false

"ryan" > "kelly" true

"hello_world!".instance_of?String true

"hello" * 3 "hellohellohello"

"hello" + " world" "hello world"

"hello world".index("w") 6

Operators and LogicSame as Java

* , / , +, - Also same as Java

"and" and "or" as well as "&&" and "||"Strings

String concatenation (+)String multiplication (*)

Conditionals: if/elsif/else/endMust use "elsif" instead of "else if"Notice use of "end". It replaces closing

curly braces in JavaExample:

if (age < 35)puts "young whipper-snapper"

elsif (age < 105)puts "80 is the new 30!"

elseputs "wow… gratz..."

end

Inline "if" statementsOriginal if-statement

if age < 105puts "don't worry, you are still young"

end

Inline if-statementputs "don't worry, you are still young" if age < 105

Case Statementsgrade = case score when 0..60: ‘F’ when 61..70: ‘D’ when 71..80: ‘C’ when 81..90: ‘B’ when 90..100: ‘A’end

for-loops for-loops can use ranges Example 1:

for i in 1..10puts i

end

for-loops and rangesYou may need a more advanced range for your for-loop

Bounds of a range can be expressions

Example:for i in 1..(2*5)

puts iend

Out of blocks or loops: break, redo, next, retry

while-loops

Cannot use "i++"Example:

i = 0while i < 5

puts ii = i + 1

end

Example little routine

sum = 0i = 1while i <= 10 do sum += i*i i = i + 1endputs "Sum of squares is #{sum}\n"

Newline is statement separator

do ... end instead of { ... }

Optional parenthesesin method invocation

Substitution instring value

No variable declarations

unless"unless" is the logical opposite of "if"

Example:unless (age >= 105) # if (age < 105)puts "young."

elseputs "old."

end

untilSimilarly, "until" is the logical opposite

of "while"Can specify a condition to have the

loop stop (instead of continuing)Example

i = 0until (i >= 5) # while (i < 5), parenthesis not required

puts Ii = i + 1

end

MethodsStructure

def method_name( parameter1, parameter2, …)

statementsend

Simple Example:def print_ryan

puts "Ryan"end

ParametersNo class/type required, just name

them!Example:

def cumulative_sum(num1, num2)sum = 0for i in num1..num2

sum = sum + iendreturn sum

end

# call the method and print the resultputs(cumulative_sum(1,5))

ReturnRuby methods return the value of

the last statement in the method, so…

def add(num1, num2)sum = num1 + num2return sum

end

can becomedef add(num1, num2)

num1 + num2end

Method with array as parameterdef max(first, *rest) result= first for x in rest do if (x > result) then result= x end end return resultend

Modules – require one .rb file into another

Modules: Grouping of methods, classes, constants that make sense together…a bit like a library

User Input"gets" method obtains input from a

userExample

name = getsputs "hello " + name + "!"

Use chomp to get rid of the extra lineputs "hello" + name.chomp + "!"

chomp removes trailing new lines

Changing typesYou may want to treat a String a

number or a number as a Stringto_i – converts to an integer (FixNum)to_f – converts a String to a Floatto_s – converts a number to a String

Examples"3.5".to_i 3"3.5".to_f 3.53.to_s "3"

ConstantsIn Ruby, constants begin with an

UppercaseThey should be assigned a value at most

onceThis is why local variables begin with a

lowercaseExample:

Width = 5def square

puts ("*" * Width + "\n") * Widthend

Handling Exceptions: Catch Throw

def sample # a silly method that throws and exception x=1 throw :foo if x==1end

begin puts ‘start’ sample # call above method puts ‘end’rescue puts ‘exception found’end

General format of handling exceptions

begin  

   # -  code that could cause exception

rescue OneTypeOfException  

   # -  code to run if OneTypeException

rescue AnotherTypeOfException  

   # -  code to run if AnotherTypeOfException

else  

   # code to run for Other exceptions  

end  

Classes

Slide 46

Simple Classclass Point def initialize(x, y) @x = x @y = y end def x #defining class variable

@x end def x=(value) @x = value endend

#code using class

p = Point.new(3,4)puts "p.x is #{p.x}"p.x = 44

Another class - Bookclass Book    def initialize(title, author, date)        @title = title #various variables        @author = author        @date = date    end    def to_s #method to make string    "Book: #@title by #{@author} on #{@date}"   endend

Book class—adding methods to access class variables (setter/getter)class Book    def initialize(title, author, date) # constructor        @title = title        @author = author        @date = date    end   def author #method to access class variable author    @author  end    def author=(new_author) #method to set value of class variable author    @author = new_author  endend

Class Inheritance (calling parent-super)

class Book    def initialize(title, author, date)        @title = title        @author = author        @date = date    end   def to_s    "Book: #@title by #{@author} on #{@date}"  endend 

 class ElectronicBook < Book  def initialize(title, author, date, format)    super(title, author, date)    @format = format  end  def to_s    super + " in #{@format}"  endend 

Protection Types –here for methos

class Foo    def method1    end     def method2    end    ....    public    :method1, method3    protected    :method2    private        :method4, method5end

Public Methods: Public methods can be called by anyone. Methods are public by default except for initialize, which is always private.

Private Methods: Private methods cannot be accessed, or even viewed from outside the class. Only the class methods can access private members.

Protected Methods: A protected method can be invoked only by objects of the defining class and its subclasses. Access is kept within the family.

Creating a method operator called <(w/test class showing using it)

class Book

  attr_reader :title

    def initialize(title, author, date)

        @title = title

        @author = author

        @date = date

    end

 

  def <(book)

    return false if book.kind_of(Book)

    title < book.title

  end

end

require 'test/unit'require 'book' class TestExample < Test::Unit::TestCase  def test_operator    cat = Book.new("Cat", "Me", "1990")    dog = Book.new("Dog", "Me", "1990")    assert( cat < dog)  endend

File I/O file = File.open('testFile')

while line = file.gets

puts line

end

file.close

File.open('testFile') do |file|

while line = file.gets

puts line

end

end

File.open('testFile') do |file|

file.each_line {|line| puts line}

end

IO.foreach('testFile') {|line| puts line}

puts IO.readlines('testFile')

array = IO.readlines('testFile')

r read-only, start at beginning of file

r+ read/write, start at beginning of file

w write-only, start at beginning of file

w+ read/write, start at beginning of file

a write-only, append to end of file

a+ read/write, start at end of file

b Binary mode, Windows only, combine with above

mode = 'a'

File.open('testFile', mode) do |file|

file.print 'cat'

file.puts 'dog'

file.puts 5

end

File.open('testFile', mode) do |file|

file << 'cat' << "dog\n" << 5 << "\n"

end

Threadsrequire 'net/http'

pages = %w{ www.yahoo.com www.google.com slashdot.org}

threads = []

for page_to_fetch in pages

threads << Thread.new(page_to_fetch) do |url|

browser = Net::HTTP.new(url, 80)

puts "Fetching #{url}"

response = browser.get('/', nil)

puts "Got #{url}: #{response.message}"

end

end

threads.each {|thread| thread.join }

Fetching www.yahoo.com Fetching www.google.comFetching slashdot.org

Got www.yahoo.com: OKGot www.google.com: OKGot slashdot.org: OK

Note: Thread and HTTP are classes in ruby

NOTE: General code to create thread & associate running code (do block) and join it to thread pool

thread = Thread.new do #code to execute in Thread running end

thread.join

ReferencesWeb Sites

http://www.ruby-lang.org/en/ http://rubyonrails.org/

BooksProgramming Ruby: The Pragmatic

Programmers' Guide (http://www.rubycentral.com/book/)

Agile Web Development with RailsRails RecipesAdvanced Rails Recipes