Ruby What is Ruby Programming Language Objectoriented Interpreted

Ruby

What is Ruby? Programming Language Object-oriented Interpreted Popular- Ruby on Rails a framework for Web Server Programming

Interpreted Languages Not compiled like Java Code is written and then directly executed by an interpreter Type commands into interpreter and see immediate results Java: Ruby: Code Compiler Code Runtime Environment Computer Interpreter Computer

What is Ruby on Rails (Ro. R) Development framework for web applications written in Ruby Used by some of your favorite sites!

Advantages of a framework Standard features/functionality are built-in Predictable application organization Easier to maintain Easier to get things going

Installation Windows 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 Ruby. Gems if possible (this will be necessary for Rails installation later) Mac/Linux OS 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 line analogous 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 NOTE: we are not Interactive Ruby (irb) console really going to learn how to make general irb ruby programs but, in this class we will learn Get immediate feedback about Ruby on Rails --which is a web Test Ruby features framework for making web apps or web sites.

Comments # this is a single line comment =begin this is a multiline comment nothing in here will be part of the code =end

Variables Declaration – No need to declare a "type" Assignment – same as in Java Example: (like javascript) x = "hello world" y = 3 z = 4. 5 r = 1. . 10 # String # Fixnum # Float # Range

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

Difference between instance and “class” variables Instance variables are scoped within a specific instance variable title, each post object will have its own title. Class variables , instead, is shared across all instances of that class Post def initialize(title) @title = title end def title @title end p 1 = Post. new("First post") p 2 = Post. new("Second post") p 1. title # => "First post" p 2. title # => "Second post" class Post @@blog = "The blog“ # previous stuff for title here……. def blog @@blog end def blog=(value) @@blog = value end p 1. blog # => "The blog" p 2. blog # => "The blog“ p 1. blog = "New blog" p 1. blog # => "New blog" p 2. blog # => "New blog"

Objects Everything is an object. Common Types (Classes): Numbers, Strings, Ranges nil, Ruby's equivalent of null is also an object Uses "dot-notation" like Java objects You can find the class of any variable x = "hello" x. class String You can find the methods of any variable or class x = "hello"

String Literals “How are you today? ”

Ruby String Syntax Single quotes (only ' and \) 'Bill's "personal" book' Double quotes (many escape sequences) "Found #{count} errorsn. Aborting jobn" %q (similar to single quotes) %q<Nesting works: <b>Hello</b>> %Q (similar to double quotes) %Q|She said "#{greeting}"n| “Here documents” <<END First line Second line END

Equalities

Arrays and Hashes x = Array. new # how to declare an array x << 10 x[0] = 99 y = ["Alice", 23, 7. 3] x[1] = y[1] + y[-1] ary = Array. new(3) Array. new(3, true) #sets to empty array [] #sets to length of 3 [nil, nil] #sets to length of 3 [true, true] person = Hash. new person["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}

Hashes – Starting the Zombies example From http: //railsforzombies. org/

Arrays ---accessing elements arr = [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 have Include the "? " in the method names, it is a Ruby naming convention for boolean methods nil? eql? /equal? (3. eql? 2) ==, !=, === instance_of? is_a?

Numbers are objects Different Classes of Numbers Fix. Num, Float 3. eql? 2 -42. abs 3. 4. round 3. 6. round 3. 2. ceil 3. 8. floor 3. zero? false 42 3 4 4 3 false

Boolean nil or false = false Everything else = true

String Methods "hello world". length 11 "hello world". nil? false "". nil? false "ryan" > "kelly" true "hello_world!". instance_of? String "hello" * 3 "hellohello" "hello" + " world" "hello world". index("w") 6 true

Operators and Logic Same as Java * , / , +, - Also same as Java "and" and "or" as well as "&&" and "||" Strings String concatenation (+) String multiplication (*)

Conditionals: if/else/end Must use "elsif" instead of "else if" Notice use of "end". It replaces closing curly braces in Java Example: if (age < 35) puts "young whipper-snapper" elsif (age < 105) puts "80 is the new 30!" else puts "wow… gratz. . . " end

Inline "if" statements Original if-statement if age < 105 puts "don't worry, you are still young" end Inline if-statement puts "don't worry, you are still young" if age < 105

Case Statements grade = 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 can use ranges Example 1: for i in 1. . 10 puts i end

for-loops and ranges You 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 i end

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

while-loops Cannot use "i++" Example: i = 0 while i < 5 puts i i = i + 1 end

Example little routine No variable declarations sum = 0 Newline is statement separator i = 1 while i <= 10 do sum += i*i i = i + 1 do. . . end instead of {. . . } end puts "Sum of squares is #{sum}n" Optional parentheses in method invocation Substitution in string value

unless "unless" is the logical opposite of "if" Example: unless (age >= 105) puts "young. " else puts "old. " end # if (age < 105)

until Similarly, "until" is the logical opposite of "while" Can specify a condition to have the loop stop (instead of continuing) Example i = 0 until (i >= 5) required puts I i = i + 1 end # while (i < 5), parenthesis not

Methods Structure def method_name( parameter 1, parameter 2, …) statements end Simple Example: def print_ryan puts "Ryan" end

Parameters No class/type required, just name them! Example: def cumulative_sum(num 1, num 2) sum = 0 for i in num 1. . num 2 sum = sum + i end return sum end # call the method and print the result puts(cumulative_sum(1, 5))

Return Ruby methods return the value of the last statement in the method, so… def add(num 1, num 2) sum = num 1 + num 2 return sum end can become def add(num 1, num 2) num 1 + num 2 end

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

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 user Example name = gets puts "hello " + name + "!" Use chomp to get rid of the extra line puts "hello" + name. chomp + "!" chomp removes trailing new lines

Changing types You may want to treat a String a number or a number as a String to_i – converts to an integer (Fix. Num) to_f – converts a String to a Float to_s – converts a number to a String Examples "3. 5". to_i "3. 5". to_f 3. to_s 3 3. 5 "3"

Constants In Ruby, constants begin with an Uppercase They should be assigned a value at most once This is why local variables begin with a lowercase Example: Width = 5 def square puts ("*" * Width + "n") * Width end

Handling Exceptions: Catch Throw def sample # a silly method that throws and exception x=1 throw : foo if x==1 OUTPUT end start catch : foo do puts ‘start’ sample # call above method puts ‘end’ end

Simple Class class Point def initialize(x, y) @x = x @y = y end def x @x end #defining class variable def x=(value) @x = value end #code using class p = Point. new(3, 4) puts "p. x is #{p. x}" Slide 45 p. x = 44

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

Book class—adding methods to access class variables (setter/getter) class Book def initialize(title, author, date) @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 end

Class Inheritance (calling parentsuper) class Book def initialize(title, author, date) @title = title @author = author @date = date end def to_s "Book: #@title by #{@author} on #{@date}" end class Electronic. Book < Book def initialize(title, author, date, format) super(title, author, date) @format = format end def to_s super + " in #{@format}" end

Protection Types –here for methos class Foo def method 1 end def method 2 end . . public : method 1, method 3 protected : method 2 private : method 4, method 5 end

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

mode = 'a' File. open('test. File', mode) do |file| file. print 'cat' file. puts 'dog' file. puts 5 end File I/O file = File. open('test. File') while line = file. gets puts line end file. close File. open('test. File', mode) do |file| file << 'cat' << "dogn" << 5 << "n" end File. open('test. File') do |file| while line = file. gets puts line end File. open('test. File') do |file| file. each_line {|line| puts line} end IO. foreach('test. File') {|line| puts line} 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 puts IO. readlines('test. File') a+ read/write, start at end of file array = IO. readlines('test. File') b Binary mode, Windows only, combine with above

Threads require '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 threads. each {|thread| thread. join } Fetching www. yahoo. com Fetching www. google. com Fetching slashdot. org Got www. yahoo. com: OK Got www. google. com: OK Got slashdot. org: OK

References Web Sites http: //www. ruby-lang. org/en/ http: //rubyonrails. org/ Books Programming Ruby: The Pragmatic Programmers' Guide (http: //www. rubycentral. com/book/) Agile Web Development with Rails Recipes Advanced Rails Recipes