Transcript Intro to Ruby

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 (RoR)
 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 RubyGems 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
 Interactive Ruby (irb) console NOTE: we are not
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
@@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.

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
end
end
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
end
end
p1.blog
# => "The blog"
p2.blog
# => "The blog“
p1.blog = "New blog"
p1.blog
# => "New blog"
p2.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"
x.methods
String.methods
String Literals
 “How are you today?”
Ruby String Syntax
 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”
<<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
Array.new(3)
Array.new(3, true)
#sets to empty array []
#sets to length of 3 [nil, nil, nil]
#sets to length of 3 [true, 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?
 to_s
Numbers
 Numbers are objects
 Different Classes of Numbers
 FixNum, 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

"hellohellohello"
"hello" + " world"

"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/elsif/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
 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)
puts I
i=i+1
end
# while (i < 5), parenthesis not required
Methods
 Structure
def method_name( parameter1, parameter2, …)
statements
end
 Simple Example:
def print_ryan
puts "Ryan"
end
Parameters
 No class/type required, just name them!
 Example:
def cumulative_sum(num1, num2)
sum = 0
for i in num1..num2
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(num1, num2)
sum = num1 + num2
return sum
end
can become
def add(num1, num2)
num1 + num2
end
Method with array as parameter
def max(first, *rest)
result= first
for x in rest do
if (x > result) then
result= x
end
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 (FixNum)
 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
General format of handling exceptions
throw :foo if x==1
end
begin
begin
puts ‘start’
sample # call above method
puts ‘end’
rescue
puts ‘exception found’
end
# - 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
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
end
#code using class
p = Point.new(3,4)
puts "p.x is #{p.x}"
Slide 46
p.x = 44
Another class - Book
class 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}"
end
end
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
@author
end
#method to access class variable author
def author=(new_author)
@author = new_author
end
end
#method to set value of class variable author
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}"
end
end
class ElectronicBook < Book
def initialize(title, author, date, format)
super(title, author, date)
@format = format
end
def to_s
super + " in #{@format}"
end
end
Protection Types –here for methos
class Foo
def method1
end
def method2
end
....
public :method1, method3
protected :method2
private
:method4, method5
end
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
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)
def <(book)
end
return false if book.kind_of(Book) end
title < book.title
end
end
mode = 'a'
File.open('testFile', mode) do |file|
file.print 'cat'
file.puts 'dog'
file.puts 5
end
File I/O
file = File.open('testFile')
while line = file.gets
puts line
end
file.close
File.open('testFile', mode) do |file|
file << 'cat' << "dog\n" << 5 << "\n"
end
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
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
IO.foreach('testFile') {|line| puts line}
a
write-only, append to end of file
puts IO.readlines('testFile')
a+ read/write, start at end of file
array = IO.readlines('testFile')
b
Binary mode, Windows only, combine with above
Threads
require 'net/http'
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
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.com
Fetching slashdot.org
Got www.yahoo.com: OK
Got www.google.com: OK
Got slashdot.org: OK
Note: Thread and HTTP are classes in ruby
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
 Rails Recipes
 Advanced Rails Recipes