Learning Ruby

Mike FitzgeraldOSCON 2007

July 23, 2007 2

Thank you“Matz”Matsumoto Yukihiro

July 23, 2007 3

Today’s schedule

8:30–9:40 AM: Instruction (70 minutes)

9:40–9:50 AM: Break (10 minutes)

9:50–11:00 AM: Instruction (70 minutes)

11:00–11:10 AM: Break (10 minutes)

11:10 AM–12 noon: Instruction (50 minutes)

July 23, 2007 4

Ruby history

• Matz had wanted to create his own language since high school

• Development started in 1993• First release was in 1995 (same

time as Java)• Emerged in the West around 2000• Ruby on Rails brought it wide

attention in 2004

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What is Ruby?

• Object-oriented scripting language• Open source• Mature and stable• Complex language with a simple

syntax

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What is Ruby? continued

• Interpreted rather than compiled• Core written in C • Can write C extensions, too• Borrows ideas from Lisp, Perl,

Smalltalk, etc.

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Numbers

• Numbers are not primitives but objects

• Most operators are methods• No declarations or static types• Dynamic typing• Duck typing, a kind of dynamic

typing

July 23, 2007 8

Numbers continued

• No increment (++) or decrement (--) operators in Ruby

• Abbreviated assignment operators, such as +=, -=, *=, etc.

• Underscores ignored (1_000_000)• Ranges: 1..10 (inclusive) or 2...5

(exclusive)• Math module: Math.sqrt, Math.sin, etc.

July 23, 2007 9

$ which ruby # [Li|U]nix only

/usr/local/bin/ruby

$ ruby --version

ruby 1.8.6 (2007-03-13 patchlevel 0) [powerpc-darwin8.9.0]

$ irb # Interactive Ruby

irb(main):001:0>

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Running a Ruby program(Windows, [Li|U]nix])

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$ ruby hello.rb

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“Hello, world”or

Printing a string to standard output

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print "Good morning!"

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puts "Hello, Portland."

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Comments

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# say hello

puts "Hello!"

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puts "Hello!" # say hello

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Block comments

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=begin

Say hello to all the

nice people out there.

=end

puts "Hello!"

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Concatenating strings

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print "I like ", "trees."

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puts "I like " + "sushi."

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puts "I like " << "Powell’s."

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Shebang ([Li|U]nix)

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#!/usr/bin/env ruby

puts "Hello!"

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$ chmod 755 hello.rb

$ hello.rb

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Inserting shell output using backticks

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puts "Running " + `ruby -v`

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Issuing a system (shell) command

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system "echo 'Hello, Matz!'"

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Evaluating an expression

July 23, 2007 32

eval "puts 'Hi there.'"

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$ ruby -e "puts 'Hi there.'"

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Multiplicity

July 23, 2007 35

puts "Go!" * 3

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3.times { print "Go! " }

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Variables

• Local variable: start with lowercase letter or _

• Instance variables in class: @name• Class variables: @@times• Global variables: $amount

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hello = "Hello, universe!"

puts hello

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good = "Guten "

day = "Tag"

puts good + day

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x = 9

y = 18

puts x + y

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Parallel assignment

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x, y = 37, 63

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a, b, c = "15", "tons", "200.0"

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c, d = 15, "tons"

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Symbols

• Special object in Ruby• Placeholders for identifiers and

strings• Begin with colon (:)• Not directly created through

assignment• Efficient: Only one copy held in a

single memory address

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name = "Javert"

name.to_sym # => :Javert

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:Javert.id2name # => "Javert"

name == :Javert.id2name # true

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Expression substitution

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x, y = 37, 63

puts #{x + y}

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name = "guy"

puts "Hi, #{name}!"

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Retrieving command-line arguments

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#!/usr/bin/env ruby

puts "Hello, #{ARGV[0]}!"

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$ arg.rb everybody

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Formatting output

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sprintf( "Hello, %s!", "Tim" )

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printf( "Hello, %s!", "Sam" )

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hi = "Hello, %s"

puts hi % "people!"

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"%s, %s!" % [ "Hello", "Tim" ]

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Getting input from the prompt

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#!/usr/bin/env ruby

print "Say hello to..."

hi = gets

puts "Hello, " + hi

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$ get.rb

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Define and call a method

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def hello

puts "Hello"

end

hello

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Aliasing a method

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alias hi hello

hi

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Undefining a method

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undef hello

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Defining a method with an argument

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def hello( who )

puts "Hello " + who + "."

end

hello "Yuri"

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def repeat( word, times )

puts word * times

end

repeat "Go! ", 3

July 23, 2007 71

Return a value explicitly

July 23, 2007 72

def hello

return "Hello."

end

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Defining a method with a defaultvalue for an argument

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def hello( who="Schlomo" )

puts "Hello " + who + "."

end

hello

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Defining a method with a variable

number of arguments

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def hello( *args )

puts args.size

end

July 23, 2007 77

def two_plus( one, two, *args ) length = args.size label = length == 1 ? " variable argument" : " variable arguments"

num = length.to_s + label + " (" + args.inspect + ")"

numend

puts two_plus( 1, 2 )

July 23, 2007 78

Yielding a block

July 23, 2007 79

def hello

yield

end

hello { puts "Hello, Matz." }

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Defining and calling a procedure (proc)

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proc = lambda { puts "Hello!" }

proc.call

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Calling the each method

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["Hi","Mel"].each {|e| print e}

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XML

July 23, 2007 85

<hello>there!</hello>

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#!/usr/bin/env ruby

require "rexml/document"

file = File.new( "hello.xml" )

doc = REXML::Document.new file

puts doc.to_s

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Conditional statements

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if

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x, y = 45, 32

if x > y then

puts "x is greater than y"

end

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if hi == false: puts "Goodbye" end

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if hi == true

puts "Hi"

end

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if !hi == false

puts "Hello!"

end

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Multiple tests

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if ruby=="nifty" && programming=="fun"

puts "Keep programming!"

end

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if ruby=="nifty" and programming=="fun"

puts "Keep programming!"

end

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if a == 10 || b == 27

print a + b

end

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if a == 10 or b == 27

print a + b

end

July 23, 2007 98

Statement modifier for if

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puts "x is less than y" if x < y

July 23, 2007 100

Using else

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if x >= y

puts "x greater than or equal to y"

else

puts "x not greater than or equal to y"

end

July 23, 2007 102

Using elseif

July 23, 2007 103

if x == y puts "x equals y"elsif x != y puts "x is not equal to y"elsif x > y puts "x is greater than y"elsif x < y puts "x is less than y"elsif x >= y puts "x is greater than or equal to y"elsif x <= y puts "x is less than or equal to y"else puts "Arrrrgh!"end

July 23, 2007 104

Using the colon

July 23, 2007 105

lang = "de"

if lang == "en": print "dog"

elsif lang == "es": print "perro"

elsif lang == "fr": print "chien"

elsif lang == "de": print "Hund"

else puts "dog"

end

July 23, 2007 106

The negated form of if: unless

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if lang == "de"

dog = "Hund"

else

dog = "dog"

end

July 23, 2007 108

unless lang == "de"

dog = "dog"

else

dog = "Hund"

end

July 23, 2007 109

Statement modifier for unless

July 23, 2007 110

puts num += 1 unless num > 88

July 23, 2007 111

while

July 23, 2007 112

i = 0breeds = [ "quarter", "arabian", "appaloosa", "paint" ]

puts breeds.size # => 4temp = []

while i < breeds.size do temp << breeds[i].capitalize i +=1end

July 23, 2007 113

temp.sort! # => ["Appaloosa", "Arabian", "Paint", "Quarter"]

breeds.replace( temp )

p breeds # => ["Appaloosa", "Arabian", "Paint", "Quarter"]

July 23, 2007 114

temp = 98.3

begin print "Your temperature is " + temp.to_s + " Fahrenheit. "

puts "I think you're okay." temp += 0.1end while temp < 98.6

July 23, 2007 115

while i < breeds.size

temp << breeds[i].capitalize

break if temp[i] == "Arabian"

i +=1

end

p temp # => ["Quarter", "Arabian"]

July 23, 2007 116

Statement modifier for while

July 23, 2007 117

cash = 100_000.00

sum = 0

cash += 1.00, sum while cash < 1_000_000.00 # _ ignored

July 23, 2007 118

The negated form of while: until

July 23, 2007 119

weight = 150

while weight < 200 do

puts "Weight: " + weight.to_s

weight += 5

end

July 23, 2007 120

weight = 150

until weight == 200 do

puts "Weight: " + weight.to_s

weight += 5

end

July 23, 2007 121

weight = 150

begin

puts "Weight: " + weight.to_s

weight += 5

end until weight == 200

July 23, 2007 122

Statement modifier for until

July 23, 2007 123

puts age += 1 until age > 28

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case

July 23, 2007 125

lang = :de

dog = case lang when :en: "dog" when :es: "perro" when :fr: "chien" when :de: "Hund" else "dog"end

July 23, 2007 126

With ranges

July 23, 2007 127

scale = 8case scale when 0: puts "lowest" when 1..3: puts "medium-low" when 4..5: puts "medium" when 6..7: puts "medium-high" when 8..9: puts "high" when 10: puts "highest" else puts "off scale"end

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Ternary operator

July 23, 2007 129

def two_plus( one, two, *args ) length = args.size label = length == 1 ? " variable argument" : " variable arguments"

num = length.to_s + label + " (" + args.inspect + ")"

numend

puts two_plus( 1, 2 )

July 23, 2007 130

for loop

July 23, 2007 131

for i in 1..10 do print i, " " end

# => 1 2 3 4 5 6 7 8 9 10

July 23, 2007 132

upto method

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1.upto(10) { |i| print i, " " }

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downto mehtod

July 23, 2007 135

10.downto(1) {|i| print i," " }

July 23, 2007 136

Classes

• Almost everything is an object• Instance variables and methods• Class variables and methods• Single inheritance only• Classes are open, even built-in

classes

July 23, 2007 137

class Hello

def initialize( name )

@name = name

end

def hi

puts "Hello, "+@name+"!"

end

end

July 23, 2007 138

hello = Hello.new( "Matz!" )

hello.hi

July 23, 2007 139

Modules

• Module hold method definitions, etc.• You cannot instantiate modules• But you can include (mixin) modules• Methods, etc., are implemented in

modules but never available until mixed in

• Bridge between single and multiple inheritance