Sam Ruby has a cool slideshow that outline the differences.

In the interest of bringing this information inline for easier reference, and in case the link goes dead in the abstract future, here's an overview of Sam's slides. The slideshow is less overwhelming to review, but having it all laid out in a list like this is also helpful.

Ruby 1.9 - Major Features

• Performance
• Threads/Fibers
• Encoding/Unicode
• gems is (mostly) built-in now
• if statements do not introduce scope in Ruby.

What's changed?

Single character strings.

Ruby 1.9

irb(main):001:0> ?c=> "c"

Ruby 1.8.6

irb(main):001:0> ?c=> 99

String index.

Ruby 1.9

irb(main):001:0> "cat"[1]=> "a"

Ruby 1.8.6

irb(main):001:0> "cat"[1]=> 97

{"a","b"} No Longer Supported

Ruby 1.9

irb(main):002:0> {1,2}SyntaxError: (irb):2: syntax error, unexpected ',', expecting tASSOC

Ruby 1.8.6

irb(main):001:0> {1,2}=> {1=>2}

Action: Convert to {1 => 2}

Array.to_s Now Contains Punctuation

Ruby 1.9

irb(main):001:0> [1,2,3].to_s=> "[1, 2, 3]"

Ruby 1.8.6

irb(main):001:0> [1,2,3].to_s=> "123"

Action: Use .join instead

Colon No Longer Valid In When Statements

Ruby 1.9

irb(main):001:0> case 'a'; when /\w/: puts 'word'; endSyntaxError: (irb):1: syntax error, unexpected ':',expecting keyword_then or ',' or ';' or '\n'

Ruby 1.8.6

irb(main):001:0> case 'a'; when /\w/: puts 'word'; endword

Action: Use semicolon, then, or newline

Block Variables Now Shadow Local Variables

Ruby 1.9

irb(main):001:0> i=0; [1,2,3].each {|i|}; i=> 0irb(main):002:0> i=0; for i in [1,2,3]; end; i=> 3

Ruby 1.8.6

irb(main):001:0> i=0; [1,2,3].each {|i|}; i=> 3

Hash.index Deprecated

Ruby 1.9

irb(main):001:0> {1=>2}.index(2)(irb):18: warning: Hash#index is deprecated; use Hash#key=> 1irb(main):002:0> {1=>2}.key(2)=> 1

Ruby 1.8.6

irb(main):001:0> {1=>2}.index(2)=> 1

Action: Use Hash.key

Fixnum.to_sym Now Gone

Ruby 1.9

irb(main):001:0> 5.to_symNoMethodError: undefined method 'to_sym' for 5:Fixnum

Ruby 1.8.6

irb(main):001:0> 5.to_sym=> nil

(Cont'd) Ruby 1.9

# Find an argument value by name or index.def [](index)  lookup(index.to_sym)end

svn.ruby-lang.org/repos/ruby/trunk/lib/rake.rb

Hash Keys Now Unordered

Ruby 1.9

irb(main):001:0> {:a=>"a", :c=>"c", :b=>"b"}=> {:a=>"a", :c=>"c", :b=>"b"}

Ruby 1.8.6

irb(main):001:0> {:a=>"a", :c=>"c", :b=>"b"}=> {:a=>"a", :b=>"b", :c=>"c"}

Order is insertion order

Stricter Unicode Regular Expressions

Ruby 1.9

irb(main):001:0> /\x80/uSyntaxError: (irb):2: invalid multibyte escape: /\x80/

Ruby 1.8.6

irb(main):001:0> /\x80/u=> /\x80/u

tr and Regexp Now Understand Unicode

Ruby 1.9

unicode(string).tr(CP1252_DIFFERENCES, UNICODE_EQUIVALENT).  gsub(INVALID_XML_CHAR, REPLACEMENT_CHAR).  gsub(XML_PREDEFINED) {|c| PREDEFINED[c.ord]}

pack and unpack

Ruby 1.8.6

def xchr(escape=true)  n = XChar::CP1252[self] || self  case n when *XChar::VALID    XChar::PREDEFINED[n] or       (n>128 ? n.chr : (escape ? "&##{n};" : [n].pack('U*')))  else    Builder::XChar::REPLACEMENT_CHAR  endendunpack('U*').map {|n| n.xchr(escape)}.join

BasicObject More Brutal Than BlankSlate

Ruby 1.9

irb(main):001:0> class C < BasicObject; def f; Math::PI; end; end; C.new.fNameError: uninitialized constant C::Math

Ruby 1.8.6

irb(main):001:0> require 'blankslate'=> trueirb(main):002:0> class C < BlankSlate; def f; Math::PI; end; end; C.new.f=> 3.14159265358979

Action: Use ::Math::PI

irb(main):002:0> class C < SimpleDelegator; end=> nilirb(main):003:0> C.new('').class=> String

irb(main):002:0> class C < SimpleDelegator; end=> nilirb(main):003:0> C.new('').class=> Cirb(main):004:0>

irb(main):004:1> $KCODE = 'UTF8'(irb):4: warning: variable $KCODE is no longer effective; ignored=> "UTF8"

irb(main):001:0> $KCODE = 'UTF8'=> "UTF8"

irb(main):001:0> {}.methods.sort.last=> :zip

irb(main):001:0> {}.methods.sort.last=> "zip"

# coding: utf-8

# -*- encoding: utf-8 -*-

#!/usr/local/rubybook/bin/ruby# encoding: utf-8

{a: b}redirect_to action: show

{:a => b}redirect_to :action => show

[1,2].each {|value; t| t=value*value}

[1,2].inject(:+)

[1,2].inject {|a,b| a+b}

short_enum = [1, 2, 3].to_enumlong_enum = ('a'..'z').to_enumloop do  puts "#{short_enum.next} #{long_enum.next}"end

e = [1,2,3].each

p = -> a,b,c {a+b+c}puts p.(1,2,3)puts p[1,2,3]

p = lambda {|a,b,c| a+b+c}puts p.call(1,2,3)

Complex(3,4) == 3 + 4.im

irb(main):001:0> 1.2-1.1=> 0.0999999999999999

/\p{Space}/

/[:space:]/

def foo(first, *middle, last)(->a, *b, c {p a-c}).(*5.downto(1))

f = Fiber.new do  a,b = 0,1  Fiber.yield a  Fiber.yield b  loop do    a,b = b,a+b    Fiber.yield b  endend10.times {puts f.resume}

match =   while line = gets     next if line =~ /^#/     break line if line.find('ruby')   end

def toggle  def toggle    "subsequent times"  end  "first time"end