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Colon No Longer Valid In When Statements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'; end
SyntaxError: (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'; end
word

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
=> 0
irb(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
=> 1
irb(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_sym
NoMethodError: 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/u
SyntaxError: (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
  end
end
unpack('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.f
NameError: uninitialized constant C::Math

Ruby 1.8.6

irb(main):001:0> require 'blankslate'
=> true
irb(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
=> nil
irb(main):003:0> C.new('').class
=> String

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

Defect 17700

Use of $KCODE Produces Warnings

Ruby 1.9

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

Ruby 1.8.6

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

instance_methods Now an Array of Symbols

Ruby 1.9

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

Ruby 1.8.6

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

Action: Replace instance_methods.include? with method_defined?

Source File Encoding

Basic

# coding: utf-8

Emacs

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

Shebang

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

Real Threading

• Race Conditions
• Implicit Ordering Assumptions
• Test Code

What's New?

Alternate Syntax for Symbol as Hash Keys

Ruby 1.9

{a: b}

redirect_to action: show

Ruby 1.8.6

{:a => b}

redirect_to :action => show

Block Local Variables

Ruby 1.9

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

Inject Methods

Ruby 1.9

[1,2].inject(:+)

Ruby 1.8.6

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

to_enum

Ruby 1.9

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

No block? Enum!

Ruby 1.9

e = [1,2,3].each

Lambda Shorthand

Ruby 1.9

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

Ruby 1.8.6

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

Complex Numbers

Ruby 1.9

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

Decimal Is Still Not The Default

Ruby 1.9

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

Regex “Properties”

Ruby 1.9

/\p{Space}/

Ruby 1.8.6

/[:space:]/

Splat in Middle

Ruby 1.9

def foo(first, *middle, last)

(->a, *b, c {p a-c}).(*5.downto(1))

Fibers

Ruby 1.9

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

Break Values

Ruby 1.9

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

“Nested” Methods

Ruby 1.9

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

HTH!

One huge difference would be the move from Matz's interpreter to YARV, a bytecode virtual machine that helps significantly with performance.