What is the difference between Ruby 1.8 and Ruby 1.9 - ruby

Question

I'm not clear on the differences between the "current" version of Ruby (1.8) and the "new" version (1.9). Is there an "easy" or a "simple" explanation of the differences and why it is so different?

Answer 1

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Colon No Longer Valid In When Statements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
Delegation Changes
Ruby 1.9
irb(main):002:0> class C < SimpleDelegator; end
=> nil
irb(main):003:0> C.new('').class
=> String
Ruby 1.8.6
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!

Answer 2

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

Answer 3

Many now recommend The Ruby Programming Language over the Pickaxe - more to the point, it has all the details of the 1.8/1.9 differences.

Answer 4

Some more changes:
Returning a splat singleton array:
def function
return *[1]
end
a=function
ruby 1.9 : [1]
ruby 1.8 : 1
array arguments
def function(array)
array.each { |v| p v }
end
function "1"
ruby 1.8: "1"
ruby 1.9: undefined method `each' for "1":String