Ruby

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Ruby

• A Programmer's First Look

Tim Zappe, October 6th, 2006
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Konnichi wa, Ruby
Ruby is a reflective, object-oriented programming
language. It combines syntax inspired by Perl
with Smalltalk-like object-oriented features, and
also shares some features with Python, Lisp,
Dylan and CLU. Ruby is a single-pass interpreted
language. Its main implementation is free
software distributed under an open-source license.
The language was created by Yukihiro "Matz"
Matsumoto, who started working on Ruby on
February 24, 1993, and released it to the public
in 1995. "Ruby" was named after a colleague's
birthstone. As of September 2006, the latest
stable version is 1.8.5. Ruby 1.9 (with some
major changes) is also in development.
Ruby, a Programmers First Look
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Why Ruby? Why Now?
I think we often become involved with a language
because of a project we can attempt to achieve.
Very seldom are we able to simply build something
in a language without a specific goal in mind. In
my case, Ruby powers a web frame work called
Rails. If it werent for David Heinemeier
Hanssons decision to power Rails with Ruby, I
wouldnt be talking about it today. Even with my
somewhat limited exposure to Ruby, my thanks go
out to both David and Matz for all of their hard
work.
Ruby, a Programmers First Look
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Ruby Features

• object-oriented
• four levels of variable scope global, class,
  instance, and local
• exception handling
• iterators and closures (based on passing blocks
  of code)
• native, Perl-like regular expressions at the
  language level
• operator overloading
• automatic garbage collecting
• highly portable
• cooperative multi-threading on all platforms
  using green threads
• DLL/shared library dynamic loading on most
  platforms
• introspection, reflection and meta-programming
• large standard library
• supports dependency injection
• continuations and generators

Ruby, a Programmers First Look
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Ideals
Ruby is a language of careful balance. Matsumoto
blended parts of his favorite languages (Perl,
Smalltalk, Eiffel, Ada, and Lisp) to form a new
language that balanced functional programming
with imperative programming. He has often said
that he is trying to make Ruby natural, not
simple, in a way that mirrors life.
Ruby, a Programmers First Look
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Growth
Since its public release in 1995, Ruby has drawn
devoted coders worldwide. In 2006, Ruby achieved
mass acceptance. With active user groups formed
in the worlds major cities and Ruby-related
conferences filled to capacity. Ruby-Talk, the
primary mailing list for discussion of the Ruby
language has climbed to an average of 200
messages per day. The TIOBE index, which
measures the growth of programming languages,
ranks Ruby as 13 among programming languages
worldwide. Citing its growth, they predict,
Chances are that Ruby will enter the top 10
within half a year. Much of the growth is
attributed to the popularity of software written
in Ruby, particularly the Ruby on Rails web
framework. Ruby is also totally free. Not only
free of charge, but also free to use, copy,
modify, and distribute.
Current Ratings http//www.tiobe.com/tpci.htm
Ruby, a Programmers First Look
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Everythings an Object
Initially, Matz looked at other languages to find
an ideal syntax. Recalling his search, he said,
I wanted a scripting language that was more
powerful than Perl, and more object-oriented than
Python. In Ruby, everything is an object. Every
bit of information and code can be given their
own properties and actions. Object-oriented
programming calls properties by the name instance
variables and actions are known as methods.
Rubys pure object-oriented approach is most
commonly demonstrated by a bit of code which
applies an action to a number. 5.times print
"We love Ruby -- it's outrageous!" In many
languages, numbers and other primitive types are
not objects. Ruby follows the influence of the
Smalltalk language by giving methods and instance
variables to all of its types. This eases ones
use of Ruby, since rules applying to objects
apply to all of Ruby.
Ruby, a Programmers First Look
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Rubys Flexibility
Ruby is seen as a flexible language, since it
allows its users to freely alter its parts.
Essential parts of Ruby can be removed or
redefined, at will. Existing parts can be added
upon. Ruby tries not to restrict the coder. For
example, addition is performed with the plus ()
operator. But, if youd rather use the readable
word plus, you could add such a method to Rubys
builtin Numeric class. class Numeric def
plus(x) self.(x) end end y 5.plus 6 y
is now equal to 11 Rubys operators are
syntactic sugar for methods. You can redefine
them as well.
Ruby, a Programmers First Look
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Blocks
Rubys block are also seen as a source of great
flexibility. A programmer can attach a closure to
any method, describing how that method should
act. The closure is called a block and has become
one of the most popular features for newcomers to
Ruby from other imperative languages like PHP or
Visual Basic. Blocks are insipired by functional
languages. Matz said, in Ruby closures, I wanted
to respect the Lisp culture. search_engines
wGoogle Yahoo MSN.map do engine
"http//www." engine.downcase ".com"
end In the above code, the block is described
inside the do ... end construct. The map method
applies the block to the provided list of words.
Many other methods in Ruby leave a hole open for
a coder to write their own block to fill in the
details of what that method should do.
Ruby, a Programmers First Look
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Seeing is Believing
While Ruby often uses very limited punctuation
and usually prefers English keywords, some
punctuation is used to decorate Ruby. Ruby needs
no variable declarations. It uses simple naming
conventions to denote the scope of variables.
var could be a local variable. _at_var is an
instance variable. var is a global
variable. These sigils enhance readability by
allowing the programmer to easily identify the
roles of each variable. It also becomes
unnecessary to use a tiresome self. prepended to
every instance member.
Ruby, a Programmers First Look
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More

• Ruby has exception handling features, like Java
  or Python, to make it easy to handle errors.
• Ruby features a true mark-and-sweep garbage
  collector for all Ruby objects. No need to
  maintain reference counts in extension libraries.
  As Matz says, This is better for your health.
• Writing C extensions in Ruby is easier than in
  Perl or Python, with a very elegant API for
  calling Ruby from C. This includes calls for
  embedding Ruby in software, for use as a
  scripting language. A SWIG interface is also
  available.
• Ruby can load extension libraries dynamically if
  an OS allows.
• Ruby features OS independent threading. Thus, for
  all platforms on which Ruby runs, you also have
  multithreading, regardless of if the OS supports
  it or not, even on MS-DOS!
• Ruby is highly portable it is developed mostly
  on GNU/Linux, but works on many types of UNIX,
  Mac OS X, Windows 95/98/Me/NT/2000/XP, DOS, BeOS,
  OS/2, etc.

Ruby, a Programmers First Look
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Write the Language
Many of Rubys parts of speech have visual cues
to help you identify them. Punctuation and
capitalization will help your brain to see bits
of code and feel intense recognition.

• Class Variables
• Blocks
• Block Arguments
• Ranges
• Regular Expressions
• Arrays
• Hashes
• Operators
• Keywords

• Variables
• Numbers
• Strings
• Symbols
• Constants
• Methods
• Class Methods
• Global Variables
• Instance Variables

Ruby, a Programmers First Look
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In the Beginning
Variables
Any plain lowercase word is a variable in Ruby.
Variables may consist of letters, digits, and
underscores
x, y, peterson06, and amazing_ruby_presentation
are examples
Numbers
Integers and floats are both available in Ruby.
In addition, underscores and scientific notation
are available.
42, 10.13, -1234, 12.043e-04, and 53_000_000 are
examples
Strings
Strings are any sort of characters (letters,
digits, punctuation) surrounded by quotes. Both
single and double quotes can be used.
4000, Las Vegas or bust, and Exclusive or
was a the answer! are examples
Ruby, a Programmers First Look
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Specialty Items
Symbols
Symbols are words that look just like variables.
Again, they may contain letters, digits, or
underscores. But they start with a
colon. Symbols are lightweight strings. Usually,
symbols are used in situations where you need a
string but you wont be printing it to the screen.
a, xor, and mister_fancy_pants are examples
Constants
Constants are words like variables, but constants
are capitalized. If variables are the nouns of
Ruby, then think of constants as the proper
nouns. Much like a real proper noun in the
English language, once a Constant is defined it
cannot be changed.
First_Snowfall, The_Empire_State_Building, and
Crested_Butte are examples
Ruby, a Programmers First Look
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Action!
Methods
Methods are like the verbs in Ruby. They are
indicated by a dot. Methods can be strung
together and both question marks and exclamation
points maybe used in method names. Examples
ruby_presentation.attend ruby_presentation.attend.
sleep ruby_presentation.is_interesting? ruby_prese
ntation.speaker( TimZappe ) print See, no dot.
Class Methods
Like the methods described above (also called
instance methods), class methods are usually
attached after variables and constants. Rather
than a dot, a double colon is used.
Presentationnext( Intro to Prolog ) is an
example
Ruby, a Programmers First Look
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All about scope
Global Variables
Variables which begin with a dollar sign are
global.
x, mips, and intel_is_complicated are examples
Instance Variables
Variables that begin with an at symbol are
instance variables and are often used to define
the attributes. For example, you might provide
Ruby with the length of ruby_presentation by
setting the _at_duration variable. Instance
variables are used to define characteristics of a
single object.
_at_duration and _at_coolness are examples
Class Variables
Variables that begin with double at symbols are
class variables and are also used to define
attributes. Instead of defining a single
attribute of a ruby_presentation, it can be used
to define everything that is a Presentation.
_at__at_location and _at__at_heckler are examples
Ruby, a Programmers First Look
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Blocks
Blocks
Any code surrounded by curly braces is a block.
3.times print Beatlejuice is an example
Curly braces can also be traded for do and end.
loop do print Look Ma! print No curly
braces! end
Block Arguments
Block arguments are a set of variables surrounded
by pipe characters and separated by commas. Block
arguments are used at the beginning of a block.
Classmates.each do name, hand print Thanks
for coming, name.capitalize hand.shake end
Ruby, a Programmers First Look
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Ranges and Regular Expressions
Ranges
A range is two values surrounded by parentheses
and separated by an ellipsis (in the form of two
or three dots).
(1..3) is a range, representing the numbers 1
through 3. ('a'..'z') is a range, representing a
lowercase alphabet. (0...5) represents the
numbers 0 through 4.
Regular Expressions
A regular expression (or regexp) is a set of
characters surrounded by slashes.
/ruby/, /0-9/ and /\d3-\d3-\d4/ are
examples.
Ruby, a Programmers First Look
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Arrays and Hashes
Arrays
An array is a list surrounded by square brackets
and separated by commas.
1, 2, 3 is an array of numbers. PHP', Perl',
Python' is an array of strings.
Hashes
A hash is a dictionary surrounded by curly
braces. Dictionaries match words with their
definitions. Ruby does so with arrows made from
an equals sign, followed by a greater-than sign.
sll' gt shift logic left', addi' gt add
immediate is an example.
Ruby, a Programmers First Look
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Operators and Keywords
Operators
Here are the Ruby operators -- know some and look
up others.
! / - ltlt gtgt gt gt lt
lt ltgt ! ! - .. ... not
and or
Keywords
Here are the Ruby keywords -- same catch as above.
alias and BEGIN begin break case
class def defined do else elsif
END end ensure false for if in
module next nil not or redo
rescue retry return self super then
true undef unless until when while
yield
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Code Examples
"Hello, World!" in Ruby puts "Hello, world!"
Sample Class class KaraokeSong lt Song
_at__at_plays 0 def initialize(name, artist,
duration) _at_name name
_at_artist artist _at_duration duration
_at_plays 0 end def play
_at_plays 1 _at__at_plays 1
"This song _at_plays plays. Total _at__at_plays
plays." end end
Greeter Class
Ruby, a Programmers First Look
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Surprises

• Only false and nil evaluate to false
• A float must be defined with a decimal and a
  following digit, 99. is considered a float.
• When calling a character you might find the ASCII
  value being returned. Use either a substring
  operation or a character typecast to obtain the
  character value.

Ruby, a Programmers First Look
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Real Life Examples

• Ruby on Rails
• SketchUp from Google
• RubyGems (Ruby Package Manager)
• Interactive Ruby Shell (irb)
• The Ruby Application Archive lists 1499 projects
• Watir (IE testing application)

Ruby, a Programmers First Look
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Learn Ruby
Output "I love Ruby" say "I love Ruby" puts
say Output "I LOVE RUBY" say'love'
"love" puts say.upcase Output "I love
Ruby" five times 5.times puts say

• http//tryruby.hobix.com/ My Favorite
• http//www.ruby-lang.org/en/documentation/quicksta
  rt/
• http//www.rubycentral.com/book/ Matzs Book
• http//sitekreator.com/satishtalim/index.html
• http//www.ruby-lang.org/ Rubys Home Page
• http//www.ruby-doc.org/
• http//www.ruby-forum.com/
• http//www.rubywizards.com/
• http//raa.ruby-lang.org/
• http//ruby.cenophobie.com/rubycheat.php
  Cheatsheet from today
• http//www.zenspider.com/Languages/Ruby/QuickRef.h
  tml
• http//www.ruby-lang.org/en/documentation/ruby-fro
  m-other-languages/

Ruby, a Programmers First Look