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Ruby (programming language) - Wikipedia, the free encyclopedia
... 2000, the first English language book Programming Ruby was printed, which was ... Ruby has been described as a multi-paradigm programming language: it allows ...
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Ruby programming language - encyclopedia article - Citizendium
Ruby is a general-purpose computer programming language made available as open ... The designers of Ruby (and other programming languages created after Pascal) ...
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{{Infobox programming language|name = Ruby|logo = |paradigm = Multi-paradigm programming language (functional, imperative, logic, object-oriented (class-based))|year = 1995|designer = Yukihiro Matsumoto, [2007 ([Duck typing)|implementations = Ruby, JRuby, [Perl, Lisp programming language, Scheme (programming language), Python (programming language), CLU programming language, Eiffel programming language, Dylan programming language|influenced = Groovy programming language|operating_system = Cross-platform|website = www.ruby-lang.org-->

Ruby is a [reflection (computer science), dynamic programming language, object-oriented programming language. It combines syntax inspired by Perl with Smalltalk-like object-oriented features, and also shares some features with Python (programming language), Lisp (programming language), Dylan (programming language), and CLU (programming language). Ruby is a single-pass interpreted language. Its official implementation is free software written in C (programming language).

History The language was created by Yukihiro Matsumoto, who started working on Ruby on February 24, 1993, and released it to the public in 1995. "Ruby" was named as a gemstone because of a joke within Matsumoto's circle of friends alluding to Perl name An Interview with the Creator of Ruby.

As of March 2007, the latest stable version is 1.8.6. Ruby 1.9 (with some major changes) is also in development. Poor performance of the current Ruby implementation in comparison to other more entrenched programming languages has led to the development of several virtual machines for Ruby. These include JRuby, a port of Ruby to the Java (programming language) platform, IronRuby, an implementation for the .NET Framework produced by Microsoft, and Rubinius, an interpreter modeled after self-hosting Smalltalk virtual machines. The main developers have thrown their weight behind the virtual machine provided by the YARV project, which was merged into the Ruby source tree on 31 December 2006, and will be released as Ruby 2.0.

Philosophy The language's creator has said that Ruby is designed for programmer productivity and fun, following the principles of good user interface design. The Ruby Programming Language by Yukihiro Matsumoto on 2000-06-12 (informit.com) He stresses that systems design needs to emphasize human, rather than computer, needs The Philosophy of Ruby, A Conversation with Yukihiro Matsumoto, Part I by Bill Venners on 2003-09-29 (Artima Developer):

Ruby is said to follow the principle of least surprise (POLS), meaning that the language should behave in such a way as to minimize confusion for experienced users. Matz has said his primary design goal was to make a language that he himself enjoyed using, by minimizing programmer work and possible confusion. He has said he hadn't applied the principle of least surprise to the design of Ruby, The Philosophy of Ruby, A Conversation with Yukihiro Matsumoto, Part I by Bill Venners on 2003-09-29 (Artima Developer) but nevertheless the phrase has come to be closely associated with the Ruby programming language. The phrase has itself been a source of surprise, as novice users may take it to mean that Ruby's behaviors try to closely match behaviors familiar from other languages. In a May 2005 discussion on the comp.lang.ruby newsgroup, Matz attempted to distance Ruby from POLS, explaining that since any design choice will be surprising to someone, he uses a personal standard in evaluating surprise. If that personal standard remains consistent there will be few surprises for those familiar with the standard.

Matz defined it this way in an interview :

Semantics Ruby is object-oriented: every data type is an object, including even classes and types that many other languages designate as primitives (such as integers, booleans, and "nil"). Every function (programming) is a method (programming). Named values (variables) always designate references to objects, not the objects themselves. Ruby supports inheritance (object-oriented programming) with dynamic dispatch, mixins and singleton patterns (belonging to, and defined for, a single instance rather than being defined on the class). Though Ruby does not support multiple inheritance, classes can import module (programming)s as mixins. Procedural syntax is supported, but all methods defined outside of the scope of a particular object are actually methods of the Object class. Since this class is parent to every other class, the changes become visible to all classes and objects.

Ruby has been described as a multi-paradigm programming language: it allows procedural programming (defining functions/variables outside classes makes them part of the root, 'self' Object), with object orientation (everything is an object) or Functional programming (it has anonymous functions, Closure (computer science), and continuations; statements all have values, and functions return the last evaluation). It has support for Introspection (computer science), Reflection (computer science) and metaprogramming, as well as support for interpreter-basedGreen threads Thread (computer science)s. Ruby features Type system, and supports Polymorphism in object-oriented programming.

According to the Ruby FAQ Ruby FAQ, "If you like Perl, you will like Ruby and be right at home with its syntax. If you like Smalltalk, you will like Ruby and be right at home with its semantics. If you like Python (programming language), you may or may not be put off by the huge difference in design philosophy between Python and Ruby/Perl." How Does Ruby Compare With Python? (FAQ)

Features

• object-oriented
• four levels of variable scope: Global variable, class, instance, and local
• exception handling
• iterators and closure (computer science) (based on passing blocks of code)
• native, Perl-like regular expressions at the language level
• operator overloading
• garbage collection (computer science)
• highly porting
• cooperative multi-threading on all platforms using Green threads
• Dynamic-Link Library/Library (computer science) dynamic loading on most platforms
• Introspection (computer science), Reflection (computer science) and metaprogramming
• large standard library
• supports dependency injection
• continuations and Generator (computer science) (examples in RubyGarden: continuations and generators)

Ruby currently lacks full support for Unicode, though it has partial support for UTF-8.

Interaction The Ruby official distribution also includes "irb", an interactive command-line interpreter which can be used to test code quickly. The following code fragment represents a sample session using irb:

$ irbirb(main):001:0> puts "Hello, World"Hello, World=> nilirb(main):002:0> 1+2=> 3

Syntax The syntax of Ruby is broadly similar to Perl and Python. Class and method definitions are signaled by keywords. In contrast to Perl, variables are not obligatorily prefixed with a sigil (computer programming). When used, the sigil changes the semantics of scope of the variable. The most striking difference from C and Perl is that keywords are typically used to define logical code blocks, without braces (i.e., pair of { and }). Line breaks are significant and taken as the end of a statement; a semicolon may be equivalently used. Unlike Python, indentation is not significant.

One of the differences of Ruby compared to Python and Perl is that Ruby keeps all of its instance variables completely private to the class and only exposes them through accessor methods (attr_writer, attr_reader, etc). Unlike the "getter" and "setter" methods of other languages like C++ or Java, accessor methods in Ruby can be written with a single line of code. As invocation of these methods does not require the use of parentheses, it is trivial to change an instance variable into a full function, without modifying a single line of code or having to do any refactoring achieving similar functionality to C# and VB.NET property members. Python's property descriptors are similar, but come with a tradeoff in the development process. If one begins in Python by using a publicly exposed instance variable and later changes the implementation to use a private instance variable exposed through a property descriptor, code internal to the class may need to be adjusted to use the private variable rather than the public property. Ruby removes this design decision by forcing all instance variables to be private, but also provides a simple way to declare set and get methods. This is in keeping with the idea that in Ruby, one never directly accesses the internal members of a class from outside of it. Rather one passes a message to the class and receives a response.

See the #Examples section for samples of code demonstrating Ruby syntax.

"Gotchas" Language comparison Some features that differ notably from languages such as C (programming language) or Perl:

• Names that begin with a capital letter are treated as constants, so local variables should begin with a lowercase letter.
• The symbols $ @ are not Sigil (computer programming) as in Perl, but rather function as scope resolution operators.
• To denote floating point numbers, one must follow with a zero digit (99.0) or an explicit conversion (99.to_f). It is insufficient to append a dot (99.) because numbers are susceptible to method syntax.
• Boolean datatype evaluation of non-boolean data is strict: 0, "" and are all evaluated to true. In C, the expression 0 ? 1 : 0 evaluates to 0 (i.e. false). In Ruby, however, it yields 1, as all numbers evaluate to true; only nil and false evaluate to false. A corollary to this rule is that Ruby methods by convention — for example, regular expression searches — return numbers, strings, lists, or other non-false values on success, but nil on failure (e.g., mismatch). This convention is also used in Smalltalk, where only the special objects true and false can be used in a boolean expression.
• Versions prior to 1.9 lack a character data type (compare to C, which provides type char for characters). This may cause surprises when slicing strings: "abc" yields 97 (an integer, representing the ASCII code of the first character in the string); to obtain "a" use "abc" (a substring of length 1) or "abc".chr.
• The notation "statement until expression", despite the English-language implication that the statement would be executed at least once, which follows the precedent used in other languages' equivalent statements (e.g. "do { statement } while (not(expression));" in C/C++/...), actually never runs the statement if the expression is already true.
• Because constants are references to objects, changing what a constant refers to generates a warning, but modifying the object itself does not. For example, if Greeting = "Hello" then Greeting 'wet', :fire => 'hot'}puts hash # Prints: hot
  
  hash.each_pair do |key, value| # Or: hash.each do |key, value|puts "#{key} is #{value}" end
  
  
• Prints: water is wet
• fire is hot


hash.delete_if {|key, value| key == :water} # Deletes :water => 'wet'

Blocks and iterators The two syntaxes for creating a code block:

{ puts "Hello, World!" } # Note the { braces }

do puts "Hello, World!" end

Parameter-passing a block to be a Closure (computer science):


• In an object instance variable (denoted with '@'), remember a block.
def remember(&a_block)@block = a_block end


• Invoke the above method, giving it a block that takes a name.
remember {|name| puts "Hello, #{name}!"}


• When the time is right (for the object) -- call the closure!
@block.call("Jon")
• => "Hello, Jon!"


Returning closures from a method:

def create_set_and_get(initial_value=0) # Note the default value of 0closure_value = initial_value return Proc.new {|x| closure_value = x}, Proc.new { closure_value } end

setter, getter = create_set_and_get # ie. returns two valuessetter.call(21)getter.call # => 21

Yielding the flow of program control to a block which was provided at calling time:

def use_helloyield "hello" end


• Invoke the above method, passing it a block.
use_hello {|string| puts string} # => 'hello'

Iterating over enumerations and arrays using blocks:

array = 'hi', 3.14array.each {|item| puts item}
• => 1
• => hi
• => 3.14


(3..6).each {|num| puts num}
• => 3
• => 4
• => 5
• => 6


A method such as inject() can accept both a parameter and a block. Inject iterates over each member of a list, performing some function on while retaining an aggregate. This is analogous to the foldl function in functional programming languages. For example:

.inject(10) {|sum, element| sum + element} # => 19

On the first pass, the block receives 10 (the argument to inject) as sum, and 1 (the first element of the array) as element, This returns 11. 11 then becomes sum on the next pass, which is added to 3 to get 14. 14 is then added to 5, to finally return 19.

Blocks work with many built-in methods:

File.open('file.txt', 'w') do |file| # 'w' denotes "write mode".file.puts 'Wrote some text.' end # File is automatically closed here

File.readlines('file.txt').each do |line|puts line end
• => Wrote some text.


Using an enumeration and a block to square the numbers 1 to 10:

(1..10).collect {|x| x*x} # => 4, 9, 16, 25, 36, 49, 64, 81, 100

Classes The following code defines a class named Person. In addition to 'initialize', the usual constructor to create new objects, it has two methods: one to override the comparison operator (so Array#sort can sort by age) and the other to override the to_s method (so Kernel#puts can format its output). Here, "attr_reader" is an example of metaprogramming in Ruby: "attr_accessor" defines getter and setter methods of instance variables, "attr_reader" only getter methods. Also, the last evaluated statement in a method is its return value, allowing the omission of an explicit 'return'.

class Persondef initialize(name, age) @name, @age = name, age end def (person) # Comparison operator for sorting @age person.age end def to_s "#@name (#@age)" end attr_reader :name, :age end

group = [Person.new("Jon", 20), Person.new("Marcus", 63), Person.new("Ash", 16) ]

puts group.sort.reverse

The above prints three names in reverse age order:Marcus (63)Jon (20)Ash (16)

Exceptions An exception is raised with a raise call:raise

An optional message can be added to the exception:raise "This is a message"

You can also specify which type of exception you want to raise:raise ArgumentError, "Illegal arguments!"

Exceptions are handled by the rescue clause. Such a clause can catch exceptions that inherit from StandardError:

begin
• Do something
rescue
• Handle exception
end

Note that it is a common mistake to attempt to catch all exceptions with a simple rescue clause. To catch all exceptions one must write:

begin
• Do something
rescue Exception # don't write just rescue -- this only catches StandardError, a subclass of Exception
• Handle exception
end

Or catch particular exceptions:

begin
• ...
rescue RuntimeError
• handling
end

It is also possible to specify that the exception object be made available to the handler clause:

begin
• ...
rescue RuntimeError => e
• handling, possibly involving e, such as "print e.to_s"
end

Alternatively, the most recent exception is stored in the magic global $!.

You can also catch several exceptions:begin
• ...
rescue RuntimeError, Timeout::Error => e
• handling, possibly involving e
end

Or catch an array of exceptions:array_of_exceptions = Timeout::Errorbegin
• ...
rescue *array_of_exceptions => e
• handling, possibly involving e
end

More examples More sample Ruby code is available as algorithms in the following articles:
• Exponentiating by squaring
• Associative array#Ruby
• Trabb Pardo-Knuth algorithm


Implementations Ruby has two main implementations: The official Ruby interpreter (computer software) (often referred to as the MRI or Matz's Ruby Interpreter), which is the most widely used, and JRuby, a Java (programming language)-based implementation.

There are other less known implementations such as IronRuby (Development stage#Alpha sources available on August 31st, 2007), Rubinius, Ruby.NET, XRuby and YARV. YARV is sometimes referred as the next official Ruby engine.

Operating systems Ruby is available for the following operating systems:


• Acorn Computers Ltd RISC OS
• Amiga
• BeOS
• DOS
• Linux
• Mac OS X
• Microsoft Windows 95/98/2000/2003/NT/XP/Vista
• Microsoft Windows CE
• MorphOS
• OS/2
• OpenVMS
• Syllable (operating system)
• Symbian os
• Blue Gene/L compute node kernel
• Most flavors of Unix


Other ports may also exist.

Licensing terms The Ruby interpreter and libraries are distributed disjointedly (dual licensed) under the Free software and open source licenses GNU General Public License and Ruby License Ruby License (ruby-lang.org).

Criticism The current 1.8 version of Ruby main interpreter has some limitations. On 1 January 2007, work had begun for version 1.9 which is planned to produce Ruby 2.0 later in 2007 or in 2008. The problems of the current stable version include:
• As a dynamic scripting language, Ruby's speed is much less than that of other languages, including scripting languages such as Perl, PHP, or Python (programming language) . However, the next version of Ruby will include a new, faster interpreter, YARV.
• The Ruby threading model uses green threads , and its model has some inherent limitations that render it difficult to use or unsafe for some user-case scenarios. - however, version 2.0 of Ruby will not implement green threads,
• Ruby does not yet have native support for Unicode or multibyte strings (expected in version 2.0).


Some problems that may not be solved in version 2.0 include:
• Ruby still lacks a specification, the current reference specification being the de facto C implementation. .


Repositories and libraries The Ruby Application Archive (RAA), as well as RubyForge, serve as repositories for a wide range of Ruby applications and libraries, containing more than two thousand items. Although the number of applications available does not match the volume of material available in the Perl or Python (programming language) community, there are a wide range of tools and utilities which serve to foster further development in the language.

RubyGems has become the standard package manager for Ruby libraries. It is very similar in purpose to Perl's CPAN, although its usage is more like apt-get.

References

See also
• Duck typing
• RubyGems (a Ruby package manager)
• Nitro_(web_framework) (a Ruby web application framework)
• Ruby on Rails (a Ruby web application framework)
• Ruby Application Archive
• Interactive Ruby Shell
• IronRuby, a CIL-compiled version of Ruby for .NET Framework
• Comparison of programming languages
• Watir
• JRuby (a pure Java implementation of the Ruby interpreter)
• RadRails Ruby/Rails IDE (based on Eclipse (software))
• Rinda (parallel programming extension for Ruby)
• NetBeans (Add to NetBeans IDE tools for programming in the Ruby language)


External links
• Ruby language home page
• Ruby documentation site
• Browser based Ruby shell
• Why's (Poignant) Guide to Ruby - An online Ruby book for beginning coders which reads like an illustrated novel.
• Ruby programming language at the Open Directory Project
• comp.lang.ruby Usenet group
• Ruby implementations shootout
• Ruby.on-page.net — the simplest Ruby manual
• Eclipse Dynamic Languages Toolkit for Ruby, IDE with intellisense features like type inference and smart code completion.
• NetBeans Ruby support Code Completion, Full Semantic Highlighting, Debugging, Refactoring, Rails Support, Documenation
• Get started using NetBeans Ruby Support in the IDE
• Nitro: Web applications made easy
• Creating a Ruby Weblog in 10 Minutes
• Ruby on Rails plugin directory and job board
• Some interesting articles on using Ruby
• Full Ruby on Rails Tutorial - A complete beginners intro to Ruby on Rails
• Ruby User Guide Mirror
• Find Ruby with Google Code Search
• Ruby From Other Languages






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