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Ruby (programming language)

 

Ruby (programming language)

Ruby
Paradigm(s) multi-paradigm: object-oriented, imperative, functional, reflective
Designed by Yukihiro Matsumoto
Developer Yukihiro Matsumoto, et al.
Appeared in 1995 (1995)
Stable release 2.1.5 / November 13, 2014 (2014-11-13)[1]
Typing discipline duck, dynamic
Scope lexical, sometimes dynamic
Major implementations Ruby MRI, YARV, Rubinius, MagLev, JRuby, MacRuby, RubyMotion, HotRuby, IronRuby, Mruby
Influenced by Ada,[2] C++,[2] CLU,[3] Dylan,[3] Eiffel,[2] Lua, Lisp,[3] Perl,[3] Python,[3] Smalltalk[3]
Influenced Clojure, D,[4] Elixir, Falcon, Fancy,[5] Groovy, Ioke,[6] Julia,[7]Mirah, Nu,[8] potion, Reia, Swift[9]
OS Cross-platform
License Ruby, GPLv2 or 2-clause BSD license[10][11][12]
Filename extension(s) .rb, .rbw
Website .org.ruby-langwww
  • Ruby Programming at Wikibooks

Ruby is a dynamic, reflective, object-oriented, general-purpose programming language. It was designed and developed in the mid-1990s by Yukihiro "Matz" Matsumoto in Japan.

According to its authors, Ruby was influenced by Perl, Smalltalk, Eiffel, Ada, and Lisp.[13] It supports multiple programming paradigms, including functional, object-oriented, and imperative. It also has a dynamic type system and automatic memory management.

Contents

  • History 1
    • Early concept 1.1
    • The name "Ruby" 1.2
    • First publication 1.3
    • Early releases 1.4
    • Ruby 1.8 1.5
    • Ruby 1.9 1.6
    • Ruby 2.0 1.7
    • Ruby 2.1 1.8
  • Philosophy 2
  • Features 3
  • Semantics 4
  • Syntax 5
  • Differences from other languages 6
  • Interaction 7
  • Examples 8
    • Strings 8.1
    • Collections 8.2
    • Blocks and iterators 8.3
    • Classes 8.4
      • Open classes 8.4.1
    • Exceptions 8.5
    • Metaprogramming 8.6
    • More examples 8.7
  • Implementations 9
    • Matz's Ruby Interpreter 9.1
    • Alternate implementations 9.2
    • Platform support 9.3
  • Repositories and libraries 10
  • See also 11
  • References 12
  • Further reading 13
  • External links 14

History

Early concept

Ruby was conceived on February 24, 1993. In a 1999 post to the ruby-talk mailing list, Ruby author Yukihiro Matsumoto describes some of his early ideas about the language:[14]

I was talking with my colleague about the possibility of an object-oriented scripting language. I knew Perl (Perl4, not Perl5), but I didn't like it really, because it had the smell of a toy language (it still has). The object-oriented language seemed very promising. I knew Python then. But I didn't like it, because I didn't think it was a true object-oriented language — OO features appeared to be add-on to the language. As a language maniac and OO fan for 15 years, I really wanted a genuine object-oriented, easy-to-use scripting language. I looked for but couldn't find one. So I decided to make it.

Matsumoto describes the design of Ruby as being like a simple Lisp language at its core, with an object system like that of Smalltalk, blocks inspired by higher-order functions, and practical utility like that of Perl.[15]

The name "Ruby"

The name "Ruby" originated during an online chat session between Matsumoto and Keiju Ishitsuka on February 24, 1993, before any code had been written for the language.[16] Initially two names were proposed: "Coral" and "Ruby". Matsumoto chose the latter in a later e-mail to Ishitsuka.[17] Matsumoto later noted a factor in choosing the name "Ruby" – it was the birthstone of one of his colleagues.[18][19]

First publication

The first public release of Ruby 0.95 was announced on Japanese domestic newsgroups on December 21, 1995.[20][21] Subsequently three more versions of Ruby were released in two days.[16] The release coincided with the launch of the Japanese-language ruby-list mailing list, which was the first mailing list for the new language.

Already present at this stage of development were many of the features familiar in later releases of Ruby, including object-oriented design, classes with inheritance, mixins, iterators, closures, exception handling and garbage collection.[22]

Early releases

Following the release of Ruby 0.95 in 1995, several stable versions of Ruby were released in the following years:

  • Ruby 1.0: December 25, 1996[16]
  • Ruby 1.2: December 1998
  • Ruby 1.4: August 1999
  • Ruby 1.6: September 2000

In 1997, the first article about Ruby was published on the Web. In the same year, Matsumoto was hired by netlab.jp to work on Ruby as a full-time developer.[16]

In 1998, the Ruby Application Archive was launched by Matsumoto, along with a simple English-language homepage for Ruby.[16]

In 1999, the first English language mailing list ruby-talk began, which signaled a growing interest in the language outside of Japan.[23] In this same year, Matsumoto and Keiju Ishitsuka wrote the first book on Ruby, The Object-oriented Scripting Language Ruby (オブジェクト指向スクリプト言語 Ruby), which was published in Japan in October 1999. It would be followed in the early 2000s by around 20 books on Ruby published in Japanese.[16]

By 2000, Ruby was more popular than Python in Japan.[24] In September 2000, the first English language book Programming Ruby was printed, which was later freely released to the public, further widening the adoption of Ruby amongst English speakers. In early 2002, the English-language ruby-talk mailing list was receiving more messages than the Japanese-language ruby-list, demonstrating Ruby's increasing popularity in the English-speaking world.

Ruby 1.8

Ruby 1.8 was initially released in August 2003, was stable for a long time, and was retired June 2013.[25] Although deprecated, there is still code based on it. Ruby 1.8 is incompatible with Ruby 1.9.

Ruby 1.8 has been the subject of several industry standards. The language specifications for Ruby were developed by the Open Standards Promotion Center of the Information-Technology Promotion Agency (a

  • Official website
  • Official Ruby documentation
  • Ruby User Guide — by Yukihiro Matsumoto, the creator of Ruby
  • A community-driven Ruby coding style guide
  • Ruby From Other Languages
  • Ruby Forum — gateway to the ruby-talk mailing list
  • Try Ruby! — web-based Ruby REPL
  • Ruby Draft Specification, September 2010
  • Ruby at DMOZ

External links

  • Metz, Sandi (September 5, 2012), Practical Object-Oriented Design in Ruby (First ed.),  
  • McAnally, Jeremy; Arkin, Assaf (March 28, 2009), Ruby in Practice (First ed.),  
  • Thomas, Dave; Fowler, Chad; Hunt, Andy (April 28, 2009), Programming Ruby 1.9: The Pragmatic Programmers' Guide (Third ed.),  
  • Black, David (June 4, 2009), The Well-Grounded Rubyist (First ed.),  
  • Flanagan, David; Matsumoto, Yukihiro (January 25, 2008), The Ruby Programming Language (First ed.),  
  • Baird, Kevin (June 8, 2007), Ruby by Example: Concepts and Code (First ed.),  
  • Fitzgerald, Michael (May 14, 2007), Learning Ruby (First ed.),  
  • Cooper, Peter (March 26, 2007), Beginning Ruby: From Novice to Professional (First ed.),  
  • Fulton, Hal (November 4, 2006), The Ruby Way (Second ed.),  
  • Carlson, Lucas; Richardson, Leonard (July 19, 2006), Ruby Cookbook (First ed.),  

Further reading

  1. ^ nagachika (2014-11-13). "Ruby 2.1.5 Released". ruby-lang.org. Retrieved 13 November 2014. 
  2. ^ a b c Cooper, Peter (2009). Beginning Ruby: From Novice to Professional. Beginning from Novice to Professional (2nd ed.). Berkeley: APress. p. 101.  
  3. ^ a b c d e f Bini, Ola (2007). Practical JRuby on Rails Web 2.0 Projects: Bringing Ruby on Rails to Java. Berkeley: APress. p. 3.  
  4. ^ "Intro - D Programming Language 1.0 - Digital Mars". Digital Mars. Retrieved 2014-10-21.  
  5. ^ Bertels, Christopher (23 February 2011). "Introduction to Fancy". Rubinius blog. Retrieved 2011-07-21. 
  6. ^ Bini, Ola. "Ioke". Ioke.org. Retrieved 2011-07-21. inspired by Io, Smalltalk, Lisp and Ruby 
  7. ^ http://julia.readthedocs.org/en/latest/manual/introduction/
  8. ^ Burks, Tim. "About Nu™". Programming Nu™. Neon Design Technology, Inc. Retrieved 2011-07-21. 
  9. ^ Lattner, Chris (2014-06-03). "Chris Lattner's Homepage". Chris Lattner. Retrieved 2014-06-03. The Swift language is the product of tireless effort from a team of language experts, documentation gurus, compiler optimization ninjas, and an incredibly important internal dogfooding group who provided feedback to help refine and battle-test ideas. Of course, it also greatly benefited from the experiences hard-won by many other languages in the field, drawing ideas from Objective-C, Rust, Haskell, Ruby, Python, C#, CLU, and far too many others to list. 
  10. ^ COPYING in Ruby official source repository
  11. ^ GPL in Ruby official source repository
  12. ^ BSDL in Ruby official source repository
  13. ^ "About Ruby". Retrieved 2 March 2014. 
  14. ^ Shugo Maeda (17 December 2002). "The Ruby Language FAQ". Retrieved 2 March 2014. 
  15. ^ Yukihiro Matsumoto (13 February 2006), ruby-talk: Re: Ruby's lisp features, retrieved 2 March 2014 
  16. ^ a b c d e f http://blog.nicksieger.com/articles/2006/10/20/rubyconf-history-of-ruby History of Ruby
  17. ^ http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/88819 "[FYI: historic] The decisive moment of the language name Ruby. (Re: [ANN] ruby 1.8.1)" — E-mail from Hiroshi Sugihara to ruby-talk
  18. ^ "The Ruby Language FAQ – 1.3 Why the name 'Ruby'?". Ruby-Doc.org. Retrieved April 10, 2012. 
  19. ^ Yukihiro Matsumoto (June 11, 1999). "Re: the name of Ruby?". Ruby-Talk mailing list. http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/394. Retrieved April 10, 2012.
  20. ^ More archeolinguistics: unearthing proto-Ruby
  21. ^ "Re: history of ruby" — E-mail from Yukihiro Matsumoto to ruby-talk
  22. ^ "TUTORIAL – ruby's features" — E-mail From Yukihiro Matsumoto to ruby-list
  23. ^ http://www.linuxdevcenter.com/pub/a/linux/2001/11/29/ruby.html An Interview with the Creator of Ruby
  24. ^ Yukihiro Matsumoto (October 2000). "Programming Ruby: Forward". Retrieved 5 March 2014. 
  25. ^ a b Ruby 1.8.7 is retired
  26. ^ プログラム言語RubyのJIS規格(JIS X 3017)制定について
  27. ^ プログラム言語Ruby、国際規格として承認
  28. ^ Web Development: Ruby on Rails. Devarticles.com (2007-03-22). Retrieved on 2013-07-17.
  29. ^ "Ruby 1.9.3 p0 is released". ruby-lang.org. October 31, 2011. Retrieved February 20, 2013. 
  30. ^ "v1_9_3_0/NEWS". Ruby  
  31. ^ Ruby 1.9: What to Expect. Slideshow.rubyforge.org. Retrieved on 2013-07-17.
  32. ^ Endoh, Yusuke. (2013-02-24) Ruby 2.0.0-p0 is released. Ruby-lang.org. Retrieved on 2013-07-17.
  33. ^ Endoh, Yusuke. (2013-02-24) Ruby 2.0.0-p0 is released. Ruby-lang.org. Retrieved on 2013-07-17.
  34. ^ "Ruby 2.1.0 is released". December 25, 2013. Retrieved December 26, 2013. 
  35. ^ "Semantic Versioning starting with Ruby 2.1.0". December 21, 2013. Retrieved December 27, 2013. 
  36. ^ The Ruby Programming Language by Yukihiro Matsumoto on 2000-06-12 (informit.com)
  37. ^ Google Tech Talks – Ruby 1.9 on YouTube
  38. ^ a b c The Philosophy of Ruby, A Conversation with Yukihiro Matsumoto, Part I by Bill Venners on 2003-09-29 (Artima Developer)
  39. ^ Ruby Weekly News 23rd – 29th May 2005
  40. ^ An Interview with the Creator of Ruby
  41. ^ Dynamic Productivity with Ruby
  42. ^ martinfowler.com
  43. ^ Ruby – Add class methods at runtime
  44. ^ Blocks and Closures in Ruby
  45. ^ Unicode support in Ruby is too buggy compared to similar programming languages
  46. ^ Britt, James. "Ruby 2.0.0 Standard Library Documentation". Retrieved 2013-12-09. 
  47. ^ Green threads
  48. ^ Ruby FAQ
  49. ^ In Ruby's syntax, statement is just a special case of an expression which cannot appear as an argument (e.g. multiple assignment). http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/1120
    statement [...] can not be part of expression unless grouped within parentheses. http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/2460
  50. ^ Re: semenatics of if/unless/while statement modifiers. Blade.nagaokaut.ac.jp (2005-11-23). Retrieved on 2013-07-17.
  51. ^ Peter Cooper (2010-05-18). "The Why, What, and How of Rubinius 1.0's Release". 
  52. ^ John Lam (2008-05-25). "IronRuby / Rails Question". Retrieved 2008-05-25. 
  53. ^ John Lam (2008-05-30). "IronRuby and Rails". Retrieved 2008-06-01. 
  54. ^ Maya Stodte (February 2000). "IBM developerWorks – Ruby: a new language". Retrieved 3 March 2014. 
  55. ^ Yukihiro Matsumoto (August 2002). "lang-ruby-general: Re: question about Ruby initial development". Retrieved 3 March 2014. 
  56. ^ Yukihiro Matsumoto (5 January 1999). "ruby-talk: Re: hah, check these errors". Retrieved 3 March 2014. 
  57. ^ "Iron Ruby on Windows Phone 7". 

References

See also

Many new and existing Ruby libraries are hosted on GitHub, a service that offers version control repository hosting for Git.

RubyGems is Ruby's package manager. A Ruby package is called a "gem" and can easily be installed via the command line. There are over 70,000 Ruby gems hosted on RubyGems.org.

Repositories and libraries

Modern Ruby versions and implementations are available on many operating systems, such as Linux, BSD, Solaris, AIX, Mac OS X, Windows, Windows Phone,[57] Windows CE, Symbian OS, BeOS, and IBM i.

By 1999, Ruby was known to work across many different operating systems, including NEWS-OS, SunOS, AIX, SVR4, Solaris, NEC UP-UX, NeXTSTEP, BSD, Linux, Mac OS, DOS, Windows, and BeOS.[56]

Matsumoto originally did Ruby development on the 4.3BSD-based Sony NEWS-OS 3.x, but later migrated his work to SunOS 4.x, and finally to Linux.[54][55]

Platform support

The maturity of Ruby implementations tends to be measured by their ability to run the Ruby on Rails (Rails) framework, because it is complex to implement and uses many Ruby-specific features. The point when a particular implementation achieves this goal is called "the Rails singularity". The reference implementation (MRI), JRuby, and Rubinius[51] are all able to run Rails unmodified in a production environment. IronRuby[52][53] is starting to be able to run Rails test cases, but is still far from being production-ready.

Ruby can also run on embedded system by mruby, developing in GitHub.

Other now defunct Ruby implementations were:

Other Ruby implementations include:

  • JRuby, a Java implementation that runs on the Java virtual machine,
  • Rubinius, a C++ bytecode virtual machine that uses LLVM to compile to machine code at runtime. The bytecode compiler and most core classes are written in pure Ruby.

Ruby 1.9 has two major alternate implementations:

As of 2010, there are a number of alternative implementations of Ruby, including JRuby, Rubinius, MagLev, IronRuby, MacRuby (and its iOS counterpart, RubyMotion), mruby, HotRuby, Topaz and Opal. Each takes a different approach, with IronRuby, JRuby, MacRuby and Rubinius providing just-in-time compilation and MacRuby and mruby also providing ahead-of-time compilation.

Alternate implementations

Starting with Ruby 1.9, and continuing with Ruby 2.0 and 2.1, the official Ruby interpreter has been YARV ("Yet Another Ruby VM"), and this implementation has superseded the slower virtual machine used in previous releases of MRI.

The standardized and retired Ruby 1.8 implementation was written in C, as a single-pass interpreted language.[25]

The official Ruby interpreter often referred to as the Matz's Ruby Interpreter or MRI. This implementation is written in C and uses its own Ruby-specific virtual machine.

Matz's Ruby Interpreter

Implementations

More sample Ruby code is available as algorithms in the following articles:

More examples

  • intercepting and modifying method calls
  • implementing new inheritance models
  • dynamically generating classes from parameters
  • automatic object serialization
  • interactive help and debugging

Some other possible uses for Ruby metaprogramming include:

To implement the equivalent in many other languages, the programmer would have to write each method (in_black, in_red, in_green, etc.) separately.

"Hello, World!".in_blue
 => "Hello, World!"

The generated methods could then be used like this:

COLORS = { black:   "000",
           red:     "f00",
           green:   "0f0",
           yellow:  "ff0",
           blue:    "00f",
           magenta: "f0f",
           cyan:    "0ff",
           white:   "fff" }

class String
  COLORS.each do |color,code|
    define_method "in_#{color}" do
      "#{self}"
    end
  end
end

For example, the following Ruby code generates new methods for the built-in String class, based on a list of colors. The methods wrap the contents of the string with an HTML tag styled with the respective color.

Ruby code can programmatically modify, at runtime, aspects of its own structure that would be fixed in more rigid languages, such as class and method definitions. This sort of metaprogramming can be used to write more concise code and effectively extend the language.

Metaprogramming

begin
  # do something
rescue RuntimeError, Timeout::Error => e
  # handling, possibly involving e
end

Several exceptions can also be caught:

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

begin
  # do something
rescue RuntimeError => e
  # handling, possibly involving e, such as "puts e.to_s"
end

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

begin
  # do something
rescue RuntimeError
  # handle only RuntimeError and its subclasses
end

Or catch particular exceptions:

begin
  # do something
rescue Exception
  # Exception handling code here.
  # Don't write only "rescue"; that only catches StandardError, a subclass of Exception.
end

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
  # handle exception
else
  # do this if no exception was raised
ensure
  # do this whether or not an exception was raised
end

Exceptions are handled by the rescue clause. Such a clause can catch exceptions which inherit from StandardError. Other flow control keywords that can be used when handling exceptions are else and ensure:

class ParseError < Exception
  def initialize input, line, pos
    super "Could not parse '#{input}' at line #{line}, position #{pos}"
  end
end

raise ParseError.new("Foo", 3, 9)

This last construct is useful when a custom exception class featuring a constructor which takes more than one argument needs to be raised:

raise ArgumentError.new("Illegal arguments!")

Alternatively, an exception instance can be passed to the raise method:

raise ArgumentError, "Illegal arguments!"

Exceptions can also be specified by the programmer:

raise "This is a message"

An optional message can be added to the exception:

raise

An exception is raised with a raise call:

Exceptions

Adding methods to previously defined classes is often called monkey-patching. However, if performed recklessly, this practice can lead to collisions of behavior and subsequent unexpected results, and problems with code scalability.

# re-open Ruby's Time class
class Time
  def yesterday
    self - 86400
  end
end

today = Time.now               # => 2013-09-03 16:09:37 +0300
yesterday = today.yesterday    # => 2013-09-02 16:09:37 +0300

In Ruby, classes are never closed: methods can always be added to an existing class. This applies to all classes, including the standard, built-in classes. All that is needed to do is open up a class definition for an existing class, and the new contents specified will be added to the existing contents. A simple example of adding a new method to the standard library's Time class:

Open classes

Person is a constant and is a reference to a Class object.

Bob (33)
Ash (23)
Chris (16)

The preceding code prints three names in reverse age order:

class Person
  attr_reader :name, :age
  def initialize(name, age)
    @name, @age = name, age
  end
  def <=>(person) # the comparison operator for sorting
    age <=> person.age
  end
  def to_s
    "#{name} (#{age})"
  end
end

group = [
  Person.new("Bob", 33),
  Person.new("Chris", 16),
  Person.new("Ash", 23)
]

puts group.sort.reverse

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, but attr_reader only getter methods. The last evaluated statement in a method is its return value, allowing the omission of an explicit return statement.

Classes

(1..5).map(&:to_f)  # => [1.0, 2.0, 3.0, 4.0, 5.0]

Or invoke a method on each item (map is a synonym for collect):

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

Using an enumeration and a block to square the numbers 1 to 10 (using a range):

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, which then becomes sum on the next pass. It is added to 3 to get 14, which is then added to 5 on the third pass, to finally return 19.

[1,3,5].inject(10) {|sum, element| sum + element}   # => 19

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

a = [1, 'hi', 3.14, 1, 2, [4, 5]]

a[2]             # => 3.14
a.[](2)          # => 3.14
a.reverse        # => " }
# prints:
# 0: 1
# 1: 'hi'
# 2: 3.14

# The following uses a Range
(3..6).each {|num| puts num }
# prints:
# 3
# 4
# 5
# 6

Constructing and using an array:

Collections

a = 'This is a single-quoted string'
a = %q{This is a single-quoted string}

The following assignments are equivalent and produce raw strings:

var = 3.14159
"pi is #{var}"
=> "pi is 3.14159"

Strings support variable interpolation:

a = "\nThis is a double-quoted string\n"
a = %Q{\nThis is a double-quoted string\n}
a = %{\nThis is a double-quoted string\n}
a = %/\nThis is a double-quoted string\n/
a = <<-BLOCK

This is a double-quoted string
BLOCK

The following assignments are equivalent:

There are a variety of ways to define strings in Ruby.

Strings

puts "Give me a number"
number = gets.chomp
puts number.to_i
output_number = number.to_i + 1
puts output_number.to_s + ' is a bigger number.'

Conversions:

# Everything, including a literal, is an object, so this works:
-199.abs                                                 # => 199
"ice is nice".length                                     # => 11
"ruby is cool.".index("u")                               # => 1
"Nice Day Isn't It?".downcase.split("").uniq.sort.join   # => " '?acdeinsty"

Some basic Ruby code:

puts "Hello World!"

Classic Hello world example:

The following examples can be run in a Ruby shell such as Interactive Ruby Shell, or saved in a file and run from the command line by typing ruby .

Examples

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

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:

Interaction

A list of so-called gotchas may be found in Hal Fulton's book The Ruby Way, 2nd ed (ISBN 0-672-32884-4), Section 1.5. A similar list in the 1st edition pertained to an older version of Ruby (version 1.6), some problems of which have been fixed in the meantime. For example, retry now works with while, until, and for, as well as with iterators.

  • The usual operators for conditional expressions, "and" and "or", do not follow the normal rules of precedence: and does not bind tighter than or. Ruby also has expression operators || and && that work as expected.

Some features which differ notably from other languages:

  • Versions prior to 1.9 use plain integers to represent single characters, much like C. This may cause surprises when slicing strings: "abc"[0] yields 97 (the ASCII code of the first character in the string); to obtain "a" use "abc"[0,1] (a substring of length 1) or "abc"[0].chr.
  • The notation statement until expression does not run the statement if the expression is already true. (The behavior is like Perl, but unlike other languages' equivalent statements, e.g. do { statement } while (!(expression)); in C/C++/...). This is because statement until expression is actually syntactic sugar over until expression; statement; end, the equivalent of which in C/C++ is while (!(expression)) { statement; }, just as statement if expression is equivalent to if (expression) { statement; }. However, the notation begin statement end until expression in Ruby will in fact run the statement once even if the expression is already true, acting similar to the do-while of other languages. (Matsumoto has expressed a desire to remove the special behavior of begin statement end until expression,[50] but it still exists as of Ruby 2.0.)
  • Because constants are references to objects, changing what a constant refers to generates a warning, but modifying the object itself does not. For example, Greeting << " world!" if Greeting == "Hello" does not generate an error or warning. This is similar to final variables in Java or a const pointer to a non-const object in C++, but Ruby provides the functionality to "freeze" an object, unlike Java.
A consequence of 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.
  • Boolean non-boolean datatypes are permitted in boolean contexts (unlike in e.g. Smalltalk and Java), but their mapping to boolean values differs markedly from some other languages: 0 and "empty" (e.g. empty list, string or associative array) all evaluate to true, thus changing the meaning of some common idioms in related or similar languages such as Lisp, Perl and Python.
(In Ruby, integer literals are objects that can have methods apply to them, so requiring a digit after a decimal point helps to clarify whether 1.e5 should be parsed analogously to 1.to_f or as the exponential-format floating literal 1.0e5. The reason for requiring a digit before the decimal point is less clear; it might relate either to method invocation again, or perhaps to the .. and ... operators, for example in the fragment 0.1...3.)
  • The language syntax is sensitive to the capitalization of identifiers, in all cases treating capitalized variables as constants. Class and module names are constants and refer to objects derived from Class and Module.
  • The sigils $ and @ do not indicate variable data type as in Perl, but rather function as scope resolution operators.
  • Floating point literals must have digits on both sides of the decimal point: neither .5 nor 2. are valid floating point literals, but 0.5 and 2.0 are.

Some features which differ notably from languages such as C or Perl:

Differences from other languages

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

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’s design forces 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.

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 created with a single line of code via metaprogramming; however, accessor methods can also be created in the traditional fashion of C++ and Java. 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.

The syntax of Ruby is broadly similar to that of Perl and Python. Class and method definitions are signaled by keywords. In contrast to Perl, variables are not obligatorily prefixed with a sigil. When used, the sigil changes the semantics of scope of the variable. One difference from C and Perl is that keywords are typically used to define logical code blocks, without braces (i.e., pair of { and }). For practical purposes there is no distinction between expressions and statements.[49] Line breaks are significant and taken as the end of a statement; a semicolon may be equivalently used. Unlike Python, indentation is not significant.

Syntax

According to the Ruby FAQ,[48] "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, you may or may not be put off by the huge difference in design philosophy between Python and Ruby/Perl."

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, closures, and continuations; statements all have values, and functions return the last evaluation). It has support for introspection, reflection and metaprogramming, as well as support for interpreter-based[47] threads. Ruby features dynamic typing, and supports parametric polymorphism.

Ruby is object-oriented: every value is an object, including classes and instances of types that many other languages designate as primitives (such as integers, booleans, and "null"). Variables always hold references to objects. Every function is a method and methods are always called on an object. Methods defined at the top level scope become members of the Object class. Since this class is an ancestor of every other class, such methods can be called on any object. They are also visible in all scopes, effectively serving as "global" procedures. Ruby supports inheritance with dynamic dispatch, mixins and singleton methods (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 modules as mixins.

Semantics

Features

Everyone has an individual background. Someone may come from Python, someone else may come from Perl, and they may be surprised by different aspects of the language. Then they come up to me and say, 'I was surprised by this feature of the language, so Ruby violates the principle of least surprise.' Wait. Wait. The principle of least surprise is not for you only. The principle of least surprise means principle of least my surprise. And it means the principle of least surprise after you learn Ruby very well. For example, I was a C++ programmer before I started designing Ruby. I programmed in C++ exclusively for two or three years. And after two years of C++ programming, it still surprises me.

Matsumoto defined it this way in an interview:[38]

Ruby is said to follow the principle of least astonishment (POLA), meaning that the language should behave in such a way as to minimize confusion for experienced users. Matsumoto has said his primary design goal was to make a language which he himself enjoyed using, by minimizing programmer work and possible confusion. He has said that he had not applied the principle of least astonishment to the design of Ruby,[38] 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 newsgroup comp.lang.ruby, Matsumoto attempted to distance Ruby from POLA, explaining that because any design choice will be surprising to someone, he uses a personal standard in evaluating surprise. If that personal standard remains consistent, there would be few surprises for those familiar with the standard.[39]

Often people, especially computer engineers, focus on the machines. They think, "By doing this, the machine will run fast. By doing this, the machine will run more effectively. By doing this, the machine will something something something." They are focusing on machines. But in fact we need to focus on humans, on how humans care about doing programming or operating the application of the machines. We are the masters. They are the slaves.

Matsumoto has said that Ruby is designed for programmer productivity and fun, following the principles of good user interface design.[36] At a Google Tech Talk in 2008 Matsumoto further stated, "I hope to see Ruby help every programmer in the world to be productive, and to enjoy programming, and to be happy. That is the primary purpose of Ruby language."[37] He stresses that systems design needs to emphasize human, rather than computer, needs:[38]

Yukihiro Matsumoto, the creator of Ruby

Philosophy

Ruby 2.1.0 was released on Christmas Day in 2013.[34] The release includes speed-ups, bugfixes, and library updates. Starting with 2.1.0, Ruby is using semantic versioning.[35]

Ruby 2.1

Ruby 2.0 is intended to be fully backward compatible with Ruby 1.9.3. As of the official 2.0.0 release on February 24, 2013, there were only five known (minor) incompatibilities.[33]

  • method keyword arguments,
  • a new method, Module#prepend, for extending a class,
  • a new literal for creating an array of symbols,
  • new API for the lazy evaluation of Enumerables, and
  • a new convention of using #to_h to convert objects to Hashes.[32]

Ruby 2.0 added several new features, including:

Ruby 2.0

  • block local variables (variables that are local to the block in which they are declared)
  • an additional lambda syntax: f = ->(a,b) { puts a + b }
  • per-string character encodings are supported
  • new socket API (IPv6 support)
  • require_relative import security

Ruby 1.9 introduces many significant changes over the 1.8 series.[31] Examples:

Ruby 1.9 was released in December 2007. Effective with Ruby 1.9.3, released October 31, 2011,[29] Ruby switched from being dual-licensed under the Ruby License and the GPL to being dual-licensed under the Ruby License and the two-clause BSD license.[30] Adoption of 1.9 was slowed by changes from 1.8 which required many popular third party gems to be rewritten.

Ruby 1.9

Around 2005, interest in the Ruby language surged in tandem with Ruby on Rails, a web application framework written in Ruby. Rails is frequently credited with increasing awareness of Ruby.[28]

[27]) in 2012.ISO/IEC 30170 and an international standard ([26]

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