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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.
History 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 October 2006, the latest stable version is 1.8.5. Ruby 1.9 (with some major changes) is also in development. Philosophy Matz's primary design consideration is to make programmers happy by reducing the menial work they must do, following the principles of good user interface design. He stresses that systems design needs to emphasize human, rather than computer, needs Ruby is said to follow the principle of least surprise (POLS), meaning that the language typically behaves intuitively or as the programmer assumes it should. The phrase did not originate with Matz and, generally speaking, Ruby may more closely follow a paradigm best termed as "Matz's Least Surprise", though many programmers have found it to be close to their own mental model as well. Matz defined it this way in an interview: Semantics Ruby is object-oriented: every bit of data is an object, even classes and types that many other languages designate as primitives (such as integers, booleans, and "nil"). Every function is a method. Named values (variables) always designate references to objects, not the objects themselves. 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. Procedural syntax is supported, but everything done in Ruby procedurally (that is, outside of the scope of a particular object) is actually done to an Object instance named 'main'. 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 you to program procedurally (defining functions/variables outside classes makes them part of the root, 'self' Object), with object orientation (everything is an object) or functionally (it has anonymous functions, closures, and continuations; statements all have values, and functions return the last evaluation). It has support for introspection, reflection and meta-programming, as well as support for threads. Ruby features dynamic typing, and supports parametric polymorphism. According to the 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, you may or may not be put off by the huge difference in design philosophy between Python and Ruby/Perl." Features 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. A session with this interactive program might be: $ irb irb(main):001:0> puts "Hello, World" Hello, World => nil irb(main):002:0> 1+2 => 3 There also exist readline bindings (module Readline), easily allowing the user for custom shells with history support. Readline.readline(, true) 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. (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 brackets. Line breaks are significant and taken as the end of a statement; a semicolon may be equivalently used. Indentation is not significant (unlike Python). See the Examples section for samples of code demonstrating Ruby syntax. Gotchas and possible surprises Although Ruby's design is guided by the principle of least surprise, naturally, some features differ from languages such as C or Perl: 99.0) or an explicit conversion (99.to_f). It is insufficient to append a dot (99.) because numbers are susceptible to method syntax."" and 0 ? 1 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 however only the special objects true and false can be used in a boolean expression.
char for characters). This may cause surprises when slicing strings: "abc"0 yields 97 (an integer, representing 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.In addition, some issues with the language itself are commonly raised: A good list of "gotchas" may be found in Hal Fulton's book The Ruby Way, pages 48-64 (ISBN 0672328844). However, since the list in the book pertains to an older version of Ruby (version 1.6), some items have been fixed since the book's publication. For example, retry now works with while, until and for, as well as iterators.Examples Some basic Ruby code: Collections Constructing and using an array: a = a2 Constructing and using a hash: hash = hash.each_pair do |key, value| hash.delete_if water => 'wet Blocks and iterators The two syntaxes for creating a code block: do puts "Hello, World!" end Parameter-passing a block to be a closure: @block = b end Returning closures from a method: def foo(initial_value=0) var = initial_value return Proc.new , Proc.new end setter, getter = foo setter.call(21) getter.call Yielding the flow of program control to a block which was provided at calling time: def a( &block ) yield block( "hello") end u.edge_iterator do |v| if not v.marked? yield v q.push v end end end end bfs(e) Iterating over enumerations and arrays using blocks: a = 1, 'hi', 3.14 a.each Blocks work with many built-in methods: File.open('file.txt', 'w+b') do |file| file.puts 'Wrote some text.' end Or: File.readlines('file.txt').each do |line| Using an enumeration and a block to square the numbers 1 to 10: (1..10).collect => 1, 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 can sort by age) and the other to override the to_s method (so Kernel can format its output). Here, "attr_reader" is an example of meta-programming in Ruby: "attr" 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 Person def initialize(name, age) @name, @age = name, age end def <=>(person) @age <=> person.age end def to_s " attr_reader name,age end group = puts group.sort.reverse The above prints three names in reverse age order: Markus (63) John (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 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 Or particular exceptions: begin Finally, it is possible to specify that the exception object be made available to the handler clause: begin Alternatively, the most recent exception is stored in the magic global $!.More examples More sample Ruby code is available as algorithms in the following articles: Implementations Ruby has two main implementations: the official Ruby interpreter, which is the most widely used, and JRuby, a Java-based implementation. Operating systems Ruby is available for the following operating systems: Other ports may also exist. Licensing terms The Ruby interpreter and libraries are distributed disjointedly (dual licensed) under the free and open source licenses GPL and Ruby License . 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 community, there is 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. Sample scripts For sample ruby scripts, use the Google Code Search: Start here: and if you need so, add additional parameters to the address. For example to find scripts which use Win32API use: The Google Code Search will let you locate and preview ruby code which is stored on the Internet, including code stored in ZIP files. See also Notes | |||||||||||||||||||||||||||||||||||||
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