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Ruby programming language

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Ruby is a reflective, object-oriented programming language. It combines syntax inspired by Ada and 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.

Contents

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 June 2006, the latest stable version is 1.8.4. 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. [link] He stresses that systems design needs to emphasize human, rather than computer, needs [link]:

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." [link]

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

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 obligatorially 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:

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. 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:

# Everything, including literals, is an object, so this works:
-199.abs                                       # 199
"ruby is cool".length                          # 12
"Rick".index("c")                              # 2
"Nice Day Isn't It?".split(//).uniq.sort.join  # " '?DINaceinsty"

Collections

Constructing and using an array: 

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


a[2]                      # 3.14
a.reverse                 # [[4, 5], 2, 1, 3.14, 'hi', 1]
a.flatten.uniq            # [1, 'hi', 3.14, 2, 4, 5]
Constructing and using a hash: 
hash = 
puts hash[:fire]       # Prints:  hot


hash.each_pair do |key, value|
puts "# is #"
end


# Prints:             water is wet
#                     fire is hot


hash.delete_if    # Deletes :water => 'wet'

Blocks and iterators

The two syntaxes for creating a code block: 



do puts "Hello, World!" end
Passing a block as a parameter (to be a closure): 
def remember(&p)
@block = p
end
# Invoke the method, giving it a block that takes a name.
remember !"}


# When the time is right -- call the closure!
@block.call("John")
# Prints "Hello, John!"
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 # => 21
Yielding program flow to a block provided at the location of the call: 
def bfs(e)
q = []
e.mark
yield e
q.push e
while not q.empty?
u = q.shift
u.edge_iterator do |v|
if not v.marked?
v.mark
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           # Prints each element
(3..6).each        # Prints the numbers 3 through 6
[1,3,5].inject(0)  # 9, (you can pass both a parameter and a block)
Blocks work with many built-in methods: 
File.open('file.txt', 'w+b') do |file|
file.puts 'Wrote some text.'
end                             # File automatically closed here
Or: 
File.readlines('file.txt').each do |line|
# Process each line, here.
end
Using an enumeration and a block to square 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#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 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
"# (#)"
end


attr_reader :name, :age
end


group = [ Person.new("John", 20),
Person.new("Markus", 63),
Person.new("Ash", 16)
]


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
# 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
# Handle exception
end
Or particular exceptions: 
begin
# ...
rescue RuntimeError
# handling
end
Finally, it is possible to specify that the exception object be made available to the handler clause: 
begin
# ...
rescue RuntimeError => e
# handling, possibly involving e
end
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. The Ruby interpreter has been ported to many platforms, including Unix, Microsoft Windows, DOS, Mac OS X, OS/2, Amiga and many more.

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 under the free and open source licenses GPL and Ruby License [link].

Applications

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.

See also

  1. redirect[[Template:Portal]]

Notes

External links

  1. redirect [[Template:Wikibooks]]

 

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.

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