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Ruby is an 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 and CLU. It was originally designed as an interpreted language, though in its JRuby implementation it may be compiled.
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. He chose the name to reflect the language's Perl heritage. According to the author, he designed Ruby to follow the principle of least surprise, meaning that the language should be free from the traps and inconsistencies that plague other languages. As of December 2004, the latest stable version is 1.8.2.
Philosophy
Ruby is object-oriented: every bit of data is an object, including types other languages designate primitive such as integers. Every function is a method. Named values (variables) designate references to objects, not the objects themselves. Ruby supports inheritance with dynamic dispatch, mixins and singleton methods (belonging to a class rather than an instance). Though Ruby does not support multiple inheritance, classes can import modules as mixins. Procedural syntax is included, but everything done in Ruby procedurally (i.e., outside of the scope of a particular object) is actually done to the Object class. Since this class is parent to every other class, the changes become visible to all classes and objects.
Ruby has also 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 rich support for introspection, reflection and meta-programming.
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."
Implementations
Ruby has two main implementations: the official Ruby interpreter, which is the most widely used, and JRuby, a Java-based implementation. The former has been ported to many platforms, including Unix, Microsoft Windows, DOS, Mac OS X, OS/2, Amiga and many more. The Ruby distribution also includes "IRB", an interactive command-line interpreter which can be used to test code quickly.
Licensing terms
Ruby is distributed disjointly under the free and open source licenses GPL and Ruby License [1] (http://www.ruby-lang.org/en/LICENSE.txt).
Features
Ruby currently lacks support for Unicode, though it has partial support for UTF-8.
Possible surprises
Although Ruby's design has been guided by the principle of least surprise, naturally there are features differing from languages such as C or Perl:
- Local variable names may not begin with a capital letter, otherwise they are treated as constants.
- 0, "" and [] are true: In C, the expression 0 ? 1 : 0 is evaluated as 0. In Ruby, however, it yields 1. Reasoning: In Ruby, many expressions (e.g., regular expression tests) return either a numeric value, string or array, or "nil". When such a return value is evaluated in a boolean context, only "nil" is evaluated as "false": every numeric (string or array) value, including zero (0, empty string, "", or array, []) is considered "true". Coincidently, as in Java, C- and Perl-style automatic conversion from numerics, strings and arrays to boolean "false" does not work.
- To indicate floating point numbers, it is insufficient to append a dot (99.). Because numbers are susceptible to method syntax, one must follow with a zero digit (99.0) or an explicit conversion (99.to_f).
- There is no character (char) data type. This may cause surprises when slicing strings: "abc"[0] yields 97 (an integer, representing the ASCII code of the first character in the string); use "abc"[0,1] to obtain "a" (a substring of length 1).
Maybe the best "Gotcha list" is to be found in Hal Fulton's "Ruby Way" book, pages 48-64. There's a fair number of things to get used to if one is used to Perl, Python, Java, or Smalltalk. However, the list in the book pertains to Ruby 1.6, and some items have changed in Ruby 1.8 and later. For example, "retry" now works with "while", until", "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 = {'water' => 'wet', 'fire' => 'hot'}
puts hash['fire']
hash.each_pair 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
Two ways to make blocks:
{puts "Hello, World!"}
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 {|name| puts "Hello, " + name + "!"}
# When the time is right -- call the closure!
@block.call("Johnny")
# Prints "Hello, Johnny!"
Iterating over enumerations and arrays using blocks:
a =[1, 'hi', 3.14]
a.each {|item| puts item} # Prints each element
(3..6).each {|num| puts num} # Prints the numbers 3 through 6
Blocks work with many built-in methods:
IO.readlines('file.txt') do |line|
# Process each line, here.
end
Using an enumeration and a block to square 1 to 10:
(1..10).collect {|x| x*x} => [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.
class Person
def initialize(name, age)
@name, @age = name, age
end
def <=>(person)
@age <=> person.age
end
def to_s
"#{@name} (#{@age})"
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)
More sample Ruby code is available as algorithms in the following articles:
Hello World
puts "Hello World!"
External links
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