2. Ruby :: introduction
• Ruby is a object oriented language
• Truly OBJECT ORIENTED language !!!
• Designed and developed by Yukihiro “Matz” Matsumoto
3. Ruby :: introduction
• Yukihiro “Matz” Matsumoto
• まつもとゆきひろ 松本行弘
• Born 14 Apr 1965
• As of 2012, Matsumoto is the
Chief Architect of Ruby at Heroku
• https://github.com/matz
• https://twitter.com/yukihiro_matz
4. Ruby :: introduction
• Ruby is a object oriented language
• Truly OBJECT ORIENTED language !!!
• Designed and developed by Yukihiro “Matz” Matsumoto
• Ruby written for humans, not machines
• Often … computer engineers … focus on the machines. But in fact
we need to focus on humans… We are the masters. They are the
slaves.
• Rich yet Flexible Syntax
• 3.downto(0) { |i| puts "Countdown: #{i}..."}
• user = User.find_by_name(„Matz‟) and user.say_hi
• Ruby makes developers HAPPY
5. Ruby :: variables and constants
• Sigils denote scopes
• Sigil - symbol attached to variable name
• $ - global ($global_variable)
• @ - instance variable (@instance_variable)
• @@ - class variable (@@class_variable)
• [A-Z] - constants
• CONSTANT - all upper case
• MyClass - titleized
• [_a-z] - local variables (local_variable)
• You never see variable declarations
• But you always know what you are dealing with
• Clean and Readable code
6. Ruby :: methods, naming convention
• object.find_by_name - preferable snake case
• object.dangerous! - Bang!!! method
• object.boolean_predicate? - returns true or false
def Name # do not do this
“I‟m a method”
end
Name = “I‟m a constant”
Name
#=> “I‟m a constant”
Name()
#=> “I‟m a method”
8. Ruby :: nil is an object
• nil.to_s => “”
• nil.to_i => 0
• nil.nil? => true
• nil.blank? => true (Rails extension)
• In statements (if, case, etc.) only nil and false evaluated
as FALSE
9. Ruby :: syntax
• Almost everything can be written in different ways
• Easy things stay clean and easy
• Difficult things maintain readability
• Parentheses are optional
• find_by_name 'Matz'
• find_by_name('Matz')
• Blocks
• { |a| #do something with a }
• do |a|
• #do something with a
• end
• 1..5 eq Range.new(1,5) and /^Hi/ eq Regexp.new(“^Hi”)
10. Ruby :: syntax sugar
• Did you ever do?
• puts “Hello, World!”
• puts - is it a language construct?
• It‟s a method defined in Kernel :)
• public, private, protected - language constructs?
• No! They are class methods!
• +, -, *, ==, etc. are methods too :)
• 1 + 2 equivalent to 1.+(2) equivalent to 1.send :+, 2
• =, .., ..., !, not, &&, and, ||, or, !=, !~ What about these?
• These are REAL operators
11. Ruby :: classes
• Ready to know the truth?
class MyClass MyClass = Class.new do
def name def name
“MyClass” “MyClass”
end end
end end
• Classes are instances of a class Class
• Class.ancestors =>
• [Class, Module, Object, Kernel, BasicObject]
12. Ruby :: open classes
• Classes in Ruby are always open
• Change them any time (avoid monkey patching core
classes)
nil.dance #=> NoMethodError
class NilClass
def dance
“Spin”
end
end
nil.dance #=> “Spin”
• Rails adds many handy methods to core Ruby classes:
• blank?, present?, presence, etc.
13. Ruby :: inheritance
• Ruby has NO multiple inheritance
• Ruby has single inheritance + MIXINS
• By default all classes inherit from Object
• Object inherit from BasicObject (ruby 1.9)
• Object.instance_methods.size => 112
• BasicObject.instance_methods.size => 7
14. Ruby :: inheritance, message dispatching
• kate.dance
BasicObject
• kate.send :dance
Object
my_object.method_missing
my_object.send :dance MyClass
• What happens if method not found?
• Exception raised: NoMethodError
15. Ruby :: self & method missing
• self = current object
• Every method has 3 parts: object.do_the_thing(10)
• object - receiver
• do_the_thing - message
• 10 - arguments
• receiver is self, if not explicit receiver given
• What method_missing can be useful for
• Person.find_by_name(„Matz‟)
• Write DSL (XML generators)
• Proxy pattern
• Method delgation
16. Ruby :: modules
• A namespace for constants (such as classes)
• A place to define methods (can be later used by a class or
an object)
• Unlike a class, can‟t have instances & instance variables
• Class (as a class name) inherit from class Module
• Class (as a class name) has more functionality (#new for example)
• A key element of MIXIN
module Dance Dance = Module.new do
def do_the_trick def do_the_trick
“Back flip” “Back flip”
end end
end end
17. Ruby :: MIXINS
• Mixins are used widely in Ruby
• Please behave like Enumerable: include Enumerable
class Band find | detect
include Enumerable find_all | select
map | collect
attr_accessor :members inject, reject
all? any? one? none?
def each(&block) min max
members.each{ |member| block.call(member) }
end AND MORE
end
metallica = Band.new
metallica.members = [„James‟, „Lars‟, „Kirk‟, „Robert‟]
metallica.find_all { |m| m.size > 4 }
#=> [„James‟, „Robert‟]
18. Ruby :: MIXINS
• What happens when you include a module?
• class Band;end
• Band.ancestors => [Band, Object, Kernel, BasicObject]
• class Band
• include Enumerable
• end
• Band.ancestors =>
• [Band, Enumerable, Object, Kernel, BasicObject]
• Ruby creates an anonymous proxy class (“include” class)
containing the module‟s methods: Enumerable
• Ruby inserts this proxy class in the inheritance chain right
above current class: Band < Enumerable < Object …
19. Ruby :: MIXIN
• Try to solve this
module A Object
def name; “I‟m A”; end
end
module B Object
A
def name; “I‟m B”; end
end
class MyClass
Object
B
A
include A
Include B
end
MyClass
MyClass.new.name => “I‟m B”
20. Ruby :: MIXINS & eigenclasses
• You can extend individual object with module‟s methods
module Dancer
def dance
“Swing”
end
end
class Cat
end
jane = Cat.new
jane.extend(Dancer)
jane.dance #=> “Swing”
bob = Cat.new
bob.dance #=> ???
NoMethodError
• Ruby created eigenclass, and added proxy class
• (jane eigenclass) < (Dancer) < Cat
21. Ruby :: MIXINS & eigenclasses
• You can define methods on individual objects
class Cat
end
jane = Cat.new
def jane.dance
“Crawl”
end
jane.dance #=> “Crawl”
bob = Cat.new
bob.dance #=> NoMethodError
• jane‟s eigenclass now has #dance method
