Ruby :: Training 1

TRAINING 1
RUBY
Pavel Tsiukhtsiayeu
github.com/paveltyk

Ruby :: introduction
• Ruby is a object oriented language
• Truly OBJECT ORIENTED language !!!
• Designed and developed by Yukihiro “Matz” Matsumoto

• 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

• 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

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

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”

Ruby :: truly object oriented
• Everything is an object. Everything!
• 1.class => Fixnum
• “hello”.class => String
• [1, „hello‟, nil].class => Array
• nil.class => NilClass
• true.class => TrueClass
• false.class => FalseClass
• (1..10).class => Range
• /hello/.class => Regexp
• Fixnum.class => Class
• Class.class => Class %)) WHAT!!

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

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”)

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

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]

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.

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

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

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

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

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‟]

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 …

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”

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

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

Ruby :: Blocks
• Blocks are heavily used in Ruby
• Callbacks
• after_create lambda { |u| u.send_message }
• before_validate lambda { |u| u.clear_name }
• Template functions
• [1,2,3].map { |a| a * 2 } #=> [2,4,6]
• [1,2,3].all? { |a| a > 2 } #=> false
• Wrapping logic
• File.open(„hello.txt‟, „w‟) { |f| f.puts „Hello‟ }
• Lazy evaluation
• Rails.cache.fetch(:jobs) { heavy_task }

Ruby :: alternative syntax
• Array
• [„cat‟, „dog‟]
• %w(cat dog) - parentheses may vary: %w{..} %w[..] %w!..!
• %W(cat #{var} dog)
• Regexp
• /^cat/
• %r(^cat) - parentheses may vary
• String
• „Hello, World‟ and “Hello, Word!”
• %q(Hello, World!) - single quoted string
• %Q(Hello, World!) - double quoted string (interpolation occurs)
• %(Hello, World!)
• <<HERE_DOC
• Hello, World!
• HERE_DOC

Ruby :: what do I do next?
• http://tryruby.org
• http://koans.heroku.com

Ruby :: Training 1

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