OOP and Ruby
Guillaume FAURE-DUMONT
@guillaume_fd
What is POO ?
Business coding !
-
Encapsulation
-
Inheritance
-
Polymorphism
POO principles
Encapsulation (1/6)
Define a concept: CLASS
It's a whole that holds itself together with Properties:
- Variables (data)
- Methods (mechanism)
We can create instances of this concept: Objects
new_instance = Myclass.new
Constructor method: initialize
Encapsulation (2/7)
class vehicle
def initialize(wheels_number, speed)
@wheels_number = wheels_number
@speed = speed
@position = 0
@direction = 1
end
def describe
puts "This vehicle has #{@wheels_number} wheels"
puts "Position: #{@position} from origin"
end
def move_forward
@position = @position + @speed * @direction
puts "Position: #{@position} from origin"
end
end
$ my_car = Vehicle.new(4, 150)
$ my_car.describe
This vehicle has 4 wheels
Position: 0 from origin
$ my_car.move_forward
Position: 100 from origin
Internal mechanism have to be ...internal !
"I don't care how you do it, just gimme the result"
Don't speak to strangers (law of Demeter)
Hide your mechanism with private & protected methods
Encapsulation (3/7)
Encapsulation (4/7)
class vehicle
def describe
puts "This vehicle has #{@wheels_number} wheels"
write_position
end
def move_forward
@position = @position + @speed * @direction
write_position
end
private
def write_position
puts "Position: #{@position} from origin"
end
end
$ my_car = Vehicle.new(4, 150)
$ my_car.write_position
NoMethodError: private method `write_position' called for #<Car:0x00000002d211b0>
$ my_car.describe
This vehicle has 4 wheels
Position: 0 from origin
Encapsulation (5/7)
Some code is only about the class and not it's instances
Math::PI
Math::E
WARNING:
class methods cannot access instance attributes !
Encapsulation (6/7)
class Vehicle
VERSION = 42.0
@@vehicle_number = 0
def initialize(wheels_number, speed)
...
@@vehicle_number += 1
end
def describe
...
self.class.display_vehicle_count
end
def self.display_vehicle_count
puts "There are now #{@@vehicle_number} vehicle(s) in memory"
end
end
$ Vehicle::VERSION
42.0
$ Vehicle::display_vehicle_count
There are now 0 vehicle(s) in memory
Encapsulation (7/7)
module Thp
class Vehicle
VERSION = 42.0
...
end
end
Modules allow to gather Classes in bigger sets
Inheritance (1/2)
Think in Funnels
Start big, go into details with the flow
Create global concepts first
Car < Vehicle
and reuse ancestor's properties
(Don't Repeat Yourself)
Inheritance (2/2)
class Vehicle
def initialize(wheels_number, speed)
@wheels_number = wheels_number
@speed = speed
end
...
end
class Car < Vehicle
def initialize(speed)
@wheels_number = 4
@speed = speed
end
end
class Motocycle < Vehicle
def initialize(speed)
super 2, speed
end
end
Polymorphism (1/2)
Having different reactions based on given parameters
and ... Overriding ;)
Polymorphism (2/2)
Having different reactions based on given parameters
class Train < Vehicle
def initialize
super 16, 2000
@direction = 1
end
def set_direction(new_direction)
puts 'This vehicle cannot change direction'
end
def move_forward
@position = @position + @speed
write_position
end
end
Some Ruby Specifics
Having different reactions based on given parameters
# supervehicle.rb
class Vehicle
def describe
puts "\nThis vehicle is a #{self.class}"
puts "Its superclass is #{self.class.superclass}"
puts "It has #{@wheels_number} wheels"
write_position
self.class.display_vehicle_count
end
end
OOP and Ruby
By Guillaume Faure-Dumont
