Ruby on Rails 網站程式設計基礎班

LESSON 4

Quiz 1

Class Methods

# class 可以想像成是物件的模板/藍圖，但是他本身也可以被定義一些 method

class Person
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  # 定義 class 自己的 method
  def self.hello
    puts "hello, i am Person Class"
  end
end

# 呼叫方式
Person.hello
#=> hello, i am Person Class

Class Variables

# 如果說 instance variable 是綁定物件的資料，那 class variable
# 就是綁定 class 本身的資料
class Person  
  attr_accessor :name, :age

  # 宣告時前面加兩個 @@
  @@number_of_people = 0

  def initialize(name, age)
    @name = name
    @age = age
    # 每創一個新的 object，就會被加一次
    @@number_of_people += 1
  end

  def self.hello
    puts "hello, i am Person Class"
  end

  # 回傳 @@number_of_people
  def self.info
    @@number_of_people
  end
end

# 呼叫方式
puts Person.info
bob = Person.new("Bob", 17)
puts Person.info
# => 1
sam = Person.new("Sam", 32)
puts Person.info
# => 2

Constants

# constant 就是有些時候會遇上一些在程式裡不應改變的變數
# 像是圓周率、稅率、法定成年的年紀 etc.

class Person  
  # 宣告 constant，全部大寫
  LEGAL_AGE_TO_DRIVE = 16

  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  # 看這個人是否已到可以考駕照的年齡
  def can_drive?
    if self.age >= LEGAL_AGE_TO_DRIVE 
      puts "yes #{self.name} can drive"
    else 
      puts "no #{self.name} can't drive"
    end
  end

end

bob = Person.new("Bob", 17)
bob.can_drive?
#=> yes Bob can drive

Class Inheritance

# 我們希望在建立新的 class 時，新的 class 也包含了舊的 class 的方法和特性
# 這時就可以使用 inheritance(繼承)
# 讓我不用重新寫很多東西
class Person  
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  def greet
    puts "hello, my name is #{self.name}"
  end
end

# 使用 < 來代表繼承
class Engineer < Person

end

class Salesman < Person

end

bob = Engineer.new("Bob", 17)
sam = Salesman.new("Sam", 32)

bob.greet
sam.greet

# => hello, my name is Bob
# => hello, my name is Sam
# Engineer 和 Salesman 繼承了 Person 的 greet 方法

Super

class Person  
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  def greet
    "hello, my name is #{self.name}"
  end
end
# 如果我希望在改變 Engineer 的 greet
class Engineer < Person
  # override (覆寫) 原本 Person 的 greet
  def greet
    # super 會呼叫 parent class 裡面同樣名字的 method
    # 注意 super 只能在 method 裡面使用
    puts super + ", I know how to write Ruby"
  end
end

bob = Engineer.new("Bob", 17)
bob.greet
#=> hello, my name is Bob, I know how to write Ruby

Module

# 可把 module 想像成工具箱，本身並不是 class
# 不可 new，只能被 include 到其他 class 裡面使用
module Knowledge
  def math
    puts "I know math"
  end
end

class Person  
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  def greet
    puts "hello, my name is #{self.name}"
  end
end

class Engineer < Person
  include Knowledge
  def greet
    puts "I am an Engineer, my name is #{self.name}"
  end

end

bob = Engineer.new("Bob", 17)
bob.math
# => I know math

Method Override

class Person  
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  def greet
    puts "hello, my name is #{self.name}"
  end
end

# 如果我希望在改變 Engineer 的 greet
class Engineer < Person
  # override (覆寫) 原本 Person 的 greet
  def greet
    puts "I am an Engineer, my name is #{self.name}"
  end
end

# 創立一個叫 German 的子類別
class German < Person
  # override (覆寫) 原本 Person 的 greet
  def greet
    puts "Hallo, mein name ist #{self.name}"
  end
end

bob = Engineer.new("Bob", 17)
martin = German.new("Martin", 20)
bob.greet
martin.greet
#=> I am an Engineer, my name is Bob
#=> Hallo, mein name ist Martin

Method Lookup

class Engineer < Person
  include Knowledge
  def greet
    puts "I am an Engineer, my name is #{self.name}"
  end
end

bob = Engineer.new("Bob", 17)
bob.math
# => I know math

# 尋找 Engineer 的祖先們
puts Engineer.ancestors

# Engineer
# Knowledge
# Person
# Object
# Kernel
# BasicObject

# 一旦 object 呼叫了一個它的 Class 裡面沒有的 method
# 他就會依序找他所有的祖先，若找到了有這個 method 的祖先，就使用這個祖先類別的 method

Ruby Style Guide

http://guides.ruby.tw/ruby-rails-style-guides/

Homework 2

1. Refactor Rock Paper Scissors in      Object Oriented Style
2. 加上能上使用者輸入名字的功能，並會印出加上使用者名字的結果
3. Push to github