Ruby bits (class 篇)


Outline
  1. 1. 目錄 (class 篇)
  2. 2. 1. Scope $: global、@@: class、@: instance
  3. 3. 2. attr_accessor (getter & setter)
    1. 3.1. same as
    2. 3.2. attr_reader、attr_writer、self
  4. 4. 3. private（cannot be called with explicit receiver）
    1. 4.1. protected （可被 class 內呼叫）
  5. 5. 4. Inheritance（ Override、super）
  6. 6. 5. ACTIVESUPPORT
  7. 7. 6. Struct
  8. 8. 7. Send（可以呼叫 private or protected method）
  9. 9. 8. method （放在記憶體，等等再 .call ）

目錄 (class 篇)

  1. Scope
  2. attr_accessor、attr_reader、self
  3. private、protected
  4. Inheritance
  5. ACTIVESUPPORT
  6. Struct
  7. Send
  8. method

1. Scope $: global、@@: class、@: instance

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class Computer 
  $manufacturer = "Mango Computer, Inc."  # global variable
  @@files = {hello: "Hello, world!"}      # class variable
  
  def initialize(username, password)
    @username = username                  # instance variable
    @password = password
  end
  
  def current_user
    @username
  end
  
  def self.display_files                  # class method
    @@files
  end
end
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hal = Computer.new("Dave", 12345)
puts "Current user: #{hal.current_user}" #=> Current user: Dave
puts "Manufacturer: #{$manufacturer}"    #=> Manufacturer: Mango Computer, Inc.
puts "Files: #{Computer.display_files}"  #=> Files: {:hello=>"Hello, world!"}

2. attr_accessor (getter & setter)

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attr_accessor :baz

same as

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def baz=(value)
  @baz = value
end
def baz
  @baz
end

attr_reader、attr_writer、self

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class Tweet
  attr_accessor :status
  attr_reader :created_at   # 沒有setter
  def initialize(status)
    self.status = status    # 或 @status = status
    @created_at = Time.new  # 不能 self.created_at
  end
end

self: the current object，需要 setter。 

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class Person
  attr_reader :name           # getting
  attr_writer :job            # changing
  def initialize(name, job)
    @name = name
    @job = job
  end
end
  • attr_reader + attr_writer = attr_accessor

3. private（cannot be called with explicit receiver）

  • 預設是 public
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class User
  def up_vote(friend)
    bump_karma         # 能呼叫
    friend.bump_karma  # 不能呼叫（外來物件）
  end
  private
  def bump_karma
    puts "karma up for #{name}"
  end
end

protected （可被 class 內呼叫）

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class User
  def up_vote(friend)
    bump_karma         # 能呼叫
    friend.bump_karma  # 能呼叫
  end
  protected
  def bump_karma
    puts "karma up for #{name}"
  end
end

4. Inheritance（ Override、super）

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class Creature
  def initialize(name)
    @name = name
  end
  
  def fight
    return "B"
  end
end
class Dragon < Creature
  def fight                   # Override
    puts "A" 
    super                     # super         
  end  
end
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=> 
A
B

5. ACTIVESUPPORT

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# install
$ gem install activesupport
$ gem install i18n

# load it
require 'active_support/all'

6. Struct

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class Tweet
  attr_accessor :user, :status
  def initialize(user, status)
    @user, @status = user, status
  end 
  def to_s
    "#{user}: #{status}"
  end
end

等價於

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Tweet = Struct.new(:user, :status) do 
  def to_s
    "#{user}: #{status}"
  end
end

7. Send（可以呼叫 private or protected method）

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class Timeline
  def initialize(tweets)
    @tweets = tweets
  end
  def contents
    @tweets
  end 
  private
  def direct_messages
  end 
end
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tweets = ['Compiling!', 'Bundling...']
timeline = Timeline.new(tweets)
timeline.contents
等價於
timeline.send(:contents)
等價於
timeline.send("contents")
timeline.send(:direct_messages)  # call private

8. method （放在記憶體，等等再 .call ）

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class Timeline
  def initialize(tweets)
    @tweets = tweets
  end
  def contents
    @tweets
  end
end
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content_method = timeline.method(:contents)
#=> #<Method: Timeline#contents>
content_method.call
#=> ["Compiling!", "Bundling..."]
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