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https://github.com/leo424y/clean-code-ruby

單一職責

Bad:

class UserSettings
  def initialize(user)
    @user = user
  end

  def change_settings(settings)
    return unless valid_credentials?
    # ...
  end

  def valid_credentials?
    # ...
  end
end

Good:

class UserAuth
  def initialize(user)
    @user = user
  end

  def valid_credentials?
    # ...
  end
end

class UserSettings
  def initialize(user)
    @user = user
    @auth = UserAuth.new(user)
  end

  def change_settings(settings)
    return unless @auth.valid_credentials?
    # ...
  end
end

開放封閉原則

便於擴充

Bad:

class Adapter
  attr_reader :name
end

class AjaxAdapter < Adapter
  def initialize
    super()
    @name = 'ajaxAdapter'
  end
end

class NodeAdapter < Adapter
  def initialize
    super()
    @name = 'nodeAdapter'
  end
end

class HttpRequester
  def initialize(adapter)
    @adapter = adapter
  end

  def fetch(url)
    adapter_name = @adapter.name

    if adapter_name == 'ajaxAdapter'
      make_ajax_call(url)
    elsif adapter_name == 'httpNodeAdapter'
      make_http_call(url)
    end
  end

  def make_ajax_call(url)
    # ...
  end

  def make_http_call(url)
    # ...
  end
end

Good:

class Adapter
  attr_reader :name
end

class AjaxAdapter < Adapter
  def initialize
    super()
    @name = 'ajaxAdapter'
  end

  def request(url)
    # ...
  end
end

class NodeAdapter < Adapter
  def initialize
    super()
    @name = 'nodeAdapter'
  end

  def request(url)
    # ...
  end
end

class HttpRequester
  def initialize(adapter)
    @adapter = adapter
  end

  def fetch(url)
    @adapter.request(url)
  end
end

LSP

Bad:

class Rectangle
  def initialize
    @width = 0
    @height = 0
  end

  def color=(color)
    # ...
  end

  def render(area)
    # ...
  end

  def width=(width)
    @width = width
  end

  def height=(height)
    @height = height
  end

  def area
    @width * @height
  end
end

class Square < Rectangle
  def width=(width)
    @width = width
    @height = width
  end

  def height=(height)
    @width = height
    @height = height
  end
end

def render_large_rectangles(rectangles)
  rectangles.each do |rectangle|
    rectangle.width = 4
    rectangle.height = 5
    area = rectangle.area # BAD: Returns 25 for Square. Should be 20.
    rectangle.render(area)
  end
end

rectangles = [Rectangle.new, Rectangle.new, Square.new]
render_large_rectangles(rectangles)

Good:

class Shape
  def color=(color)
    # ...
  end

  def render(area)
    # ...
  end
end

class Rectangle < Shape
  def initialize(width, height)
    super()
    @width = width
    @height = height
  end

  def area
    @width * @height
  end
end

class Square < Shape
  def initialize(length)
    super()
    @length = length
  end

  def area
    @length * @length
  end
end

def render_large_shapes(shapes)
  shapes.each do |shape|
    area = shape.area
    shape.render(area)
  end
end

shapes = [Rectangle.new(4, 5), Rectangle.new(4, 5), Square.new(5)]
render_large_shapes(shapes)

Liskov Substitution Principle (LSP)

Bad:

class Rectangle
  def initialize
    @width = 0
    @height = 0
  end

  def color=(color)
    # ...
  end

  def render(area)
    # ...
  end

  def width=(width)
    @width = width
  end

  def height=(height)
    @height = height
  end

  def area
    @width * @height
  end
end

class Square < Rectangle
  def width=(width)
    @width = width
    @height = width
  end

  def height=(height)
    @width = height
    @height = height
  end
end

def render_large_rectangles(rectangles)
  rectangles.each do |rectangle|
    rectangle.width = 4
    rectangle.height = 5
    area = rectangle.area # BAD: Returns 25 for Square. Should be 20.
    rectangle.render(area)
  end
end

rectangles = [Rectangle.new, Rectangle.new, Square.new]
render_large_rectangles(rectangles)

Good:

class Shape
  def color=(color)
    # ...
  end

  def render(area)
    # ...
  end
end

class Rectangle < Shape
  def initialize(width, height)
    super()
    @width = width
    @height = height
  end

  def area
    @width * @height
  end
end

class Square < Shape
  def initialize(length)
    super()
    @length = length
  end

  def area
    @length * @length
  end
end

def render_large_shapes(shapes)
  shapes.each do |shape|
    area = shape.area
    shape.render(area)
  end
end

shapes = [Rectangle.new(4, 5), Rectangle.new(4, 5), Square.new(5)]
render_large_shapes(shapes)

Interface Segregation Principle (ISP)

Bad:

class Car
  # used by Driver
  def open
    # ...
  end

  # used by Driver
  def start_engine
    # ...
  end

  # used by Mechanic
  def change_engine
    # ...
  end
end

class Driver
  def drive
    @car.open
    @car.start_engine
  end
end

class Mechanic
  def do_stuff
    @car.change_engine
  end
end

Good:

# used by Driver only
class Car
  def open
    # ...
  end

  def start_engine
    # ...
  end
end

# used by Mechanic only
class CarInternals
  def change_engine
    # ...
  end
end

class Driver
  def drive
    @car.open
    @car.start_engine
  end
end

class Mechanic
  def do_stuff
    @car_internals.change_engine
  end
end

Dependency Inversion Principle (DIP)

Bad:

class InventoryRequester
  def initialize
    @req_methods = ['HTTP']
  end

  def request_item(item)
    # ...
  end
end

class InventoryTracker
  def initialize(items)
    @items = items

    # BAD: We have created a dependency on a specific request implementation.
    @requester = InventoryRequester.new
  end

  def request_items
    @items.each do |item|
      @requester.request_item(item)
    end
  end
end

inventory_tracker = InventoryTracker.new(['apples', 'bananas'])
inventory_tracker.request_items

Good:

class InventoryTracker
  def initialize(items, requester)
    @items = items
    @requester = requester
  end

  def request_items
    @items.each do |item|
      @requester.request_item(item)
    end
  end
end

class InventoryRequesterV1
  def initialize
    @req_methods = ['HTTP']
  end

  def request_item(item)
    # ...
  end
end

class InventoryRequesterV2
  def initialize
    @req_methods = ['WS']
  end

  def request_item(item)
    # ...
  end
end

# By constructing our dependencies externally and injecting them, we can easily
# substitute our request module for a fancy new one that uses WebSockets.
inventory_tracker = InventoryTracker.new(['apples', 'bananas'], InventoryRequesterV2.new)
inventory_tracker.request_items