從 Classes 到 Objects: 那些 OOP 教我的事

從 Classes 到 Objects:
那些 OOP 教我的事
http://ihower.tw
2013/10/26@ RubyConf China

我是誰
• 張⽂文鈿 a.k.a. ihower
• http://ihower.tw
• 來⾃自台灣

Ruby Taiwan
http://ruby.tw

Agenda
•
•
•

•

OOP
class-oriented
object-oriented

•
•
•

Role-oriented
Context-oriented
DCI

Conclusion

Object = Identity
+ Behavior
+ State

Identity
a = "foo"
b = "foo"
a.object_id # 70178176631620
b.object_id # 70178176659140
a == b # true
a.equal?(b) # false

Behavior
"foo".methods =>
[:<=>, :==, :===, :eql?, :hash,
:casecmp, :+, :*, :%, :[], :
[]=, :insert, :length, :size,
:bytesize, :empty?, :=~, :match, :succ,
:succ!, :next, :next!, :upto, :index,
:rindex, :replace, :clear, :chr,
:getbyte, :setbyte, :byteslice, :to_i,
:to_f, :to_s, :to_str, :inspect, :dump,
:upcase, :downcase, :capitalize,
:swapcase, :upcase!, :downcase!,
:capitalize!, :swapcase!, :hex, :oct,

State
class Person
def name
@name
end
def name=(name)
@name = name
end
end

State (cont.)
a = Person.new
b = Person.new
a.name = "Foo"
b.name = "Bar"

class Person
attr_accessor :name
end

封裝 Encapsulation
• 物件的 State 狀態被封裝起來
• 必須透過外在的 Behavior，也就是
Method ⽅方法來存取操作

多型 Polymorphism
• Duck-typing in Ruby
• 不管物件的類型，只要有相同的介⾯面，
就可以呼叫使⽤用

class Org
attr_accessor :name
end
[Person.new, Org.new].each do |p|
puts p.name
end

Sending Message
就是呼叫物件的⽅方法

person
呼叫 name ⽅方法

內部狀態
@name

runtime picture
obj
obj

obj

obj
obj
obj

obj
obj

class-based OOP
• 物件需要⼀一種⽅方式可以⽅方便⽣生成

class-based OOP
• 絕⼤大部分的 OO 程式語⾔言都⽀支援 class-based

class-based OOP
• 是 Object 的 template 樣板

class-based OOP
• 是 Object 的 template 樣板
• 是 Object 的 factory ⼯工廠

class-oriented?
• 使⽤用 class 概念來設計整個系統

class-oriented?
• 找出系統的 nouns，以資料為中⼼心，將物
件⽤用類別進⾏行分類 (Data-centric)

class-oriented?

• 愛⽤用繼承架構

class-oriented?

• 愛⽤用繼承架構
• 最後得到系統的 static representation

Data-centric
• 例如，⼀一個 e-commerce 系統：
• Product
• Invoice
• User
• 將需要的⽅方法定義在每個類別上

A Product model
class Product
validates_presence_of :name
end

不斷加⽅方法進來
class Product
def add_to_billing(billing)
billing.items << self
end
end

A fat Product model
class Product
validates_presence_of :name, :price
def add_to_billing(order)
order.items << self
end
def tag(name)
#...
end
def self.export
#...
end
def sales_report
#...
end

你以為很多物件在互動
obj
obj

obj

obj
obj
obj

obj
obj

其實只有少數幾種物件
User

Product

Invoice

三種類型的物件
class Product
def A
def B
def C
...
...
...
...
...
end

class Invoice
def X
def Y
def Z
...
...
...
...
...
end

class User
def Q
def W
def E
...
...
...
...
...
end

最後變成
萬能的 God Object!

What’s more
Object-oriented?
如何能更善⽤用 Object?

是什麼 v.s. 做什麼
• ⼀一個物件”是什麼” (Being) 跟作什麼
(Doing) 是分開的概念


• ⼀一個物件需要有什麼⽅方法，跟當時的⾓角
⾊色和情境有關係


• ⼀一個物件需要有什麼⽅方法，跟當時的⾓角
⾊色和情境有關係

• Responsibility-centric 以職責為中⼼心，將
物件進⾏行分類

1. 根據 Roles 來區分
物件可以做什麼

def work
end
def rest
end
def approve
end
def review
end

person
Roles:
Employee

def work
end
def rest
end
def approve
end
def review
end

def work
end
def rest
end

person
Roles:
Manager

def approve
end
def review
end

Role-oriented
• 不同⾓角⾊色有不同責任，需要的⽅方法也就
不同

• ⽤用單⼀一繼承⾏行不通的，⼀一個物件可能同
時有好幾個⾓角⾊色

def buy
end
def complain
end
def approve
end
def review
end

Role:
Customer

Role:
Manager

def buy
end

person
Roles:
Customer
Manager

def complain
end
def approve
end
def review
end

Role:
Customer

Role:
Manager

怎麼實作?
We represent roles as identiﬁers ... they [roles] may
just be pointers to role-bound object, or macros, or
function or something else.
- Lean Architecture p.240

Object Composition
• ⼀一個物件裡包其他物件

Object Composition
• 靜態程式語⾔言的唯⼀一選擇

Object Composition
• 靜態程式語⾔言的唯⼀一選擇
• 眾多 Design Pattern

class Person
def initialize(role)
@role_behavior = role
end
def say
@role_behavior.say
end
end

class EmployeeRole
def say
puts "done!"
end
end
class ManagerRole
def say
puts "solid!"
end
end

Strategy Pattern!
p1 = Person.new(ManagerRole.new)
p2 = Person.new(EmployeeRole.new)

person

person

employee
role

manager
role

require 'delegate'
class Person
end
class EmployeeRole < SimpleDelegator
def say
puts "done!"
end
end
class ManagerRole < SimpleDelegator
def fly
puts "solid!"
end
end

Decorator Pattern
p1 = EmployeeRole.new(Person.new)
p2 = ManagerRole.new(Person.new)

employee

manager

person

person

Strategy v.s. Decorator
• Strategy Pattern
• 相同⽅方法，但是不同⾓角⾊色有不同演算
法時

Strategy v.s. Decorator
• Strategy Pattern
• 相同⽅方法，但是不同⾓角⾊色有不同演算
法時

• Decorator Pattern
• 當你想新增物件的⾓角⾊色⾏行為時

Object Composition
• Composition 很強⼤大
• 但是也可以搞的很複雜，特別是參數和
狀態如何在物件之間流通....

A Product model
class Product
end
end

Orderable Role
module Billingable
end
end

class Product
include Billingable
end

class Product
include
include
include
include
end

Billingable
Taggable
Exporter
Reporter

Rails4
• app/models/concerns
• app/controllers/concerns

批評
• 只是 copy-paste ⽽而已
• module 本質上還是繼承 inheritance，不
若 composition 容易替換

Poor man’s
role-oriented design
Simple, Quick and Dirty

2. 根據情境來區分
物件可以做什麼

def buy
end
def complain
end
def approve
end
def review
end

def buy
end
def complain
end
def approve
end
def review
end

購物情境
才需要

def buy
end
def complain
end
def approve
end
def review
end

客服情境
才需要

Use case
• 不同的 User case 特定情境，物件需要的
⽅方法不⼀一樣

• 例如註冊流程、購物流程

⽽而且有很多種 Patterns
• Service object
• Query object
• Form object
• View object
• Policy object
• ....根據情境分類....

Service Object
a.k.a. Command Pattern
包裝跨 Data Model 的操作

class BillingControllers < ApplicationController
before_filter :find_current_billing
def add_product
@product = Product.find(params[:product_id])
BillingService.new(@billing, @product).perform!
end
end

Service Object
class BillingService
def initialize(billling, product)
@billling = billling
@product = product
end
def perform!
add_product_to_billling(@billling, @product)
end
private
def add_product_to_billling(billling, product)
billling.items << product
end
end

Query Object
包裝複雜的 SQL 查詢

class ProductQuery
def initialize(relation = Product.scoped)
@relation = relation
end
def by_regions(region_ids = nil)
if region_ids.present?
countrys = RegionCountry.where(:region_id =>
region_ids).pluck(:country_alpha2)
@relation = @relation.where(:country => countrys)
end
self
end
end
@products = ProductQuery.new.by_regions(region_ids)

View Object
包裹給 Rails View 使⽤用

class DashboardView
def initialize(company)
@company = company
end
def arr
#...
end
def mrr
#...
end
def cac
#...
end
end

Form Object
搭配 Rails 的表單

class Signup
include Virtus
extend ActiveModel::Naming
include ActiveModel::Conversion
include ActiveModel::Validations
attr_reader :user
attr_reader :company
attribute :name, String
attribute :company_name, String
attribute :email, String
validates :email, presence: true
# … more validations …
# Forms are never themselves persisted
def persisted?
false
end
def save
if valid?
persist!
true
else
false
end
end

class SignupsController < ApplicationController
def create
@signup = Signup.new(params[:signup])
if @signup.save
redirect_to dashboard_path
else
render "new"
end
end
end

增加物件的多樣性
避免肥⼤大的類別
obj
obj

obj

obj
obj
obj

obj
obj

DCI
⾓角⾊色+情境
將 Behavior 跟 Data model 分開的更徹底

DCI
• Data: 資料
• 例如 Product

DCI
• Data: 資料
• 例如 Product
• Context: 情境

DCI
• Data: 資料
• 例如 Product
• Context: 情境
• 例如加⼊入購物⾞車這個 Use case

DCI
• Data: 資料
• 例如 Product
• Context: 情境
• Interaction: ⾏行為

DCI
• Data: 資料
• 例如 Product
• Context: 情境
• Interaction: ⾏行為
• 例如加⼊入購物⾞車這個⽅方法

呼叫⽅方式
class BillingControllers < ApplicationController
before_filter :find_current_billing
def add_product
@product = Product.find(params[:product_id])
BillingContext.new(@billing, @product).perform!
end
end

情境
class BillingContext
end
def perform!
@product.add_to_billling(@billling)
end
end

class Product < ActiveRecord::Base
# 注意，這裡不放 Behavior 了
end

Billingable Role
module Billlingable
def add_to_billling(billling)
billling.items << self
end
end
end

@product.extend(Billingable)
end
def perform!
end
module Billlingable
billling.items << self
end
end

data model 的 behavior，
是 run-time 的時候，根據當時的需要
動態 extend 進去物件

compile-time
Product
class
沒有⾏行為

run-time
extend ⾏行為模組

Product
object
加上⾏行為

⽤用 Wrapper ?
require 'delegate'
@product = BillingableProduct.new(product)
end
def perform!
end
class BilllingableProduct < SimpleDelegator
billling.items << __getobj__
end
end
end

self 精神分裂
http://en.wikipedia.org/wiki/Schizophrenia_(object-oriented_programming)

• __getobj__
• 多包⼀一層，物件的 identify 和 class 是不⼀一
樣的，需要處理資料傳遞和分享的問題

• 就算⾃自⼰己寫 Wrapper，也很⿇麻煩
• 更別提如果有兩個以上的 Roles

Benchmark
並沒有數量級的差距
0.4
0.3
0.2
0.1
0

inherited

mixin

wrapper

simple delegator

extend(DCI)

https://gist.github.com/ihower/7160400

結論
• 從 Data-Centric 到 Responsibility-centric

結論
• 從 Data-Centric 到 Responsibility-centric
• 物件的 Behavior 會因為⾓角⾊色和情境⽽而需求不

同，可以分開。⽽而不需要通通塞在 data model
上

結論 (cont.)
•

在靜態語⾔言中，Composition 是唯⼀一解

結論 (cont.)
•
•

但是在 Ruby 中，善⽤用⼀一些技巧可以事半功倍

•
•

Mixins
DCI

結論 (cont.)
•
•
•

但是在 Ruby 中，善⽤用⼀一些技巧可以事半功倍

•
•

Mixins
DCI

因為 Ruby 把 class 當作 behavior 的容器，⽽而
不是死的 template，所以可以動態地修改⾏行
為

Reference:
•
•
•

Object-Oriented Programming: Objects over Classes (The ThoughtWorks Anthology 2)

•
•
•
•
•

http://mikepackdev.com/blog_posts/24-the-right-way-to-code-dci-in-ruby

•

http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecordmodels/

•

https://speakerdeck.com/stefanoverna/fat-models-must-die

Clean Ruby, Jim Gay
Rails Developers Should Take DCI Seriously http://gilesbowkett.blogspot.tw/2012/12/
rails-developers-should-take-dci.html
http://dci-in-ruby.info/
https://practicingruby.com/articles/responsibility-centric-vs-data-centric-design
http://37signals.com/svn/posts/3372-put-chubby-models-on-a-diet-with-concerns
http://blog.gemnasium.com/post/60091511603/casting-adding-behavior-to-objectswithout-using

謝謝！
歡迎參加明晚 Faria Systems 的
After Party

從 Classes 到 Objects: 那些 OOP 教我的事

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