漫談重構

Teddy Chen
teddy@teddysoft.tw
http://teddy-chen-tw.blogspot.tw/
2020/09/15

• Part 1: 什麼是重構？
• Part 2: 從定義看重構
• Part 3: 重構的定位
– Refactoring and Patterns
• Part 4: 重構與設計方法
– TDD/BDD/SBE vs OOAD vs DDD
• Part 5: 重構範例討論
Copyright@2020 Teddysoft

在不改變程式外在行為的前提之下，
改變程式內部結構以提升設計品質的方法
Before refactoring After refactoring

http://goo.gl/6uqzes
B
A

《Extreme Programming explained》
好的軟體設計，其改變的成本應該與改變的範圍有關，
與改變發生的時間點無關《Clean Architecture》

Copyright@2012-2016 Teddysoft Source http://goo.gl/roc09w

• Refactoring (Noun )
– A change made to the internal structure of
software to make it easier to understand and
cheaper to modify without changing its observable
behavior. (對軟體內部結構的一種改變，目的在不改動軟體可察覺行
為的前提之下，提高其可理解性並降低修改成本。)
• Refactor (Verb)
– To restructure software by applying a series of
refactoring without changing its observable
behavior. (在不改變軟體可察覺行為的前提之下使用一系列重構方法
調整軟體結構。)
Copyright@2020 Teddysoft Source:《Refactoring》

Copyright@2020 Teddysoft Source:《Refactoring》

確定所有測試
都通過
發現怪味道決定如何簡化
簡化程式
(重構)
確定所有測試
都依舊通過

• 隨時
• 事不過三原則
• 當增加新功能很困難時
• 當你對程式更了解時
• 當你修正bug時
• 當程式碼發臭時

• 沒有測試案例
• 測試案例失敗時
• 當你應該重寫而非重構時
• 當你的截止日期迫在眉睫時

• Shared code
• Coding standards
• Pair programming
• Simple design
– Passes the tests, Reveals intention, No duplication,
Fewest elements
• Tests
• Continuous integration
• Rested programmers
Copyright@2020 Teddysoft 《Extreme Programming Explained》

Source:《Refactoring》

Data Class
Feature Envy

5
2
4
改變程式內部結構以提升設計品質
1
6
如何確認? 如何定義?
怎麼改? 哪些結構可以改? 品質的提升目標為何?
3 為什麼要以不改變程
式外在行為當作前提?

1

if 1 == 1 then S1 else S2
開什麼玩笑!
太難
Ref. : https://goo.gl/sBYyAg
• Denotational semantics
• Operational semantics
• Axiomatic semantics

• Normal behavior
– 一般重構
• Exceptional behavior
– 例外處理重構

Replace semantics proven
with scenario-based tests

思考問題1：
用測試定義行為有何優缺點？
有無替代方案？

2

• 使用工具
– 編譯器
– 重構工具
• 執行測試案例
– Local Build
– CI Build
IntelliJ 的重構選項

• Normal behavior
– 一般重構
– 不改變程式的正常行為
• Exceptional behavior
– 例外處理重構
– 可能會改變程式的例外行為

重構最常用執行測試驗
證程式行為有無改變

3

• 開發的兩頂帽子
– 實作功能性需求 (do the right thing)
– 改善設計（do the thing right; 寫出clean code）
• 呼應軟體設計原則
– Separation of Concerns
– Single Responsibility Principle
– One Pattern at a Time

思考do the thing right
的時候不要管do the
right thing

4

Package
Class
Method
Block
Statement
Variable
作用在不同結構上的重構，
產生不同層次的設計改善
Common program
constructs to be
coded & refactored
• Rename
• Introduce Assertion
• Extract Method
• Move Method
• Extract Class
• Form Template Method
• Separate Domain from Presentation

程式結構有大有小，
重構亦然

5

• Dispensable
– Comments, Duplicated Code, Lazy Class, Data Class, Speculative
Generality
• Bloater
– Long Method, Long Parameter List, Large Class, Data Clumps,
Primitive Obsession
• OO Abuser
– Switch Statement Repeated Switches, Temporary Field, Alternative
Classes with Different Interfaces, Refused Bequest
• Coupler
– Feature Envy, Message Chains, Middle Man, Inappropriate Intimacy,
Incomplete Library Class
• Change Preventer
– Divergent Change, Shotgun Surgery, Parallel Inheritance Hierarchies

Parameter Object

6

A change made to the internal structure
of software to make it easier to
understand and cheaper to modify
without changing its observable behavior.
較易理解，較低修改成本

Understandability
Modifiability
Low Coupling
High Cohesion
OO Concept
OO Principle
Design Pattern
Architecture
⚫ Abstraction
⚫ Information hiding
⚫ Polymorphism
⚫ Responsibility
assignment
⚫ Indirection
⚫ Separation of concerns
⚫ Program to an interface,
not an implementation
⚫ Favor object composition
over class inheritance
⚫ Single-responsibility
⚫ Open-closed
⚫ Liskov substitution
⚫ Interface-segregation
⚫ Dependency-inversion
⚫ Don't repeat yourself,
Single choice, One and
only once

重構有大有小，
重構目標亦然

民意調查：
重構是一種模式（Pattern）嗎？

• 設計模式
– Singleton, Command, Proxy, Adapter, Model-
View-Controller, etc.
• 重構
– Rename, Introduce Assertion, Extract
Method, Move Method, Extract Class, Form
Template Method, Separate Domain from
Presentation, etc.

• 名詞片語 (Noun-phrase)
– 描述模式所建立或產生的結果
– 例子：Singleton, Command, Model-View-
Controller
• 動詞片語 (Verb-phrase)
– 給定一個指令，描述如何達到模式解決方案所要
求的狀態
– 例子：Don’t Talk to Strangers, Separate
Material Preparation from Integration

Copyright@2020 Teddysoft Source:《The Timeless Way of Building》
http://goo.gl/tS13cE

思考問題2：
如果重構是一種模式，為什麼重構用動詞而
不像大部份設計模式採用名詞？
Rename VS Intention Revealing Names

• Make you instant expert
• Eliminate the need for intelligence and
taste
• Eliminate the need to think
• Tell you how exactly how to adapt the
solution to your context
Source: Asian PLoP 2016 by Joseph
Yoder and Rebecca Wirfs-Brock

重構相反重構
Extract Method Inline Method
Add Parameter Remove Parameter
Collapse Hierarchy Extract Superclass, Extract Subclass
Extract Class Inline Class
Hide Delegate Remove Middle Man
Pull Up Field Push Down Field
Replace Inheritance with Delegation Replace Delegation with Inheritance

Copyright@2020 Teddysoft Source: 電影《星際大戰第四集》

設計就是決定Context與Form的邊界
Source:《Notes on the Synthesis of Form》
Context
Before
MachineProblem
force
force
Worl
d
Resulting
Context
Solution
force
force
force
After
force

重構是一種模式，
套用模式要觀察
Context與Forces

Top-down
Bottom-up

• OOAD (傳統模式)
– Code-First
– Top-down
• TDD (原始模式)
– Test-First
– Bottom-up

Domain Model
Design Model
Implementation
Model
Refactoring
After
ImplementationUse Case
Model

Design Model
Implementation
Model
After
Implementation
Refactoring
Test & Code
OOAD
TDD
Domain Model
Use Case
Model
Most design
happens here
Refactoring
https://goo.gl/8AZQUQ

https://goo.gl/8AZQUQ

Design Model
Implementation
Model
After
Implementation
Refactoring
Test & Code
OOAD
BDD/SBE + TDD
Test cases as
specification
Domain Model
Use Case
Model
Most design
happens here
Refactoring

Design Model
Implementation
Model
After
Implementation
Refactoring
Test & Code
OOAD
TDD
Test cases as
specification
Domain Model
Use Case
Model
Domain Model
DDD can help.
Design happens here
And design
happens here
Refactoring

思考問題3：
DDD+BDD/SBE+TDD之後，傳統bottom-
up形式的test-first開發，還算是bottom-
up嗎？

Source:《禪的世界01--冥想》

部分的加總不等於
全部，體驗整體的
感覺有其必要性

CreateBoardController CreateBoardUseCase
Board
BoardRepository
Middle Man?

CreateBoardController CreateBoardUseCase
Board
BoardRepository
Middle Man?
《Clean Architecture》

All problems in computer
science can be solved by
another level of indirection
by David Wheeler

public record Person (String name, String address) {}

Package by Layer Package by Feature

1. Card
2. Work Item
3. Task
4. Ticket
哪個名字好?

• 程式結構有大有小，重構亦然。
• 重構是一種模式，套用模式要觀察Context
與Forces。
• 設計是一種由上而下的過程，部分的加總不
等於全部，先體驗整體的感覺有其必要性。
– 事後諸葛亮，事前豬一樣 VS 事前諸葛亮

• 搞笑談軟工部落格
– http://teddy-chen-tw.blogspot.com
• 搞笑談軟工Facebook
– https://www.facebook.com/groups/teddy.tw
• 泰迪軟體官方網站
– http://teddysoft.tw

漫談重構

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