Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Why Every Element of SOLID is Wrong
Search
Daniel Terhorst-North
PRO
January 20, 2017
Technology
130
110k
Why Every Element of SOLID is Wrong
Five minute Ignite-style talk from PubConf London 2016
Daniel Terhorst-North
PRO
January 20, 2017
Tweet
Share
More Decks by Daniel Terhorst-North
See All by Daniel Terhorst-North
20 Years of BDD
tastapod
PRO
0
54
The best programmer I know
tastapod
PRO
2
320
How to bake a change
tastapod
PRO
0
510
The Most Dangerous Phrase
tastapod
PRO
7
6.2k
Rethinking Transformation
tastapod
PRO
1
410
CUPID - for joyful coding
tastapod
PRO
5
7.5k
agility at scale - a meeting of mindsets
tastapod
PRO
1
590
SWARMing into action
tastapod
PRO
0
390
Deliberate Advice
tastapod
PRO
3
1.5k
Other Decks in Technology
See All in Technology
AIの全社活用を推進するための安全なレールを敷いた話
shoheimitani
2
640
Operating Operator
shhnjk
1
650
公開初日に Gemini CLI を試した話や FFmpeg と組み合わせてみた話など / Gemini CLI 初学者勉強会(#AI道場)
you
PRO
0
1k
セキュアな社内Dify運用と外部連携の両立 ~AIによるAPIリスク評価~
zozotech
PRO
0
100
IPA&AWSダブル全冠が明かす、人生を変えた勉強法のすべて
iwamot
PRO
2
220
第64回コンピュータビジョン勉強会「The PanAf-FGBG Dataset: Understanding the Impact of Backgrounds in Wildlife Behaviour Recognition」
x_ttyszk
0
170
Amplify Gen2から知るAWS CDK Toolkit Libraryの使い方/How to use the AWS CDK Toolkit Library as known from Amplify Gen2
fossamagna
0
230
助けて! XからWaylandに移行しないと新しいGNOMEが使えなくなっちゃう 2025-07-12
nobutomurata
2
140
データ基盤からデータベースまで?広がるユースケースのDatabricksについて教えるよ!
akuwano
3
160
SREのためのeBPF活用ステップアップガイド
egmc
1
870
shake-upを科学する
rsakata
7
920
LLM時代の検索
shibuiwilliam
2
640
Featured
See All Featured
The Myth of the Modular Monolith - Day 2 Keynote - Rails World 2024
eileencodes
26
2.9k
Designing for humans not robots
tammielis
253
25k
Speed Design
sergeychernyshev
32
1k
Done Done
chrislema
184
16k
A better future with KSS
kneath
238
17k
The World Runs on Bad Software
bkeepers
PRO
69
11k
Optimising Largest Contentful Paint
csswizardry
37
3.3k
10 Git Anti Patterns You Should be Aware of
lemiorhan
PRO
656
60k
How STYLIGHT went responsive
nonsquared
100
5.6k
The MySQL Ecosystem @ GitHub 2015
samlambert
251
13k
Visualization
eitanlees
146
16k
Site-Speed That Sticks
csswizardry
10
700
Transcript
Why Every Single Element of SOLID is Wrong! Dan North
@tastapod
Single Responsibility Open/Closed Liskov Substitution Interface Segregation Dependency Inversion
Single Responsibility Principle “one reason to change” “only do one
thing”
Single Responsibility Principle What is a single responsibility anyway? ETL:
three responsibilities or one? How can you predict what is going to change? Pointlessly Vague Principle
Single Responsibility Principle Simple code is easy to reason about
Can easily do several related things Refactor until it Fits In Your Head Write simple code
Open-Closed Principle Open for extension, closed for modification “When requirements
change, extend behaviour by adding new code, not changing code that works”
Open-Closed Principle Open for extension, closed for modification “When requirements
change, the existing code is now wrong! so replace it with code that works” Cruft Accretion Principle
Open-Closed Principle Simple code is easy to change Simple code
is easy to test Simple code is both open and closed Write simple code!
Liskov Substitution Principle “Strong behavioural subtyping” Substitution with a subtype
preserves all “desirable properties” of the original type “Provably undecidable” but useful
Liskov Substitution Principle “There is nothing quite so useless, as
doing with great efficiency, something that should not be done at all.” Stuck in is-a and has-a modelling mindset Drucker’s Warning Principle
Liskov Substitution Principle What about acts-like-a, can-be-used-as-a? Composition is simpler
than inheritance Try to avoid object hierarchies altogether Write simple code!
Interface Segregation Principle Many small interfaces are better than one
big object Design small, role-based interfaces No client depends on methods it doesn’t use
Interface Segregation Principle Practically anything is better than one big
object Design small, role-based classes No client depends on methods it doesn’t use Stable Door Principle This is already true!! —>
Interface Segregation Principle Don’t write big objects in the first
place! Write code that Fits In Your Head If a class needs lots of interfaces, simplify the class! Write simple code!
Dependency Inversion Principle High-level modules should not depend on lower-level
modules Abstractions (e.g. interfaces) should not depend on details (e.g. concrete implementations)
Dependency Inversion Principle Reuse is overrated, design for use! DIP
leads to a different kind of dependency, dependency on DI frameworks! Wrong Goal Principle
Dependency Inversion Principle See how far you get combining simple
classes new is the new new! Assemble into small components that Fit In Your Head Write simple code!
Single Responsibility Open/Closed Liskov Substitution Interface Segregation Dependency Inversion
Single Responsibility Open/Closed Liskov Substitution Interface Segregation Dependency Inversion Too
much to remember!
Single Responsibility Open/Closed Liskov Substitution Interface Segregation Dependency Inversion Write
simple code!