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
extremely defensive coding - rubyconf edition
Search
Penelope Phippen
November 16, 2015
Technology
0
260
extremely defensive coding - rubyconf edition
Penelope Phippen
November 16, 2015
Tweet
Share
More Decks by Penelope Phippen
See All by Penelope Phippen
Introducing Rubyfmt
penelope_zone
0
560
How RSpec Works
penelope_zone
0
6.6k
Quick and easy browser testing using RSpec and Rails 5.1
penelope_zone
1
82
Teaching RSpec to play nice with Rails
penelope_zone
2
130
Little machines that eat strings
penelope_zone
1
99
What is processor (brighton ruby edition)
penelope_zone
0
110
What is processor?
penelope_zone
1
350
Agile, etc.
penelope_zone
2
220
Extremely Defensive Coding
penelope_zone
0
94
Other Decks in Technology
See All in Technology
Tech-Verse 2025 Keynote
lycorptech_jp
PRO
0
1.7k
AWS認定を取る中で感じたこと
siromi
1
160
KubeCon + CloudNativeCon Japan 2025 Recap Opening & Choose Your Own Adventureシリーズまとめ
mmmatsuda
0
260
Flutter向けPDFビューア、pdfrxのpdfium WASM対応について
espresso3389
0
120
作曲家がボカロを使うようにPdMはAIを使え
itotaxi
0
430
Lazy application authentication with Tailscale
bluehatbrit
0
150
20250705 Headlamp: 專注可擴展性的 Kubernetes 用戶界面
pichuang
0
180
論文紹介:LLMDet (CVPR2025 Highlight)
tattaka
0
290
ドメイン特化なCLIPモデルとデータセットの紹介
tattaka
2
570
OPENLOGI Company Profile
hr01
0
67k
KubeCon + CloudNativeCon Japan 2025 Recap by CA
ponkio_o
PRO
0
290
OPENLOGI Company Profile for engineer
hr01
1
33k
Featured
See All Featured
Refactoring Trust on Your Teams (GOTO; Chicago 2020)
rmw
34
3.1k
Facilitating Awesome Meetings
lara
54
6.4k
Building Flexible Design Systems
yeseniaperezcruz
328
39k
Six Lessons from altMBA
skipperchong
28
3.9k
Dealing with People You Can't Stand - Big Design 2015
cassininazir
367
26k
Imperfection Machines: The Place of Print at Facebook
scottboms
267
13k
Save Time (by Creating Custom Rails Generators)
garrettdimon
PRO
31
1.3k
The Psychology of Web Performance [Beyond Tellerrand 2023]
tammyeverts
48
2.9k
How to Think Like a Performance Engineer
csswizardry
24
1.7k
Exploring the Power of Turbo Streams & Action Cable | RailsConf2023
kevinliebholz
34
5.9k
Java REST API Framework Comparison - PWX 2021
mraible
31
8.7k
Helping Users Find Their Own Way: Creating Modern Search Experiences
danielanewman
29
2.7k
Transcript
Extremely Defensive Coding
a!/samphippen
Who is having fun?
Who is here for their first time?
I want to start with a story
“When is it OK to override the methods on object?”
I umm’d and ahh’d for a bit
I gave a half explanation and then asked them if
they understood
I eventually came to an answer to do with consistency
Do it when it makes your object more consistent with
Ruby, not less
e.g. an == on a data object
What makes a gem good?
Internals?
Internals?
Interface?
Interface? ✅
More convenient than if I did it myself
And it stays convenient
And it can be used by everyone on a team
And it works with a wide range of Ruby codebases
RSpec
RSpec Definitely always convenient
RSpec Definitely always convenient
User story
As an RSpec user
When I stub an object
I want the original method to be on that object
after the example
So that my objects aren’t broken by my test suite
As an RSpec user
When I stub an object
I want the original method to be on that object
after the example
So that my objects aren’t broken by my test suite
How does that work?
allow(cat).to receive(:meow)
Takes the meow method off cat
Saves it
Executes test
Puts the method back on the original object
How do you save a method?
None
Method object
Put it somewhere else
Put it back at end of test
The end
The end
Defensive coding
RSpec::Support .method_handle_for
Simply invoking the method method is not good enough
Some scenes may have been altered/accelerated for your viewing pleasure
Let’s have some questions !/samphippen
[email protected]
Users Lie
def method ‘get’ end
Users can redefine anything at any time in Ruby
and that’s fine
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Instance method object Method without a target object
Comes from a class/module not an instance
Grab the Kernel implementation of #method
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Users can and will redefine core methods at any time
Instead we use Kernel’s implementation
Nobody screws with Kernel
Ruby interpreters lie
Some objects do not have Kernel in their inheritance chain
None
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Rebinding module methods
c
c
RSpec does not support Rubinius
None
We tried, we really really tried
So anyway, dealing with module methods
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Ruby interpreters behave differently.
Let’s have some questions !/samphippen
[email protected]
Sometimes users don’t lie
None
None
None
None
`method': undefined method `foo' for class `Foo' (NameError)
This is a catch 22
Solution: trust but verify
None
None
None
Let’s put it all together
None
Wrapping up
This is why I love RSpec
Please file bugs
Your gem should be defensive
Users lie Redefinitions come from anywhere, expect them
Ruby interpreters lie Your code will run on non-MRI, old
MRI, etc
Sometimes users don’t lie Users are weird, trust but verify
What makes a gem good?
Internals?
That explanation made no sense
Internals?
Interface?
allow(cat).to receive(:meow)
You get the complexity of RSpec working with any object
for free
You probably didn’t even know it was there until I
just told you
Interface? ✅
Gems
Gems provide strong abstraction boundaries
Done badly they cause an even more extreme mess
Done correctly they hide huge complexity behind well defined barriers
Defending against users helps your gem be convenient
Write defensively, and your users will never know what’s inside
the box
Remember the story?
This talk is born out of Ruby’s power
We need our code to defend today, against the mistakes
of our tomorrow
Let’s have some questions !/samphippen
[email protected]
Let’s have some questions !/samphippen
[email protected]
Minitest Mock is 169 lines of code
I just showed you more code than that
For a tiny feature that isn’t a complete mocking library
and that’s fine
Please check out https://browserpath.co
None
Let’s have some questions a!/samphippen
[email protected]