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My five mantras to
write better Software
Raúl Ávila
Mantra
• “a sound, word, or phrase that is repeated by
someone who is praying or meditating
• “a word or phrase that is repeated often or that
expresses someone’s basic beliefs”
(Merrian-Webster)
Two questions
We have to pay maximum
attention to our code
Improving the way we write
code
1. Pair programming
2. Code reviews
3. Reading books
• Embrace main ideas as mantras
• Apply them consistently
• On a daily basis
1
Broken window theory
• “When a community tolerates minor examples of
disorder (…) such as broken windows (…) people
are more likely to commit more serious crimes”
Source: http://bit.ly/2ebQEgR
1. “Don’t leave broken
windows”
As soon as you see a broken
window…fix it!
But we have to deliver!
Two levels
1. Stop the world!
2. Next iteration
Examples
Inconsistent naming conventions
TODO comments
Unclear code formatting style
Commented out code
• Dead code
• Unused imports
• Ignored tests
• Unused dependencies
• Several dependencies to do the same
thing
• No README file
• Unclear Git strategy
• Manual steps in deployments
• Unstable CI
Delivery practices
2
2. “Extract till you drop”
Short term memory
Between 5 and 9 items
Extract variables
Extract functions
Benefits
• Extracting increases readability
• Indentation is reduced drastically
• Makes responsibilities arise
• Avoids big balls of mud
• Facilitates benchmarking
Not extracting
Extract classes
• When a function is hard to split (i.e. it has many
parameters)…maybe it should be a class
• Or maybe two classes!
• More on this later
Extract packages
3
3. “Do one thing, do it
well, and do it only”
(Single Responsibility Principle)
What is (or what defines) a
responsibility?
It depends…
Functions
1. Its name describes accurately what it does
2. Such name does not have conjunctions (And / Or)
3. It does not have side effects
Classes
• Definition of class: “family of functions with a clear
and well defined objective”
• This objective is the responsibility of the class
• Responsibility as a bunch of solutions to an actor
Actors / Roles
• Final user
• External systems
• Accountants / Stakeholders
• Software Architects
Classes and actors
A class must satisfy the needs of one actor,
and that actor only
If we do more than one thing
• Lines of code will grow without control
• Share code between different responsibilities
• Heterogeneous collaborators
• Classes are difficult to test
• Our code will be very hard to change
How to do one thing
1. Testing (TDD)
2. Extracting
4
4. “Abstractions in code,
details in data”
0 2 20 39
Id Name Address
Parsing a message
Benefits
• More robust design, as there are more immutable
parts
• We can code without knowing all the details (defer
details)
• Facilitates testing, as we can test the abstraction, not
specifics
• Details that are likely to change are not spread out in
the code, so it’s faster to find them
Get details out of your code!
• Data structures (OK, still code :))
• Properties files / YAML
• Environment variables
• Datastores
• Configuration server
One exception
Tests
5
Failing
test
Make it
pass
Refactor
TDD
Failing
test
Make it
better
Make it
work
Make it
pretty
5. “Make it work, make it
better, make it pretty”
My five mantras
1. Don’t leave broken windows
2. Extract till you drop
3. Do one thing, do it well, and do it only
4. Abstractions in code, details in data
5. Make it work, make it better, make it pretty
Questions?
Other mantras?
@_Raul_Avila
raul@raulavila.com

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My five mantras to write better Software