On 17th November across the globe the Global Day of CodeRetreat was happening. In Melbourne 28 Developers rocked up to code and learn together. Here are Melbourne's slides, including the chosen constraints for the day. Thanks to my awesome co-hosts, co-facilitators and co-organisers Tomasz Janowski (REA), Luke McCarthy (ThoughtWorks), Ren Koh (SEEK), Terence Duong (SEEK), Seamus Kearney (SEEK), Birgitta Mabbett (SEEK) and Kelly Benson (ThoughtWorks) for a great team effort to making the day successful and heaps of fun!

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November 17, 2018
Celebrating passion and craft
Melbourne,
Australia

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2000 Developers
130 Cities
6 Continents
18 Time zones

3. The Global Day of Coderetreat is happening thanks
to hundreds of Hosts and Facilitators worldwide!

4. Global Day of Coderetreat encourages you to donate to
CoderDojo.
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5. CoderDojo is a global volunteer-led community of free
programming clubs for young people between 7 and 17.
CoderDojo gives young people all over the world better
access to the “Magic behind the technology” that surrounds
us and touches almost everything that we do in our lives.
About CoderDojo
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6. Within CoderDojo there is a focus on developing creativity, a
sense of community, peer learning skills, mentoring and self
led learning with an emphasis on openness and showing how
coding can be a force for positive change.
About CoderDojo
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7. Local Sponsor
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8. Local Sponsor
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9. Local Sponsor
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10. Morning
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● 08:30 Intro to the Day
● 09:00 Practice session #1
● 10:00 Practice session #2
● 11:00 Practice session #3
● 12:00 Lunch break until 1:30PM

11. Afternoon
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● 1:30 Practice session #4
● 2:30 Practice session #5
● 3:30 Practice session #6
● 4:30 Closing circle
● 5:00 End of the event
● > 5pm Drinks & Nibbles

12. Coderetreat
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● Full day activity focused on the fundamentals
of software development and design
● The goal for developers at work is to finish
something
● The goal for them during coderetreat is to
practice, not to finish

13. Coderetreat
Challenge yourself!
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● Get out of your comfort zone
● Program in languages you don’t know
● Detach yourself from your own creation
● Do what you always wanted but couldn’t
● Don’t focus on finishing

14. Structure
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● Problem:
○ Conway’s Game of Life
● Session length:
○ 45 minutes followed by a 10 minute
retrospective
● Delete your code after each session!

15. Structure
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● Pair Programming
● TDD
● Kent Beck’s 4 rules of simple design
○ code passes the tests
○ reveals intention
○ no duplication
○ fewest elements
● Don’t forget to have fun!

16. Pair Programming
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17. Test Driven Development
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● Add failing test
● Run all tests
● Write code
● Run tests
● Refactor
● Repeat

18. Conway’s Game of Life
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● A zero-player game, meaning that its evolution is
determined by its initial state
● The universe of the Game of Life is an infinite
two-dimensional grid of square cells
● Every cell is in one of two possible states: alive or dead
● Every cell interacts with its eight neighbours, which are
the cells that are horizontally, vertically, or diagonally
adjacent

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Conway’s Game of Life

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Conway’s Game of Life
1. A living cell with fewer than two living
neighbors dies.

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Conway’s Game of Life
2. A living cell with more than three living
neighbors dies.

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Conway’s Game of Life
3. A dead cell with exactly three living
neighbors comes to life.

23. Session #1
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No constraints

24. No constraints
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● Get familiar with Conway’s
Game of Life
● Use your preferred language
● Remember to delete your
code after the session

25. Retrospective
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● What went well?
● What didn’t?
● What could be improved?

26. Session #2
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Ping Pong TDD

27. Ping Pong TDD
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● Work in pairs
● Person A only writes tests
● Person B only tries to get the
tests to pass
● Both persons refactor when
appropriate
● Person B swaps roles with A

28. Retrospective
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● What went well?
● What didn’t?
● What could be improved?

29. Session #3
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No Naked Primitives

30. No naked primitives
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Primitive Obsession (Code
Smell)
It is using primitive data types to
represent domain ideas.
Eg: String for a message, Integer
to hold currency etc.

31. No naked primitives
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Objective of the session -
● To practice avoiding primitive
obsession code smell.
● Creating required “Value Objects”
● Understanding encapsulation.

32. No naked primitives
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Adding an alive cell in position [3,4]
● Primitive obsession
const population = [ [], [], [], [], [], [] ];
population[3][4] = true;

33. No naked primitives
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Adding an alive cell in position [3,4]
● No primitives
const population = new Population();
const cell = new AliveCell();
const position = new Position(3, 4);
population.set(position, cell);

34. Retrospective
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● What went well?
● What didn’t?
● What could be improved?

35. Session #4
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Baby steps

36. Baby steps
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1. TDD
2. GIT (or similar)

37. Baby steps
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1. Set the timer (4 minutes)
2. Write exactly one test
3. Write implementation to make the
test pass
4. If within time - commit
Otherwise - revert
5. Repeat

38. Retrospective
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● What went well?
● What didn’t?
● What could be improved?

39. Session #5
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Pure functions

40. Pure functions
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● A function where the return
value is only determined by
its input values, without
observable side effects

41. Pure functions
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● A pure function can only access what you pass
it, so it’s easy to see its dependencies
● When a function accesses some other program
state, such as a global variable, it is no longer
pure.
● A given invocation of a pure function can be
replaced by its result. There’s no difference
between “add(2,3)” and “5”. This property is
called referential transparency

42. Pure functions
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● Easy to test
○ To test a pure function, you declare the values
that will act as arguments and pass them to the
function. The output value needs to be verified
against the expected value.
○ No context to set up, no current user or request
○ No side effects to mock or stub
○ Testing doesn’t get more straightforward than
this

43. Pure functions
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function add(a, b) {
return a + b;
}

44. Pure functions
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function add(a, b) {
formatHdd();
return a + b;
}

45. Pure functions
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function doubleArray(arr) {
return arr.map((a) => a * 2);
}

46. Pure functions
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function doubleArray(arr) {
for(let i = 0; i < arr.length; i++) {
arr[i] = arr[i] * 2;
}
return arr;
}

47. Pure functions
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function rollDice() {
return Math.floor(Math.random() * 6) + 1;
}

48. Pure functions
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function tomorrow() {
const now = new Date();
return new Date(now.getTime() +
(24 * 60 * 60 * 1000));
}

49. Pure functions
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function tomorrow(now) {
return new Date(now.getTime() +
(24 * 60 * 60 * 1000));
}

50. Retrospective
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● What went well?
● What didn’t?
● What could be improved?

51. Session #6
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Mute Ping Pong

52. Mute Ping Pong
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● Work in pairs
● Person A only writes tests
● Person B only tries to get the tests to
pass
● Both persons refactor when
appropriate
● Person B swaps roles with A
● A and B can’t talk to each other

53. Retrospective
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● What went well?
● What didn’t?
● What could be improved?

54. Bonus “Session”
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Let’s tell Germany to
stop, delete their
code & stand up!

55. Bonus “Language”
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G’Day Deutschland!
Shtop! Loesh Dinen
Code. Oond shtey auf.
(#GDCR18, Melbourne, Australia, 17th Nov ‘18)

56. Closing Circle
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● What, if anything, did you
learn today?
● What, if anything, surprised
you today?
● What, if anything, will you do
differently in the future?

57. Thanks for coming!
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Thanks for attending
GDCR 2018
Stick around for some drinks,
nibbles and networking!