Refactoring Elixir - Lessons Learned from a Year on exercism.io

There's a lot you can learn about the pitfalls of a language when you see literally hundreds of people all solving the same problems - and frequently making the same mistakes! In this talk we're going to start with some common, but less than optimal, solutions to some of the problems on exercism.io, and we'll do a step by step refactoring. We'll also add in some benchmarking to the existing exercism.io test suites to show the performance benefits of some of the refactoring that we do, and discuss the tradeoffs of the decisions that we're making to illustrate why this refactoring is beneficial.
Devon is a Software Engineer at EducationSuperHighway. When he's not writing Ruby at work, he can be found contributing to open source projects in Elixir. Away from the computer he's a husband, father and chess player.

1. Devon Estes ElixirConf EU 2017 @devoncestes REFACTORING ELIXIR LESSONS LEARNED FROM A YEAR ON EXERCISM.IO
2. REFACTORING IS A CONTROLLED TECHNIQUE FOR IMPROVING THE DESIGN OF AN EXISTING CODE BASE. ITS ESSENCE IS APPLYING A SERIES OF SMALL BEHAVIOR- PRESERVING TRANSFORMATIONS, EACH OF WHICH IS "TOO SMALL TO BE WORTH DOING”. Martin Fowler Devon Estes ElixirConf EU 2017 @devoncestes
3. Devon Estes ElixirConf EU 2017 @devoncestes WHY REFACTOR?
4. Devon Estes ElixirConf EU 2017 @devoncestes •Easier to read/understand WHY REFACTOR?
5. Devon Estes ElixirConf EU 2017 @devoncestes •Easier to read/understand •Easier to change WHY REFACTOR?
6. Devon Estes ElixirConf EU 2017 @devoncestes •Easier to read/understand •Easier to change •Lower complexity WHY REFACTOR?
7. Devon Estes ElixirConf EU 2017 @devoncestes •Easier to read/understand •Easier to change •Lower complexity •Increase performance WHY REFACTOR?
8. Devon Estes ElixirConf EU 2017 @devoncestes •Easier to read/understand •Easier to change •Lower complexity •Increase performance* *Some people think this isn’t really part of refactoring. I do. WHY REFACTOR?
9. Devon Estes ElixirConf EU 2017 @devoncestes •Easier to read/understand •Easier to change •Lower complexity •Increase performance* *Some people think this isn’t really part of refactoring. I do. WHY REFACTOR?
10. Devon Estes ElixirConf EU 2017 @devoncestes •Easier to read/understand •Lower complexity •Increase performance* *Some people think this isn’t really part of refactoring. I do. WHY REFACTOR?
11. Devon Estes ElixirConf EU 2017 @devoncestes MAKE CODE “BETTER”
12. Devon Estes ElixirConf EU 2017 @devoncestes
13. Devon Estes ElixirConf EU 2017 @devoncestes EXERCISM IS A PLACE WHERE PEOPLE CAN IMPROVE THEIR PROGRAMMING SKILLS BY SOLVING TOY PROBLEMS AND THEN HAVING FRIENDLY AND RICH DISCUSSIONS ABOUT THE WAYS TO MAKE THE CODE BETTER. Katrina Owen
14. EXERCISM IS GREAT FOR THIS! Devon Estes ElixirConf EU 2017 @devoncestes
15. Devon Estes ElixirConf EU 2017 @devoncestes BINARY SEARCH
16. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.Cond do def search(items, value) do end end
17. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.Cond do def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end defp search(items, value, bottom, top) do end end
18. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.Cond do def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) end end
19. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.Cond do def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) cond do end end end
20. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.Cond do def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) cond do bottom > top -> :not_found end end end
21. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.Cond do def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) cond do bottom > top -> :not_found middle_elem == value -> {:ok, middle_idx} end end end
22. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.Cond do def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) cond do bottom > top -> :not_found middle_elem == value -> {:ok, middle_idx} middle_elem < value -> search(items, value, middle_idx + 1, top) end end end
23. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.Cond do def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) cond do bottom > top -> :not_found middle_elem == value -> {:ok, middle_idx} middle_elem < value -> search(items, value, middle_idx + 1, top) true -> search(items, value, bottom, middle_idx - 1) end end end
24. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.Cond do def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) cond do bottom > top -> :not_found middle_elem == value -> {:ok, middle_idx} middle_elem < value -> search(items, value, middle_idx + 1, top) true -> search(items, value, bottom, middle_idx - 1) end end end
25. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.PatternMatching do def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) end
26. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.PatternMatching do def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) search(items, value, bottom, top, middle_idx, middle_elem) end end
27. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.PatternMatching do def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) search(items, value, bottom, top, middle_idx, middle_elem) end defp search(_, value, _, _, middle_idx, middle_elem) when value == middle_elem, do: {:ok, middle_idx} end
28. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.PatternMatching do def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) search(items, value, bottom, top, middle_idx, middle_elem) end defp search(_, value, _, _, middle_idx, middle_elem) when value == middle_elem, do: {:ok, middle_idx} defp search(_, _, bottom, top, _, _) when bottom > top, do: :not_found end
29. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.PatternMatching do def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) search(items, value, bottom, top, middle_idx, middle_elem) end defp search(_, value, _, _, middle_idx, middle_elem) when value == middle_elem, do: {:ok, middle_idx} defp search(_, _, bottom, top, _, _) when bottom > top, do: :not_found defp search(items, value, _, top, middle_idx, middle_elem) when middle_elem < value, do: search(items, value, middle_idx + 1, top) end
30. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.PatternMatching do def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) defp search(items, value, bottom, top) do middle_idx = div(bottom + top, 2) middle_elem = elem(items, middle_idx) search(items, value, bottom, top, middle_idx, middle_elem) end defp search(_, value, _, _, middle_idx, middle_elem) when value == middle_elem, do: {:ok, middle_idx} defp search(_, _, bottom, top, _, _) when bottom > top, do: :not_found defp search(items, value, _, top, middle_idx, middle_elem) when middle_elem < value, do: search(items, value, middle_idx + 1, top) defp search(items, value, bottom, _, middle_idx, middle_elem) do: search(items, value, bottom, middle_idx - 1) end
31. Devon Estes ElixirConf EU 2017 @devoncestes defmodule BinarySearch.PatternMatching do def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) defp search(items, value, bottom, top), do: search(items, value, bottom, top, div(bottom + top, 2)) defp search(items, value, bottom, top, middle_idx), do: search(items, value, bottom, top, middle_idx, elem(items, middle_idx)) defp search(_, value, _, _, middle_idx, middle_elem) when value == middle_elem, do: {:ok, middle_idx} defp search(_, _, bottom, top, _, _) when bottom > top, do: :not_found defp search(items, value, _, top, middle_idx, middle_elem) when middle_elem < value, do: search(items, value, middle_idx + 1, top) defp search(items, value, bottom, _, middle_idx, middle_elem) do: search(items, value, bottom, middle_idx - 1) end
32. Devon Estes ElixirConf EU 2017 @devoncestes bench_func = fn(module) -> end
33. Devon Estes ElixirConf EU 2017 @devoncestes bench_func = fn(module) -> module.search({1, 2, 3, 4, 5}, 1) module.search({1, 2, 3, 4, 5}, 3) module.search({1, 2, 3, 4, 5}, 5) module.search({1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377}, 3) module.search({1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377}, 34) module.search({1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377}, 377) end
34. Devon Estes ElixirConf EU 2017 @devoncestes bench_func = fn(module) -> module.search({1, 2, 3, 4, 5}, 1) module.search({1, 2, 3, 4, 5}, 3) module.search({1, 2, 3, 4, 5}, 5) module.search({1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377}, 3) module.search({1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377}, 34) module.search({1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377}, 377) end Benchee.run(%{ "pattern matching" => fn -> bench_func.(BinarySearch.PatternMatching) end, "cond statement" => fn -> bench_func.(BinarySearch.Cond) end, }, time: 10)
35. Devon Estes ElixirConf EU 2017 @devoncestes Name ips average deviation median cond statement 763.25 K 1.31 μs ±379.72% 1.20 μs pattern matching 717.96 K 1.39 μs ±362.90% 1.20 μs Comparison: cond statement 763.25 K pattern matching 717.96 K - 1.06x slower
36. Devon Estes ElixirConf EU 2017 @devoncestes BINARY SEARCH Pattern Matching Cond Statement Readability Complexity Performance
37. Devon Estes ElixirConf EU 2017 @devoncestes BINARY SEARCH Pattern Matching Cond Statement Readability Complexity Performance
38. Devon Estes ElixirConf EU 2017 @devoncestes BINARY SEARCH Pattern Matching Cond Statement Readability Complexity Performance
39. Devon Estes ElixirConf EU 2017 @devoncestes BINARY SEARCH Pattern Matching Cond Statement Readability Complexity Performance
40. Devon Estes ElixirConf EU 2017 @devoncestes SPACE AGE
41. Devon Estes ElixirConf EU 2017 @devoncestes defmodule SpaceAge.MapLookup do def age_on(planet, seconds) do lookup = %{ earth: 1.0, mercury: 0.2408467, venus: 0.61519726, mars: 1.8808158, jupiter: 11.862615, saturn: 29.447498, uranus: 84.016846, neptune: 164.79132 } end end
42. Devon Estes ElixirConf EU 2017 @devoncestes defmodule SpaceAge.MapLookup do def age_on(planet, seconds) do lookup = %{ earth: 1.0, mercury: 0.2408467, venus: 0.61519726, mars: 1.8808158, jupiter: 11.862615, saturn: 29.447498, uranus: 84.016846, neptune: 164.79132 } seconds / (lookup[planet] * 31557600) end end
43. Devon Estes ElixirConf EU 2017 @devoncestes defmodule SpaceAge.MapLookup do @earth_year 31557600 def age_on(planet, seconds) do lookup = %{ earth: 1.0, mercury: 0.2408467, venus: 0.61519726, mars: 1.8808158, jupiter: 11.862615, saturn: 29.447498, uranus: 84.016846, neptune: 164.79132 } seconds / (lookup[planet] * @earth_year) end end
44. Devon Estes ElixirConf EU 2017 @devoncestes defmodule SpaceAge.MapLookup do @earth_year 31557600 @planet_year_lengths %{ earth: 1.0, mercury: 0.2408467, venus: 0.61519726, mars: 1.8808158, jupiter: 11.862615, saturn: 29.447498, uranus: 84.016846, neptune: 164.79132 } def age_on(planet, seconds), do: seconds / (@planet_year_lengths[planet] * @earth_year) end
45. Devon Estes ElixirConf EU 2017 @devoncestes defmodule SpaceAge.PatternMatching do @earth_year 31557600 def age_on(planet, seconds), do: seconds / (planet_rel_years(planet) * @earth_year) defp planet_rel_years(:mercury), do: 0.2408467 defp planet_rel_years(:venus), do: 0.61519726 defp planet_rel_years(:earth), do: 1.0 defp planet_rel_years(:mars), do: 1.8808158 defp planet_rel_years(:jupiter), do: 11.862615 defp planet_rel_years(:saturn), do: 29.447498 defp planet_rel_years(:uranus), do: 84.016846 defp planet_rel_years(:neptune), do: 164.79132 end
46. Devon Estes ElixirConf EU 2017 @devoncestes Name ips average deviation median pattern matching 1.54 M 0.65 μs ±1081.97% 0.60 μs map lookup 0.82 M 1.22 μs ±440.35% 1.10 μs Comparison: pattern matching 1.54 M map lookup 0.82 M - 1.88x slower
47. Devon Estes ElixirConf EU 2017 @devoncestes defmodule SpaceAge.Macros do @earth_year 31557600 def age_on(planet, seconds), do: seconds / planet_rel_years(planet) defp planet_rel_years(:mercury), do: unquote(0.2408467 * @earth_year) defp planet_rel_years(:venus), do: unquote(0.61519726 * @earth_year) defp planet_rel_years(:earth), do: unquote(@earth_year) defp planet_rel_years(:mars), do: unquote(1.8808158 * @earth_year) defp planet_rel_years(:jupiter), do: unquote(11.862615 * @earth_year) defp planet_rel_years(:saturn), do: unquote(29.447498 * @earth_year) defp planet_rel_years(:uranus), do: unquote(84.016846 * @earth_year) defp planet_rel_years(:neptune), do: unquote(164.79132 * @earth_year) end
48. Devon Estes ElixirConf EU 2017 @devoncestes Name ips average deviation median macros 1.85 M 0.54 μs ±1178.22% 0.50 μs pattern matching 1.58 M 0.63 μs ±1133.03% 0.60 μs map lookup 0.88 M 1.14 μs ±471.56% 1.00 μs Comparison: macros 1.85 M pattern matching 1.58 M - 1.17x slower map lookup 0.88 M - 2.10x slower
49. Devon Estes ElixirConf EU 2017 @devoncestes SPACE AGE Pattern Matching Map Lookup Macros Readability Lower Complexity Performance
50. Devon Estes ElixirConf EU 2017 @devoncestes SPACE AGE Pattern Matching Map Lookup Macros Readability Lower Complexity Performance
51. Devon Estes ElixirConf EU 2017 @devoncestes SPACE AGE Pattern Matching Map Lookup Macros Readability Lower Complexity Performance
52. Devon Estes ElixirConf EU 2017 @devoncestes SPACE AGE Map Lookup Pattern Matching Macros Readability Lower Complexity Performance
53. Devon Estes ElixirConf EU 2017 @devoncestes
54. Devon Estes ElixirConf EU 2017 @devoncestes ALLERGIES
55. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.Hash do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } end
56. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.Hash do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } def allergic_to?(flags, item), do: item in list(flags) end
57. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.Hash do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } def allergic_to?(flags, item), do: item in list(flags) def list(flags) do end end
58. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.Hash do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } def allergic_to?(flags, item), do: item in list(flags) def list(flags) do flags |> Integer.digits(2) end end
59. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.Hash do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } def allergic_to?(flags, item), do: item in list(flags) def list(flags) do flags |> Integer.digits(2) |> Enum.reverse() end end
60. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.Hash do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } def allergic_to?(flags, item), do: item in list(flags) def list(flags) do flags |> Integer.digits(2) |> Enum.reverse() |> Enum.zip(@allergies) end end
61. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.Hash do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } def allergic_to?(flags, item), do: item in list(flags) def list(flags) do flags |> Integer.digits(2) |> Enum.reverse() |> Enum.zip(@allergies) |> Enum.reduce([], fn {1, {_, allergy}}, acc -> [allergy | acc] _, acc -> acc end) end end
62. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.BitShifting do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } end
63. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.BitShifting do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } def allergic_to?(flags, item), do: item in list(flags) end
64. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.BitShifting do @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } def allergic_to?(flags, item), do: item in list(flags) def list(flags) do Enum.filter_map(@allergies, &(flagged? flags, &1), fn({_, item}) -> item end) end end
65. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.BitShifting do use Bitwise, only_operators: true @allergies %{ 1 => "eggs", 2 => "peanuts", 4 => "shellfish", 8 => "strawberries", 16 => "tomatoes", 32 => "chocolate", 64 => "pollen", 128 => "cats", } def allergic_to?(flags, item), do: item in list(flags) def list(flags) do Enum.filter_map(@allergies, &(flagged? flags, &1), fn({_, item}) -> item end) end defp flagged?(flags, {value, _}) do (flags &&& value) > 0 end end
66. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.PatternMatching do def allergic_to?(flags, item), do: item in list(flags) end
67. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.PatternMatching do def allergic_to?(flags, item), do: item in list(flags) def list(flags), do: list(<<flags>>, []) end
68. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.PatternMatching do def allergic_to?(flags, item), do: item in list(flags) def list(flags), do: list(<<flags>>, []) defp list(<<1 :: size(1), r :: size(7)>>, acc), do: list(<<0 :: size(1), r :: size(7)>>, ["cats"|acc]) end
69. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.PatternMatching do def allergic_to?(flags, item), do: item in list(flags) def list(flags), do: list(<<flags>>, []) defp list(<<1 :: size(1), r :: size(7)>>, acc), do: list(<<0 :: size(1), r :: size(7)>>, ["cats"|acc]) defp list(<<l :: size(1), 1 :: size(1), r :: size(6)>>, acc), do: list(<<l :: size(1), 0 :: size(1), r :: size(6)>>, ["pollen"|acc]) end
70. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.PatternMatching do def allergic_to?(flags, item), do: item in list(flags) def list(flags), do: list(<<flags>>, []) defp list(<<1 :: size(1), r :: size(7)>>, acc), do: list(<<0 :: size(1), r :: size(7)>>, ["cats"|acc]) defp list(<<l :: size(1), 1 :: size(1), r :: size(6)>>, acc), do: list(<<l :: size(1), 0 :: size(1), r :: size(6)>>, ["pollen"|acc]) defp list(<<l :: size(2), 1 :: size(1), r :: size(5)>>, acc), do: list(<<l :: size(2), 0 :: size(1), r :: size(5)>>, ["chocolate"|acc]) end
71. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.PatternMatching do def allergic_to?(flags, item), do: item in list(flags) def list(flags), do: list(<<flags>>, []) defp list(<<1 :: size(1), r :: size(7)>>, acc), do: list(<<0 :: size(1), r :: size(7)>>, ["cats"|acc]) defp list(<<l :: size(1), 1 :: size(1), r :: size(6)>>, acc), do: list(<<l :: size(1), 0 :: size(1), r :: size(6)>>, ["pollen"|acc]) defp list(<<l :: size(2), 1 :: size(1), r :: size(5)>>, acc), do: list(<<l :: size(2), 0 :: size(1), r :: size(5)>>, ["chocolate"|acc]) defp list(<<l :: size(3), 1 :: size(1), r :: size(4)>>, acc), do: list(<<l :: size(3), 0 :: size(1), r :: size(4)>>, ["tomatoes"|acc]) defp list(<<l :: size(4), 1 :: size(1), r :: size(3)>>, acc), do: list(<<l :: size(4), 0 :: size(1), r :: size(3)>>, ["strawberries"|acc]) defp list(<<l :: size(5), 1 :: size(1), r :: size(2)>>, acc), do: list(<<l :: size(5), 0 :: size(1), r :: size(2)>>, ["shellfish"|acc]) defp list(<<l :: size(6), 1 :: size(1), r :: size(1)>>, acc), do: list(<<l :: size(6), 0 :: size(1), r :: size(1)>>, ["peanuts"|acc]) defp list(<<l :: size(7), 1 :: size(1)>>, acc), do: list(<<l :: size(7), 0 :: size(1)>>, ["eggs"|acc]) end
72. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.PatternMatching do def allergic_to?(flags, item), do: item in list(flags) def list(flags), do: list(<<flags>>, []) defp list(<<1 :: size(1), r :: size(7)>>, acc), do: list(<<0 :: size(1), r :: size(7)>>, ["cats"|acc]) defp list(<<l :: size(1), 1 :: size(1), r :: size(6)>>, acc), do: list(<<l :: size(1), 0 :: size(1), r :: size(6)>>, ["pollen"|acc]) defp list(<<l :: size(2), 1 :: size(1), r :: size(5)>>, acc), do: list(<<l :: size(2), 0 :: size(1), r :: size(5)>>, ["chocolate"|acc]) defp list(<<l :: size(3), 1 :: size(1), r :: size(4)>>, acc), do: list(<<l :: size(3), 0 :: size(1), r :: size(4)>>, ["tomatoes"|acc]) defp list(<<l :: size(4), 1 :: size(1), r :: size(3)>>, acc), do: list(<<l :: size(4), 0 :: size(1), r :: size(3)>>, ["strawberries"|acc]) defp list(<<l :: size(5), 1 :: size(1), r :: size(2)>>, acc), do: list(<<l :: size(5), 0 :: size(1), r :: size(2)>>, ["shellfish"|acc]) defp list(<<l :: size(6), 1 :: size(1), r :: size(1)>>, acc), do: list(<<l :: size(6), 0 :: size(1), r :: size(1)>>, ["peanuts"|acc]) defp list(<<l :: size(7), 1 :: size(1)>>, acc), do: list(<<l :: size(7), 0 :: size(1)>>, ["eggs"|acc]) defp list(_, acc), do: acc end
73. Devon Estes ElixirConf EU 2017 @devoncestes
74. Devon Estes ElixirConf EU 2017 @devoncestes defmodule Allergies.PatternMatching do def allergic_to?(flags, item), do: item in list(flags) def list(flags), do: list(<<flags>>, []) defp list(<<1 :: size(1), r :: size(7)>>, acc), do: list(<<0 :: size(1), r :: size(7)>>, ["cats"|acc]) defp list(<<l :: size(1), 1 :: size(1), r :: size(6)>>, acc), do: list(<<l :: size(1), 0 :: size(1), r :: size(6)>>, ["pollen"|acc]) defp list(<<l :: size(2), 1 :: size(1), r :: size(5)>>, acc), do: list(<<l :: size(2), 0 :: size(1), r :: size(5)>>, ["chocolate"|acc]) defp list(<<l :: size(3), 1 :: size(1), r :: size(4)>>, acc), do: list(<<l :: size(3), 0 :: size(1), r :: size(4)>>, ["tomatoes"|acc]) defp list(<<l :: size(4), 1 :: size(1), r :: size(3)>>, acc), do: list(<<l :: size(4), 0 :: size(1), r :: size(3)>>, ["strawberries"|acc]) defp list(<<l :: size(5), 1 :: size(1), r :: size(2)>>, acc), do: list(<<l :: size(5), 0 :: size(1), r :: size(2)>>, ["shellfish"|acc]) defp list(<<l :: size(6), 1 :: size(1), r :: size(1)>>, acc), do: list(<<l :: size(6), 0 :: size(1), r :: size(1)>>, ["peanuts"|acc]) defp list(<<l :: size(7), 1 :: size(1)>>, acc), do: list(<<l :: size(7), 0 :: size(1)>>, ["eggs"|acc]) defp list(_, acc), do: acc end
75. Devon Estes ElixirConf EU 2017 @devoncestes Name ips average deviation median pattern matching 3.70 K 270.07 μs ±28.97% 249.00 μs bit shifting 2.02 K 495.19 μs ±29.30% 461.00 μs map 0.62 K 1617.88 μs ±22.87% 1517.00 μs Comparison: pattern matching 3.70 K bit shifting 2.02 K - 1.83x slower map 0.62 K - 5.99x slower
76. Devon Estes ElixirConf EU 2017 @devoncestes ALLERGIES Map Lookup Bit Shifting Pattern Matching Readability Lower Complexity Performance
77. Devon Estes ElixirConf EU 2017 @devoncestes ALLERGIES Map Lookup Bit Shifting Pattern Matching Readability Lower Complexity Performance
78. Devon Estes ElixirConf EU 2017 @devoncestes ALLERGIES Map Lookup Bit Shifting Pattern Matching Readability Lower Complexity Performance
79. Devon Estes ElixirConf EU 2017 @devoncestes ALLERGIES Map Lookup Bit Shifting Pattern Matching Readability Lower Complexity Performance
80. Devon Estes ElixirConf EU 2017 @devoncestes WHAT’S THE POINT?
81. Devon Estes ElixirConf EU 2017 @devoncestes
82. Devon Estes ElixirConf EU 2017 @devoncestes ECONOMICS IS THE STUDY OF CHOICE IN A WORLD OF SCARCITY
83. Devon Estes ElixirConf EU 2017 @devoncestes
84. Devon Estes ElixirConf EU 2017 @devoncestes LET’S NUDGE!
85. Devon Estes ElixirConf EU 2017 @devoncestes •Lead by example LET’S NUDGE!
86. Devon Estes ElixirConf EU 2017 @devoncestes •Lead by example •Talk more about your mistakes LET’S NUDGE!
87. Devon Estes ElixirConf EU 2017 @devoncestes
88. Devon Estes ElixirConf EU 2017 @devoncestes •Lead by example •Talk more about your mistakes •More/better tooling LET’S NUDGE!
89. Devon Estes ElixirConf EU 2017 @devoncestes
90. Devon Estes ElixirConf EU 2017 @devoncestes def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end
91. Devon Estes ElixirConf EU 2017 @devoncestes def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end def search(items, value), do: search(items, value, 0, tuple_size(items) - 1)
92. Devon Estes ElixirConf EU 2017 @devoncestes def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) def search(items, value), do: search(items, value, 0, tuple_size(items) - 1)
93. Devon Estes ElixirConf EU 2017 @devoncestes def search(items, value) do search(items, value, 0, tuple_size(items) - 1) end def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) def search(items, value), do: search(items, value, 0, tuple_size(items) - 1) def search(items, value), do: search(items, value, 0, tuple_size(items) - 1)
94. Devon Estes ElixirConf EU 2017 @devoncestes flags |> Integer.digits(2) |> Enum.reverse() |> Enum.zip(@allergies)
95. Devon Estes ElixirConf EU 2017 @devoncestes flags |> Integer.digits(2) |> Enum.reverse() |> Enum.zip(@allergies) flags |> Integer.digits(2) |> Enum.reverse() |> Enum.zip(@allergies)
96. Devon Estes ElixirConf EU 2017 @devoncestes flags |> Integer.digits(2) |> Enum.reverse() |> Enum.zip(@allergies) flags |> Integer.digits(2) |> Enum.reverse() |> Enum.zip(@allergies) @allergens |> Enum.with_index() |> Enum.filter_map(&(flagged? flags, &1), fn({item, _}) -> item end)
97. Devon Estes ElixirConf EU 2017 @devoncestes “WE BEGAN THIS RESEARCH WITH THE NOTION THAT USING TYPOGRAPHIC CUES TO HIGHLIGHT IMPORTANT INFORMATION SOURCES IN PROGRAMS WOULD LEAD TO DRAMATIC IMPROVEMENTS IN COMPREHENSION. THE IMPROVEMENTS WE OBSERVED WERE MORE MODEST, DAMPENING OUR ENTHUSIASM. TYPOGRAPHIC SIGNALING HELPS, BUT NOT THAT MUCH. RESEARCH ON TEXT COMPREHENSION AGREES WITH THESE FINDINGS.” DOES SIGNALING HELP PROFESSIONAL PROGRAMMERS READ AND UNDERSTAND COMPUTER PROGRAMS - EDWARD M. GELLENBECK & CURTIS R. COOK
98. Devon Estes ElixirConf EU 2017 @devoncestes I HAVE NO IDEA WHAT I’M TALKING ABOUT, AND NO ONE SHOULD EVER TAKE ME SERIOUSLY, BUT…
99. Devon Estes ElixirConf EU 2017 @devoncestes DON’T MAKE ME THINK ABOUT FORMATTING
100. Devon Estes ElixirConf EU 2017 @devoncestes JUST TELL ME WHAT TO DO
101. Devon Estes ElixirConf EU 2017 @devoncestes BETTER YET, LET A TOOL DO IT FOR ME
102. Devon Estes ElixirConf EU 2017 @devoncestes elixirfmt
103. Devon Estes ElixirConf EU 2017 @devoncestes