Solid code isn't flexible

Transcript

1. Chris Keathley / @ChrisKeathley / [email protected]
   SOLID code isn’t
   Flexible
   

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2. So, I’ve been taking a break
   

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5. Y
   o
   This Talk
   

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6. This talk isn’t really
   about SOLID
   

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7. This talk is
   
   
   about building systems
   
   
   with less
   
   
   stuff
   

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8. Single Responsibility
   
   
   Open/Closed Principle
   
   
   Liskov Substitution Principle
   
   
   Interface Segregation Principle
   
   
   Dependency Inversion Principle
   

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9. Single Responsibility
   
   
   Open/Closed Principle
   
   
   Liskov Substitution Principle
   
   
   Interface Segregation Principle
   
   
   Dependency Inversion Principle
   What is this in s
   er
   vice of?
   

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10. No one ever got fired for
    adopting an acronym
    

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11. Software Design is *really hard*.
    

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12. How do we make it easy to
    change software?
    

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13. How do we make it easy to
    change software?
    How do we add new
    functionality without changing
    any existing code?
    

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14. Lets Talk About:
    Fundamental Ideals
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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15. Lets Talk About:
    Fundamental Ideas
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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16. Premise 1
    Software Design is about
    managing complexity
    

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17. HTTP Client
    

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18. HTTP Client
    Socket Management
    

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19. HTTP Client
    Socket Management
    SSL
    

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20. HTTP Client
    Socket Management
    SSL
    Connection Pooling
    

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21. HTTP Client
    Socket Management
    SSL
    Connection Pooling
    h1.1 vs h2
    

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22. HTTP Client
    Socket Management
    SSL
    Connection Pooling
    h1.1 vs h2
    Parsing http payloads
    

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23. HTTP Client
    Socket Management
    SSL
    Connection Pooling
    h1.1 vs h2
    Parsing http payloads
    Essential
    
    
    C
    om
    pl
    ex
    ity
    

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24. Total Complexity
    Sum(essential complexity * interaction points)
    

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25. Total Complexity
    Sum(essential complexity * interaction points)
    Most often in the f
    or
    m of
    dependent code
    

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26. Dependencies
    Change h
    er
    e…
    Module A Module B
    Means Change h
    er
    e
    

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27. Premise 2
    All code has a cost.
    
    
    Anything we add to the system
    should add significant value.
    

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28. Lets Talk About:
    Fundamental Ideas
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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29. Lets Talk About:
    Fundamental Ideas
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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30. Lets Talk About:
    Fundamental Ideas
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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31. Total Complexity
    Sum(essential complexity * interaction points)
    

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32. Total Complexity
    Sum(essential complexity * 0)
    

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33. Encapsulation
    Not just f
    or
    y
    ou
    r state!
    

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34. Encapsulati
    o
    API
    

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35. Encapsulati
    o
    Shall
    ow
    lay
    e
    API
    

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36. Encapsulati
    o
    Deep
    er
    Lay
    e
    API
    

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37. Encapsulati
    o
    Best Case
    API
    

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38. HTTP Client
    

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39. HTTP Client
    TCP
    Y
    ou
    sh
    ou
    ld
    on
    ly have to see this stuff
    Not this…
    

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40. HTTP Client
    TCP
    MyOtherServiceClient
    Fuse Regulator
    

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41. HTTP Client
    TCP
    MyOtherServiceClient
    Fuse Regulator
    Gen
    er
    al
    Specific
    

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42. HTTP Client
    TCP
    MyOtherServiceClient
    Fuse Regulator
    Gen
    er
    al
    Specific
    M
    or
    e Reusable
    Less Reusable
    

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43. Examples
    MapSet
    Jason
    Network Protocols
    Persistent Term
    

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44. Red Flags
    Excessive passthrough or defdelegates
    Layered modules that share similar apis or functions
    Changes impacting multiple dependencies
    Pushing specific details into lower levels decreases
    reuse
    

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45. Lets Talk About:
    Fundamental Ideas
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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46. Lets Talk About:
    Fundamental Ideas
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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47. Handler
    Web Request
    Ecto
    Cache
    

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48. Handler
    Web Request
    Ecto
    Cache
    Wh
    er
    e do these go?
    

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49. How much of this is
    reusable?
    

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50. Who knows how to
    make these decisions?
    

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51. Handler
    Web Request
    Ecto
    Cache
    

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52. Handler
    Web Request
    Ecto
    Cache
    Is this still reusable?
    

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53. Handler
    Ecto
    Cache
    Can I use this
    functi
    on
    ?
    Background
    Task
    

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54. Handler
    Ecto
    Cache
    Are we g
    oi
    ng to
    need to tune this?
    Background
    Task
    

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55. Push specific logic upwards.
    
    
    Pull complexity downwards.
    

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56. Handler
    Ecto
    Cache
    Background
    Task
    

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57. Handler
    Ecto
    Cache
    Background
    Task
    

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58. Delete passthrough
    modules
    

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59. Handler Ecto
    Wrapper
    defmodule EctoWrapper do
    def one(query), do: Repo.one(query)
    def all(query), do: Repo.all(query)
    end
    

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60. Handler Ecto
    

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61. Remove modules
    that provide little
    value
    

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62. def get_posts(id) do
    
    
    case :fuse.check(:service) do
    
    
    :ok ->
    
    
    case call_service(id) do
    
    
    {:ok, result} ->
    
    
    :ok = Cache.put(id, result)
    
    
    {:ok, result}
    
    
    {:error, error} ->
    
    
    :fuse.melt(:service)
    
    
    {:error, error}
    
    
    end
    
    
    :blown ->
    
    
    cached = Cache.get(id)
    
    
    if cached do
    
    
    {:ok, result}
    
    
    else
    
    
    {:error, error}
    
    
    end
    
    
    end
    
    
    end
    

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63. def get_posts(id) do
    
    
    case :fuse.check(:service) do
    
    
    :ok ->
    
    
    case call_service(id) do
    
    
    {:ok, result} ->
    
    
    :ok = Cache.put(id, result)
    
    
    {:ok, result}
    
    
    {:error, error} ->
    
    
    :fuse.melt(:service)
    
    
    {:error, error}
    
    
    end
    
    
    :blown ->
    
    
    cached = Cache.get(id)
    
    
    if cached do
    
    
    {:ok, result}
    
    
    else
    
    
    {:error, error}
    
    
    end
    
    
    end
    
    
    end
    H
    ow
    does this
    s
    er
    vice int
    er
    act
    with the cache?
    

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64. def get_posts(id) do
    
    
    case :fuse.check(:service) do
    
    
    :ok ->
    
    
    case call_service(id) do
    
    
    {:ok, result} ->
    
    
    :ok = Cache.put(id, result)
    
    
    {:ok, result}
    
    
    {:error, error} ->
    
    
    :fuse.melt(:service)
    
    
    {:error, error}
    
    
    end
    
    
    :blown ->
    
    
    cached = Cache.get(id)
    
    
    if cached do
    
    
    {:ok, result}
    
    
    else
    
    
    {:error, error}
    
    
    end
    
    
    end
    
    
    end
    Finding a bug
    means reading
    the functi
    o
    

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65. def get_posts(id) do
    
    
    case :fuse.check(:service) do
    
    
    :ok ->
    
    
    case call_service(id) do
    
    
    {:ok, result} ->
    
    
    :ok = Cache.put(id, result)
    
    
    {:ok, result}
    
    
    {:error, error} ->
    
    
    :fuse.melt(:service)
    
    
    {:error, error}
    
    
    end
    
    
    :blown ->
    
    
    cached = Cache.get(id)
    
    
    if cached do
    
    
    {:ok, result}
    
    
    else
    
    
    {:error, error}
    
    
    end
    
    
    end
    
    
    end
    This is a
    “C
    om
    plete”
    
    
    Functi
    o
    

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66. Every function
    should do one thing
    and do it completely
    

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67. Each function
    should add value
    and provide reuse.
    

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68. A function’s
    signature should be
    much simpler than
    its implementation.
    

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69. Lets Talk About:
    Fundamental Ideas
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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70. Lets Talk About:
    Fundamental Ideas
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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71. Polymorphism
    Inversion of Control
    &
    

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72. Enum
    

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73. Enum
    S
    er
    i
    ou
    sly the
    best module ev
    e
    

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74. Enum
    Enum
    er
    able
    things go in
    Functi
    on
    s that
    op
    er
    ate
    on
    items
    

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75. Polymorphism in Elixir
    Functions Protocols Behaviours
    

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76. defmodule Animal do
    
    
    def speak(f) do
    
    
    f.()
    
    
    end
    
    
    end
    
    
    dog = fn -> "bark" end
    
    
    cat = fn -> "Worship me you lowly human" end
    
    
    Animal.speak(dog)
    
    
    Animal.speak(cat)
    

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77. Mentat.fetch(:posts_cache, :key, fn key ->
    
    
    case Service.get_posts(key) do
    
    
    {:ok, resp} ->
    
    
    {:commit, resp}
    
    
    {:error, e} ->
    
    
    {:ignore, e}
    
    
    end
    
    
    end)
    

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78. Polymorphism in Elixir
    Functions Protocols Behaviours
    

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79. Controller
    Web Request
    Other Service
    

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80. Controller
    Web Request
    Other Service
    Can we mock this
    ou
    t?
    

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81. defprotocol MyService do
    
    
    def get_posts(impl)
    
    
    end
    

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82. defprotocol MyService do
    
    
    def get_posts(impl)
    
    
    end
    
    
    defmodule MyService.HTTP do
    
    
    defstruct :url, :fuse
    
    
    defimpl MyService do
    
    
    def get_posts(%{url: url, fuse: fuse}) do
    
    
    case :fuse.check(fuse) do
    
    
    :ok ->
    
    
    Req.get(url)
    
    
    :blown ->
    
    
    {:error, Error.unavailable("Service is down")}
    
    
    end
    
    
    end
    
    
    end
    
    
    end
    

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83. defprotocol MyService do
    
    
    def get_posts(impl)
    
    
    end
    
    
    defmodule MyService.Mock do
    
    
    defstruct fake_response: %{}
    
    
    defimpl MyService do
    
    
    def get_posts(%{fake_response: fake_response}) do
    
    
    fake_response
    
    
    end
    
    
    end
    
    
    end
    

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84. real = %MyService.HTTP{}
    
    
    fake = %MyService.Mock{}
    
    
    MyService.get_posts(real)
    

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85. Controller
    Web Request
    Other Service
    

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86. Controller
    Web Request
    Other Service
    Inject the s
    tr
    uct
    into the plug
    c
    on
    n
    

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87. defmodule MyApp.Posts do
    
    
    def index(conn, _params) do
    
    
    service = conn.private[:service]
    
    
    MyService.get_posts(service)
    
    
    end
    
    
    end
    

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88. Polymorphism in Elixir
    Functions Protocols Behaviours
    

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89. Machinery Behaviour
    

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90. Machinery Behaviour
    Behavi
    ou
    rs
    ar
    e g
    oo
    d when
    
    
    y
    ou
    c
    on
    tr ol
    the machin
    er
    y
    arou
    nd them
    

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91. Lets Talk About:
    Fundamental Ideas
    Deep Layers vs Shallow Layers
    Things are better together
    Allowing for extension
    

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92. Don’t forget
    to ask “why”.
    

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93. Chris Keathley / @ChrisKeathley / [email protected]
    Thanks!
    

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