Functional Object-Oriented Programming

One of the only certainties of software development is change. This change can often be painful because it means that we have to refactor or rewrite large quantities of our application. In order to ease the pain, programmers have developed a number of rules and techniques and codified them as "Best Practices". This is especially true in Object Oriented Programming.

Using real world examples we will discuss the strengths and weaknesses of OOP and explore the strengths and benefits of applying functional programming to our OOP code.

Transcript

1. FUNCTIONAL OBJECT-ORIENTED
   PROGRAMMING
   Chris Keathley / @ChrisKeathley / keathley@carbonfive.com
   

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2. What this talk
   isn’t about
   

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3. “OO IS EVIL!!!”
   - People on the internet
   

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4. “OO IS EVIL!!!”
   - People on the internet
   Kthnxbye
   

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5. OO vs FP
   

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6. I was trained in this
   

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7. C
   

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8. int main(int argc, char** argv)
   {
   mpc_parser_t* Number = mpc_new("number");
   mpc_parser_t* Symbol = mpc_new("symbol");
   mpc_parser_t* Sexpr = mpc_new("sexpr");
   mpc_parser_t* Qexpr = mpc_new("qexpr");
   mpc_parser_t* Expr = mpc_new("expr");
   mpc_parser_t* Lispy = mpc_new("lispy");
   mpca_lang(MPC_LANG_DEFAULT,
   " \
   number : /-?[0-9]+/ ; \
   symbol : '+' | '-' | '*' | '/' ; \
   sexpr : '(' * ')' ; \
   qexpr : '{' * '}' ; \
   expr : | | ; \
   lispy : /^/ * /$/ ; \
   ",
   Number, Symbol, Sexpr, Qexpr, Expr, Lispy);
   puts("Crisp Version 0.0.0.1");
   puts("Press Ctrl+c to Exit\n");
   while (1) {
   char* input = readline("crisp> ");
   add_history(input);
   mpc_result_t r;
   if (mpc_parse("", input, Lispy, &r)) {
   lval* x = lval_eval(lval_read(r.output));
   lval_println(x);
   lval_del(x);
   mpc_ast_delete(r.output);
   } else {
   mpc_err_print(r.error);
   mpc_err_delete(r.error);
   

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9. int main(int argc, char** argv)
   {
   mpc_parser_t* Number = mpc_new("number");
   mpc_parser_t* Symbol = mpc_new("symbol");
   mpc_parser_t* Sexpr = mpc_new("sexpr");
   mpc_parser_t* Qexpr = mpc_new("qexpr");
   mpc_parser_t* Expr = mpc_new("expr");
   mpc_parser_t* Lispy = mpc_new("lispy");
   mpca_lang(MPC_LANG_DEFAULT,
   " \
   number : /-?[0-9]+/ ; \
   symbol : '+' | '-' | '*' | '/' ; \
   sexpr : '(' * ')' ; \
   qexpr : '{' * '}' ; \
   expr : | | ; \
   lispy : /^/ * /$/ ; \
   ",
   Number, Symbol, Sexpr, Qexpr, Expr, Lispy);
   puts("Crisp Version 0.0.0.1");
   puts("Press Ctrl+c to Exit\n");
   while (1) {
   char* input = readline("crisp> ");
   add_history(input);
   mpc_result_t r;
   if (mpc_parse("", input, Lispy, &r)) {
   lval* x = lval_eval(lval_read(r.output));
   lval_println(x);
   lval_del(x);
   mpc_ast_delete(r.output);
   } else {
   mpc_err_print(r.error);
   mpc_err_delete(r.error);
   wtfbbq
   

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10. Java
    

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11. What is Object-Oriented
    Programming?
    

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12. OBJECT ORIENTED LANGUAGES HAVE…
    ▸ Behavior + Data (encapsulation)
    ▸ Classes
    ▸ Objects (instances of classes)
    ▸ Inheritance
    ▸ Methods
    ▸ Polymorphism
    

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13. OBJECT ORIENTED PROGRAMMING IMPLIES…
    ▸ State
    ▸ Mutability
    ▸ Encapsulation
    ▸ Domain modeling
    ▸ Message passing
    

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14. ANIMALS
    

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15. ANIMALS
    BIRDS
    

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16. ANIMALS
    BIRDS DOGS
    

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17. How do we use Oop?
    

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18. I read lots of books
    

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19. THE CLASSICS
    ▸ Design Patterns (Gang of 4)
    ▸ Growing Object-Oriented Software with Tests
    ▸ Practical Object-Oriented Design in Ruby
    ▸ Domain Driven Design
    ▸ Patterns of Enterprise Application Architecture
    

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20. I Learned best Practices
    

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21. BEST PRACTICES
    ▸ SOLID
    ▸ DRY
    ▸ Law of Demeter
    ▸ Small Methods
    ▸ Design by Contract
    ▸ TDD
    ▸ BDD
    ▸ Commands and Queries
    ▸ Tell don’t ask
    ▸ Separation of Concerns
    

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22. Un-enforced Best
    Practices will
    eventually be violated
    

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23. Complexity
    “CONSISTING OF MANY DIFFERENT
    AND CONNECTED PARTS”
    

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24. Simple
    “COMPOSED OF A SINGLE ELEMENT.”
    

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25. Decoupling
    

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26. Complexity is the death
    of productivity
    

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27. “the first 90% of all
    software products is the
    MVP, the other 90% is
    maintenance”
    - Greg O.
    

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28. OOP is
    complex
    By Nature
    

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29. Encapsulation
    STATE
    BEHAVIOR
    

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30. Inheritance
    ANIMALS
    BIRDS
    

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31. Inheritance
    ANIMALS
    BIRDS
    

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32. State
    FOO BAR BAZ
    

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33. State
    FOO BAR BAZ
    ME
    

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34. State
    FOO BAR BAZ
    ME
    Foo
    

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35. State
    FOO BAR BAZ
    ME
    Foo
    Bar
    

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36. State
    FOO BAR BAZ
    ME
    Foo Baz
    Bar
    

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37. Methods
    FOO
    STATE
    PRIVATE
    METHOD
    PRIVATE
    METHOD
    

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38. I combat complexity
    with Functional
    Programming
    

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39. functional
    Programming
    pure functions
    immutable data
    isolate side-effects
    Compose pipelines of functions
    

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40. functional
    Programming
    pure functions
    immutable data
    isolate side-effects
    Compose pipelines of functions
    

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41. Pure Functions
    (+2)
    3 5
    Always return the same result given
    the same arguments
    

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42. Pure Functions
    Have no side effects
    FS
    DB
    +
    

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43. Pure Functions
    # Pure
    def add(x, y)
    x + y
    end
    # Impure
    def user_input_add(x)
    print "Enter a number: "
    num = gets
    puts x + num.to_i
    end
    

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44. functional
    Programming
    pure functions
    immutable data
    isolate side-effects
    Compose pipelines of functions
    

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45. Immutability
    test "users can be fed" do
    user = User.new
    assert user.hungry? == true
    user.feed(Hamburger.new)
    assert user.hungry? == false
    end
    class User
    def initialize(stomach: [])
    @stomach = stomach
    end
    def feed(item)
    @stomach << item
    end
    end
    

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46. Immutability
    test "users can be fed" do
    user = User.new
    assert user.hungry? == true
    fed_user = user.feed(Hamburger.new)
    assert fed_user.hungry? == false
    end
    class User
    def initialize(stomach: [])
    @stomach = stomach
    end
    def feed(item)
    @stomach << item
    end
    end
    

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47. Immutability
    test "users can be fed" do
    user = User.new
    assert user.hungry? == true
    fed_user = user.feed(Hamburger.new)
    assert fed_user.hungry? == false
    end
    class User
    def initialize(stomach: [])
    @stomach = stomach
    end
    def feed(item)
    User.new(stomach: @stomach + [item])
    end
    end
    

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48. Immutability
    USER
    WALLABY
    .feed
    .feed
    

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49. functional
    Programming
    pure functions
    immutable data
    isolate side-effects
    Compose pipelines of functions
    

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50. Isolate side-effects
    FILE
    DB
    HTTP
    

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51. Isolate side-effects
    FILE
    DB
    HTTP
    

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52. Isolate side-effects
    FILE
    DB
    HTTP
    

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53. functional
    Programming
    pure functions
    immutable data
    isolate side-effects
    Compose pipelines of functions
    

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54. composing side-effects
    web_request
    

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55. composing side-effects
    web_request
    |> transform_request_into_query
    

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56. composing side-effects
    web_request
    |> transform_request_into_query
    |> execute_query
    

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57. composing side-effects
    web_request
    |> transform_request_into_query
    |> execute_query
    |> transform_query_result
    

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58. composing side-effects
    web_request
    |> transform_request_into_query
    |> execute_query
    |> transform_query_result
    |> return_result_to_user
    

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59. composing side-effects
    web_request
    |> transform_request_into_query
    |> execute_query
    |> transform_query_result
    |> return_result_to_user
    Data
    

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60. composing side-effects
    web_request
    |> transform_request_into_query
    |> execute_query
    |> transform_query_result
    |> return_result_to_user
    Pure
    Data
    

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61. composing side-effects
    web_request
    |> transform_request_into_query
    |> execute_query
    |> transform_query_result
    |> return_result_to_user
    Pure
    Impure
    Data
    

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62. Example
    

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63. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    TicketNotifier.new(TicketAlertMailer.new(ticket)).send_alert
    end
    end
    

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64. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    TicketNotifier.new(TicketAlertMailer.new(ticket)).send_alert
    end
    end
    class TicketNotifier
    def initialize(notifier)
    @notifier = notifier
    end
    def send_alert
    OnCallStaff.all.each do |user|
    @notifier.notify(user)
    end
    end
    end
    

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65. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    TicketNotifier.new(TicketAlertMailer.new(ticket)).send_alert
    end
    end
    class TicketNotifier
    def initialize(notifier)
    @notifier = notifier
    end
    def send_alert
    OnCallStaff.all.each do |user|
    @notifier.notify(user)
    end
    end
    end
    class TicketAlertMailer
    def initialize(ticket)
    @ticket
    end
    def self.notify(user)
    email!(user.email, @ticket.id, @ticket.details)
    end
    end
    

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66. Separate arrangement & work
    

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67. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    TicketNotifier.new(TicketAlertMailer.new(ticket)).send_alert
    end
    end
    class TicketNotifier
    def initialize(notifier)
    @notifier = notifier
    end
    def send_alert
    OnCallStaff.all.each do |user|
    @notifier.notify(user)
    end
    end
    end
    class TicketAlertMailer
    def initialize(ticket)
    @ticket
    end
    def notify(user)
    email!(user.email, @ticket.id, @ticket.details)
    end
    end
    

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68. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    TicketNotifier.new(TicketAlertMailer.new(ticket)).send_alert
    end
    end
    class TicketNotifier
    def initialize(notifier)
    @notifier = notifier
    end
    def send_alert
    OnCallStaff.all.each do |user|
    @notifier.notify(user)
    end
    end
    end
    class TicketAlertMailer
    def initialize(ticket)
    @ticket
    end
    def notify(user)
    email!(user.email, @ticket.id, @ticket.details)
    end
    end
    arrangement
    

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69. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    TicketNotifier.new(TicketAlertMailer.new(ticket)).send_alert
    end
    end
    class TicketNotifier
    def initialize(notifier)
    @notifier = notifier
    end
    def send_alert
    OnCallStaff.all.each do |user|
    @notifier.notify(user)
    end
    end
    end
    class TicketAlertMailer
    def initialize(ticket)
    @ticket
    end
    def notify(user)
    email!(user.email, @ticket.id, @ticket.details)
    end
    end
    arrangement
    Work
    

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70. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    TicketNotifier.new(TicketAlertMailer.new(ticket)).send_alert
    end
    end
    class TicketNotifier
    def initialize(notifier)
    @notifier = notifier
    end
    def send_alert
    OnCallStaff.all.each do |user|
    @notifier.notify(user)
    end
    end
    end
    class TicketAlertMailer
    def initialize(ticket)
    @ticket
    end
    def notify(user)
    email!(user.email, @ticket.id, @ticket.details)
    end
    end
    

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71. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    OnCallStaff.all.each do |user|
    TicketNotifier.new(TicketAlertMailer.new(ticket)).send_alert(user)
    end
    end
    end
    class TicketNotifier
    def initialize(notifier)
    @notifier = notifier
    end
    def send_alert(user)
    @notifier.notify(user)
    end
    end
    class TicketAlertMailer
    def initialize(ticket)
    @ticket
    end
    def notify(user)
    email!(user.email, @ticket.id, @ticket.details)
    end
    end
    

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72. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    OnCallStaff.all.each do |user|
    TicketAlertMailer.new(ticket).send_alert(user)
    end
    end
    end
    class TicketAlertMailer
    def initialize(ticket)
    @ticket
    end
    def notify(user)
    email!(user.email, @ticket.id, @ticket.details)
    end
    end
    

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73. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    OnCallStaff.all.each do |user|
    TicketAlertMailer.notify(user, ticket)
    end
    end
    end
    class TicketAlertMailer
    def notify(user, ticket)
    email!(user.email, ticket.id, ticket.details)
    end
    end
    

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74. class NewTicketService
    def self.create_ticket(ticket_params)
    ticket = Ticket.create(ticket_params)
    OnCallStaff.all.each do |user|
    TicketAlertMailer.notify(user, ticket)
    SlackNotifier.notify(user, ticket)
    end
    end
    end
    class TicketAlertMailer
    def notify(user, ticket)
    email!(user.email, ticket.id, ticket.details)
    end
    end
    class SlackNotifier
    def self.notify(user, ticket)
    send_slack_message(user.slack_name, ticket.details)
    end
    end
    

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75. COULD I MAKE THIS
    AN API CALL?
    

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76. COULD I MAKE THIS
    CONCURRENT?
    

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77. COULD I PUT A QUEUE IN
    BETWEEN THESE
    OPERATIONS?
    

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78. Conclusion
    

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79. You don’t have to
    convert all of your
    code to a new
    language.
    

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80. Lets stop making problems for
    ourselves
    

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81. Think about the goals of best
    practices.
    

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82. Build simpler systems
    

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83. Chris Keathley / @ChrisKeathley / keathley@carbonfive.com
    Thanks!
    

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