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
2. What this talk isn’t about
3. “OO IS EVIL!!!” - People on the internet
4. “OO IS EVIL!!!” - People on the internet Kthnxbye
5. OO vs FP
6. I was trained in this
7. C
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 : '(' <expr>* ')' ; \ qexpr : '{' <expr>* '}' ; \ expr : <number> | <symbol> | <sexpr> ; \ lispy : /^/ <expr>* /$/ ; \ ", Number, Symbol, Sexpr, Qexpr, Expr, Lispy); puts("Crisp Version 0.0.0.1"); puts("Press Ctrl+c to Exit\n"); while (1) { char* input = readline("crisp> "); add_history(input); mpc_result_t r; if (mpc_parse("<stdin>", input, Lispy, &r)) { lval* x = lval_eval(lval_read(r.output)); lval_println(x); lval_del(x); mpc_ast_delete(r.output); } else { mpc_err_print(r.error); mpc_err_delete(r.error);
9. int main(int argc, char** argv) { mpc_parser_t* Number = mpc_new("number"); mpc_parser_t* Symbol = mpc_new("symbol"); mpc_parser_t* Sexpr = mpc_new("sexpr"); mpc_parser_t* Qexpr = mpc_new("qexpr"); mpc_parser_t* Expr = mpc_new("expr"); mpc_parser_t* Lispy = mpc_new("lispy"); mpca_lang(MPC_LANG_DEFAULT, " \ number : /-?[0-9]+/ ; \ symbol : '+' | '-' | '*' | '/' ; \ sexpr : '(' <expr>* ')' ; \ qexpr : '{' <expr>* '}' ; \ expr : <number> | <symbol> | <sexpr> ; \ lispy : /^/ <expr>* /$/ ; \ ", 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("<stdin>", 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
10. Java
11. What is Object-Oriented Programming?
12. OBJECT ORIENTED LANGUAGES HAVE… ▸ Behavior + Data (encapsulation) ▸ Classes ▸ Objects (instances of classes) ▸ Inheritance ▸ Methods ▸ Polymorphism
13. OBJECT ORIENTED PROGRAMMING IMPLIES… ▸ State ▸ Mutability ▸ Encapsulation ▸ Domain modeling ▸ Message passing
14. ANIMALS
15. ANIMALS BIRDS
16. ANIMALS BIRDS DOGS
17. How do we use Oop?
18. I read lots of books
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
20. I Learned best Practices
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
22. Un-enforced Best Practices will eventually be violated
23. Complexity “CONSISTING OF MANY DIFFERENT AND CONNECTED PARTS”
24. Simple “COMPOSED OF A SINGLE ELEMENT.”
25. Decoupling
26. Complexity is the death of productivity
27. “the first 90% of all software products is the MVP, the other 90% is maintenance” - Greg O.
28. OOP is complex By Nature
29. Encapsulation STATE BEHAVIOR
30. Inheritance ANIMALS BIRDS
31. Inheritance ANIMALS BIRDS
32. State FOO BAR BAZ
33. State FOO BAR BAZ ME
34. State FOO BAR BAZ ME Foo
35. State FOO BAR BAZ ME Foo Bar
36. State FOO BAR BAZ ME Foo Baz Bar
37. Methods FOO STATE PRIVATE METHOD PRIVATE METHOD
38. I combat complexity with Functional Programming
39. functional Programming pure functions immutable data isolate side-effects Compose pipelines of functions
40. functional Programming pure functions immutable data isolate side-effects Compose pipelines of functions
41. Pure Functions (+2) 3 5 Always return the same result given the same arguments
42. Pure Functions Have no side effects FS DB +
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
44. functional Programming pure functions immutable data isolate side-effects Compose pipelines of functions
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
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
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
48. Immutability USER WALLABY .feed .feed
49. functional Programming pure functions immutable data isolate side-effects Compose pipelines of functions
50. Isolate side-effects FILE DB HTTP
51. Isolate side-effects FILE DB HTTP
52. Isolate side-effects FILE DB HTTP
53. functional Programming pure functions immutable data isolate side-effects Compose pipelines of functions
54. composing side-effects web_request
55. composing side-effects web_request |> transform_request_into_query
56. composing side-effects web_request |> transform_request_into_query |> execute_query
57. composing side-effects web_request |> transform_request_into_query |> execute_query |> transform_query_result
58. composing side-effects web_request |> transform_request_into_query |> execute_query |> transform_query_result |> return_result_to_user
59. composing side-effects web_request |> transform_request_into_query |> execute_query |> transform_query_result |> return_result_to_user Data
60. composing side-effects web_request |> transform_request_into_query |> execute_query |> transform_query_result |> return_result_to_user Pure Data
61. composing side-effects web_request |> transform_request_into_query |> execute_query |> transform_query_result |> return_result_to_user Pure Impure Data
62. Example
63. class NewTicketService def self.create_ticket(ticket_params) ticket = Ticket.create(ticket_params) TicketNotifier.new(TicketAlertMailer.new(ticket)).send_alert end end
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
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
66. Separate arrangement & work
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
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
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
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
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
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
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
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
75. COULD I MAKE THIS AN API CALL?
76. COULD I MAKE THIS CONCURRENT?
77. COULD I PUT A QUEUE IN BETWEEN THESE OPERATIONS?
78. Conclusion
79. You don’t have to convert all of your code to a new language.
80. Lets stop making problems for ourselves
81. Think about the goals of best practices.
82. Build simpler systems
83. Chris Keathley / @ChrisKeathley / keathley@carbonfive.com Thanks!