Functional Object-Oriented Programming

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FUNCTIONAL OBJECT-ORIENTED PROGRAMMING Chris Keathley / @ChrisKeathley / [email protected]

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What this talk isn’t about

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

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

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OO vs FP

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I was trained in this

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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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Java

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What is Object-Oriented Programming?

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

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

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ANIMALS

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ANIMALS BIRDS

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ANIMALS BIRDS DOGS

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How do we use Oop?

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I read lots of books

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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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I Learned best Practices

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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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Un-enforced Best Practices will eventually be violated

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Complexity “CONSISTING OF MANY DIFFERENT AND CONNECTED PARTS”

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Simple “COMPOSED OF A SINGLE ELEMENT.”

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Decoupling

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Complexity is the death of productivity

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

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OOP is complex By Nature

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Encapsulation STATE BEHAVIOR

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Inheritance ANIMALS BIRDS

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Inheritance ANIMALS BIRDS

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State FOO BAR BAZ

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State FOO BAR BAZ ME

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State FOO BAR BAZ ME Foo

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State FOO BAR BAZ ME Foo Bar

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State FOO BAR BAZ ME Foo Baz Bar

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Methods FOO STATE PRIVATE METHOD PRIVATE METHOD

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I combat complexity with Functional Programming

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

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

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

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Pure Functions Have no side effects FS DB +

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

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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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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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Immutability USER WALLABY .feed .feed

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

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Isolate side-effects FILE DB HTTP

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Isolate side-effects FILE DB HTTP

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Isolate side-effects FILE DB HTTP

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

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composing side-effects web_request

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composing side-effects web_request |> transform_request_into_query

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composing side-effects web_request |> transform_request_into_query |> execute_query

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

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

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

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

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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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Example

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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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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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Separate arrangement & work

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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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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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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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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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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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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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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