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Architecting is Difficult @Jack_Franklin

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Any fool can write code that a computer can understand. Good programmers write code that humans can understand. ! Martin Fowler [@martinfowler]

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What makes code difficult to work with?

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YMMV

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you’re never going to get it perfect first time

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Defer concrete decisions as late as possible - you'll never again know less about the problem than you do right now and the correct abstraction will become clearer over time. ! Andy Appleton [@appltn]

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writing good code improving existing code

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Writing Good Code: Tests

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drive your API design

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difficult to test == difficult to use

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confidence when refactoring (but we’ll come back to this later)

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Writing Good Code: Naming Conventions

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There are only two hard things in Computer Science: cache invalidation and naming things. ! Phil Karlton

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There are only two hard things in Computer Science: cache invalidation, naming things and off by one errors. ! ???

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prefer verbosity

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be consistent use the same nouns and verbs

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Writing Good Code: Coding Standards

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editorconfig.org

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actual standard is irrelevant pick one and stick to it

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Writing Good Code: Single Responsibility

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do one thing and do it well

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Not one thing well class EmailSender def initialize(csv) ! def parse_csv_for_emails ! def send_email end

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Better class EmailSender def initialize(csv) def parse_csv_for_emails Parser.new(csv).emails def send_email end ! class Parser def initialize(csv) def emails end

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Writing Good Code: Decoupled Components

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class EmailSender def initialize(csv) def parse_csv_for_emails Parser.new(csv).emails def send_email end ! class Parser def initialize(csv) def emails end This knowledge isn’t needed here

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class EmailSender def initialize(emails) def send_email end ! class Parser def initialize(csv) def emails end ! emails = Parser.new(csv).emails EmailSender.new(emails).send_email knows how to send an email to an array of emails knows how to parse a CSV and get the email addresses

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Writing Good Code: Separate Aggressively

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don’t be afraid to create classes / objects

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easier to merge two tiny classes than split up one massive one

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Refactoring

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No content

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Refactoring: alter code without changing behaviour

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you have to have tests!

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Code Smells

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Code Smell: some code which may indicate a problem

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You don’t fix code smells. You look at them and see if they indicate a problem you can fix. ! Joe Ferris [@joe_ferris]

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class SomeMapThing def initialize(x, y) end ! class LatLong def self.get_lat_long(x, y) end ! class User def coords [x, y] end

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data clumps continually passing round two objects as arguments

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class SomeMapThing def initialize(coords) ! class LatLong def self.get_lat_long(coords) ! class User def coords ! class Coords def x def y ! coords = Coords.new(2, 3) LatLong.get_lat_long(coords)

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if two arguments are tightly related, encapsulate that knowledge

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class GraphDrawer def draw width = 165 + bar_width height = 170.2 + bar_height … end

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why 165? why 170.2? This is very common in JavaScript / jQuery code, and CSS too.

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class GraphDrawer GRAPH_HEIGHT_PADDING = 170.2 GRAPH_WIDTH_PADDING = 165 def draw width = GRAPH_WIDTH_PADDING * bar_width height=GRAPH_HEIGHT_PADDING + bar_height end

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no knowledge should be left in your head

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<% if user != nil %>

<%= user.welcome_message %>

<% else %>

Please sign in

<% end %>

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checking for nil / undefined

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what does nil mean? no first name? system error? no name yet? no user logged in?

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implicit knowledge in a codebase is bad

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class NullUser def welcome_message “Please sign in” end ! user = current_user || NullUser.new

<%= user.welcome_message %>

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don’t check for nil

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def check_for_overheating(system_monitor) if system_monitor.temperature > 100 system_monitor.sound_alarms end end

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def check_for_overheating(system_monitor) if system_monitor.temperature > 100 system_monitor.sound_alarms end end

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tell, don’t ask http://robots.thoughtbot.com/tell-dont-ask

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system_monitor.check_for_overheating ! class SystemMonitor def check_for_overheating if temperature > 100 sound_alarms end end end

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we’re now telling the object what to do rather than asking it if it can do it

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coupling http://robots.thoughtbot.com/types-of-coupling

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def save(should_run_validations=true) if should_run_validations validate store else store ! # in our app, everywhere user.save post.save(false)

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control coupling

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if I update the save method every usage of the method has to change

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(this actually happened in Rails)

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better solution would be to split the methods up

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you have to have some coupling, else nothing could talk to anything

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“If I change this method, how many changes do I have to make else where?”

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Publish and Subscribe

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class ModuleA def init(b) def a_thing do_a_thing b.do_thing ! ! class ModuleB def do_thing # has to happen after ModuleA#a_thing

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Module A knows too much

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class ModuleA def init(event) def a_thing do_a_thing event.publish(‘a_thing_complete’) ! ! class ModuleB def init(event) event.subscribe(‘a_thing_complete’) { do_thing } ModuleA doesn’t know (or care) what modules listen to a_thing_complete

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Now no module knows about the other

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class ModuleA def init(event) def a_thing do_a_thing event.publish(‘a_thing_complete’) ! class ModuleB … class ModuleC def init(event) event.subscribe(‘a_thing_complete’) { do_thing }

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class User def posts_by_user blog.posts.where(user_id: id) end

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The Law of Demeter

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It’s an actual law!

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A method of an object should only invoke only the methods of the following kinds of objects: ! 1. itself 2. its parameters 3. any objects it creates 4. its direct component objects

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class User def posts_by_user blog.posts.where(user_id: id) end multiple dots

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class User def posts_by_user blog.posts_by_user(id) end ! class Blog def posts_by_user(id) posts.where(user_id: id) end

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avoid duplication of knowledge across your system

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OK, so it’s not an actual law

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Approaches to maintaining code

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Every time you work with some code, leave it a tiny bit better than when you left it

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don’t ignore a problem or leave #FIXME comments

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#todo: this entire class is screwed, fix it

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if you need to make the change, but the change is difficult

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first refactor to make the change easy then make the change!

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you can’t get it right first time every time

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keep friction to running tests low

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because then you’ll run them

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code reviews

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http://robots.thoughtbot.com/ ! https://speakerdeck.com/jackfranklin ! http://refactoring.com/

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Thanks! javascriptplayground.com @Jack_Franklin