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clean code from theory to practice by Luís Zamith

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Clean Code TAKING YOUR PROGRAMS TO THE LAUNDRY

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No content

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1. Looks like you cared

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1. Looks like you cared 2. Pretty much what you expected

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1. Looks like you cared 2. Pretty much what you expected 3. Language looks as perfect fit for problem

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1. Looks like you cared 2. Pretty much what you expected 3. Language looks as perfect fit for problem My definition

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circular friction reduction device with central axis

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circular friction reduction device with central axis =

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Design Patterns circular friction reduction device with central axis =

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class Report def initialize @title = 'Monthly Report' @text = [ 'Things are going', 'really, really well.' ] end ! def output_report ...HTML specific stuff... end end template method: reports

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bad code class Report def initialize @title = 'Monthly Report' @text = [ 'Things are going', 'really, really well.' ] end ! def output_report ...HTML specific stuff... end end template method: reports

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template method: reports class Report def initialize @title = 'Monthly Report' @text = ['Things are going', 'really, really well.'] end ! def output_report output_start output_head @text.each do |line| output_line(line) end output_end end ! def output_start; end ! def output_head output_line(@title) end ! def output_line(line) raise 'Called abstract method: output_line' end ! def output_end; end end

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template method: reports better code class Report def initialize @title = 'Monthly Report' @text = ['Things are going', 'really, really well.'] end ! def output_report output_start output_head @text.each do |line| output_line(line) end output_end end ! def output_start; end ! def output_head output_line(@title) end ! def output_line(line) raise 'Called abstract method: output_line' end ! def output_end; end end

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Design Principles THE THEORY BEHIND THE THEORY

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Optimize for Readability and Maintainability

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S O L I D Uncle Bob Martin

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S O L I D ingle responsibility Uncle Bob Martin

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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class TokenizedModel < SimpleDelegator! def save! __getobj__.token ||= SecureRandom.urlsafe_base64! __getobj__.save! end! ! def to_param! __getobj__.token! end! end TokenizedModel.new(invitation) Decorator Pattern

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def deliver! Mailer.invitation_notification(self).deliver! end! end

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Responsibility = Reason to Change

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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class Invitation < ActiveRecord::Base! EMAIL_REGEX = /\A([^@\s]+)@((:?[a-z0-9]+\.)+[a-z]{2,})\z/i! STATUSES = %w(pending accepted)! ! belongs_to :sender, class_name: 'User'! belongs_to :survey! ! before_create :set_token! ! validates :recipient_email, presence: true, format: EMAIL_REGEX! validates :status, inclusion: { in: STATUSES }! ! def to_param! token! end! ! def deliver! Mailer.invitation_notification(self).deliver! end! ! private! ! def set_token! self.token = SecureRandom.urlsafe_base64! end! end

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S O L I D

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S O L I D pen closed

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# does not follow OCP! class Purchase! def charge_user!! Stripe.charge(user: user, amount: amount)! end! end

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# does not follow OCP! class Purchase! def charge_user!! Stripe.charge(user: user, amount: amount)! end! end # follows OCP by depending on an abstraction! class Purchase! def charge_user!(payment_processor)! payment_processor.charge(user: user, amount: amount)! end! end

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class Printer! def initialize(item)! @item = item! end! ! def print! thing_to_print = case @item! when Text! @item.to_s! when Image! @item.filename! when Document! @item.formatted! end! ! send_to_printer(thing_to_print)! end! end

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class Printer! def initialize(item)! @item = item! end! ! def print! send_to_printer(@item.printable_representation)! end! end Dependency Injection

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# does not follow OCP! class Unsubscriber! def unsubscribe!! SubscriptionCanceller.new(user).process! CancellationNotifier.new(user).notify! CampfireNotifier.announce_sad_news(user)! end! end

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class UnsubscriptionCompositeObserver! def initialize(observers)! @observers = observers! end! ! def notify(user)! @observers.each do |observer|! observer.notify(user)! end! end! end! ! class Unsubscriber! def initialize(observer)! @observer = observer! end! ! def unsubscribe!(user)! observer.notify(user)! end! end Composite Pattern

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class UnsubscriptionCompositeObserver! def initialize(observers)! @observers = observers! end! ! def notify(user)! @observers.each do |observer|! observer.notify(user)! end! end! end! ! class Unsubscriber! def initialize(observer)! @observer = observer! end! ! def unsubscribe!(user)! observer.notify(user)! end! end Observer Pattern

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class UnsubscriptionCompositeObserver! def initialize(observers)! @observers = observers! end! ! def notify(user)! @observers.each do |observer|! observer.notify(user)! end! end! end! ! class Unsubscriber! def initialize(observer)! @observer = observer! end! ! def unsubscribe!(user)! observer.notify(user)! end! end

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A word of caution

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S O L I D

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S O L I D iskov substitution

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Let q(x) be a property provable about objects x of type T. Then q(y) should be provable for objects y of type S where S is a subtype of T. “

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blah q(x) blah blah blah blah blah blah blah blah x blah T. Blah q(y) blah blah blah blah blah blah y blah blah S blah S blah blah blah blah T. “

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class Signup! def initialize(attributes)! @attributes = attributes! end! ! def save! account = Account.create!(@attributes[:account])! account.users.create!(@attributes)! end! end! ! class SignupsController < ApplicationController! def create! build_signup.save! end! ! def build_signup! Signup.new(params[:signup])! end! end

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A wild requirement appears…

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class InvitationSignup < Signup! def save(invitation)! user = super! invitation.accept(user)! user! end! end A wild requirement appears…

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class SignupsController < ApplicationController! def create! signup = build_signup! if params[:invitation_id]! invitation = Invitation.find(params[:invitation_id])! signup.save(invitation)! else! signup.save! end! end! ! def build_signup! if params[:invitation_id]! InvitationSignup.new(params[:signup])! else! Signup.new(params[:signup])! end! end! end

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class SignupsController < ApplicationController! def create! signup = build_signup! if params[:invitation_id]! invitation = Invitation.find(params[:invitation_id])! signup.save(invitation)! else! signup.save! end! end! ! def build_signup! if params[:invitation_id]! InvitationSignup.new(params[:signup])! else! Signup.new(params[:signup])! end! end! end

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def InvitationSignup < Signup! def initialize(attributes, invitation)! super(attributes)! @invitation = invitation! end! ! def save! user = super! @invitation.accept(user)! user! end! end The public API remains the same

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class SignupsController < ApplicationController! def create! build_signup.save! end! ! def build_signup! if params[:invitation_id]! InvitationSignup.new(params[:signup])! else! Signup.new(params[:signup])! end! end! end

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S O L I D

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S O L I D nterface segragation

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public class WebPage implements IWebPage {! public String currentUrl() {};! public void setUrl(String url) {};! public String[] consoleMessages() {};! public String[] alertMessages() {};! public String[] confirmMessages() {};! public String[] promptMessages() {};! }

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public class WebPage implements IWebPage {! public String currentUrl() {};! public void setUrl(String url) {};! public String[] consoleMessages() {};! public String[] alertMessages() {};! public String[] confirmMessages() {};! public String[] promptMessages() {};! } Not all methods are related

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public class VisitCommand {! public VisitCommand(WebPage page, String url) {! this.page = page;! this.url = url;! }! ! public void start() {! page.setUrl(url)! }! ! private WebPage page;! private String url;! } Command Pattern

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public interface HasUrl {! public String currentUrl() {};! public void setUrl(String url) {};! }! ! public interface HasMessages {! public String[] consoleMessages() {};! public String[] alertMessages() {};! public String[] confirmMessages() {};! public String[] promptMessages() {};! } public class WebPage implements HasUrl, HasMessages {

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public class VisitCommand {! public VisitCommand(HasUrl page, String url) {! this.page = page;! this.url = url;! }! ! public void start() {! page.setUrl(url)! }! ! private HasUrl page;! private String url;! }

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public class VisitCommand {! public VisitCommand(HasUrl page, String url) {! this.page = page;! this.url = url;! }! ! public void start() {! page.setUrl(url)! }! ! private HasUrl page;! private String url;! }

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http://tenderlovemaking.com/2014/06/02/yagni-methods-are-killing-me.html loop do params[:foo] params.delete :foo params[:foo] = [Object.new] end def convert_value_to_parameters(value) if value.is_a?(Array) && !converted_arrays.member?(value) converted = value.map { |_| convert_value_to_parameters(_) } converted_arrays << converted converted elsif value.is_a?(Parameters) || !value.is_a?(Hash) value else self.class.new(value) end end

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merge! delete_if keep_if select! reject!

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S O L I D

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S O L I Dependency inversion

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“High level modules should not depend on low level modules, they should both depend on abstractions

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#Violates DIP! class Copier! def self.copy! reader = KeyboardReader.new! writer = Printer.new! ! keystrokes = reader.read_until_eof! writer.write(keystrokes)! end! end

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#Obeys DIP. Is decoupled and reusable.! class Copier! def initialize(reader, writer)! @reader = reader! @writer = writer! end! ! def copy! keystrokes = @reader.read_until_eof! @writer.write(keystrokes)! end! end! ! Copier.new(KeyboardReader.new, Printer.new)! Copier.new(KeyboardReader.new, NetworkPrinter.new)

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class NetworkPrinterAdapter! def initialize(network_printer)! @network_printer = network_printer! end! ! def write(keystrokes)! @network_printer.print(keystrokes)! end! end! ! network_printer = ! NetworkPrinterAdapter.new(NetworkPrinter.new)! Copier.new(KeyboardReader.new, network_printer) Adapter Pattern

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class Product < ActiveRecord::Base! has_many :purchases! end! ! class Purchase < ActiveRecord::Base! belongs_to :Product! ! def has_receipt?! receipt.present?! end! ! def receipt_id! receipt.id! end! ! def receipt_address! receipt.details.address! end! ! private! ! def receipt! Stripe::Receipt.find(stripe_order_id)! end! end

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class PurchaseWithReceipt < SimpleDelegator! def initialize(purchase, receipt_finder)! super(purchase)! @receipt_finder = receipt_finder! end! ! def has_receipt?! receipt.present?! end! ! def receipt_id! receipt.id! end! ! def receipt_address! receipt.details.address! end! ! private! ! def receipt! @receipt_finder.find(stripe_order_id)! end! end class Product < ActiveRecord::Base! has_many :purchases! end! ! class Purchase < ActiveRecord::Base! belongs_to :product! end

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S O L I D ingle responsibility pen closed iskov substitution nterface segragation ependency inversion Uncle Bob Martin

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RECAP DESIGN PRINCIPLES DESIGN PATTERNS + = CLEAN CODE

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Code Smells Sir, your issues have some code.

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long method Smell number 1

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Can’t tell what it does at a glance, it’s

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Can’t tell what it does at a glance, it’s TOO LONG

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Can’t tell what it does at a glance, it’s TOO LONG More than one level of nesting, probably

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Can’t tell what it does at a glance, it’s TOO LONG More than one level of nesting, probably TOO LONG

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Can’t tell what it does at a glance, it’s TOO LONG More than one level of nesting, probably TOO LONG More than one level of abstraction, may be

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Can’t tell what it does at a glance, it’s TOO LONG More than one level of nesting, probably TOO LONG TOO LONG More than one level of abstraction, may be

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Can’t tell what it does at a glance, it’s TOO LONG More than one level of nesting, probably TOO LONG TOO LONG More than one level of abstraction, may be More than 5 lines

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Can’t tell what it does at a glance, it’s TOO LONG More than one level of nesting, probably TOO LONG TOO LONG More than one level of abstraction, may be More than 5 lines TOO LONG

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Can’t tell what it does at a glance, it’s TOO LONG More than one level of nesting, probably TOO LONG TOO LONG More than one level of abstraction, may be More than 5 lines TOO LONG REFACTOR

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Extract Method: Split method into many auxiliary methods Solution #1

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Replace temp with query: Move local variables into methods Solution #2

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large class Smell number 2

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No content

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Need to scroll to know what it does, it’s

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Need to scroll to know what it does, it’s TOO BIG

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Need to scroll to know what it does, it’s TOO BIG More private methods than public, it’s

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Need to scroll to know what it does, it’s TOO BIG More private methods than public, it’s TOO BIG

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Need to scroll to know what it does, it’s TOO BIG More private methods than public, it’s TOO BIG More than seven methods, probably

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Need to scroll to know what it does, it’s TOO BIG More private methods than public, it’s TOO BIG TOO BIG More than seven methods, probably

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Need to scroll to know what it does, it’s TOO BIG More private methods than public, it’s TOO BIG TOO BIG More than seven methods, probably More than 100 lines

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Need to scroll to know what it does, it’s TOO BIG More private methods than public, it’s TOO BIG TOO BIG More than seven methods, probably More than 100 lines TOO BIG

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Need to scroll to know what it does, it’s TOO BIG More private methods than public, it’s TOO BIG TOO BIG More than seven methods, probably More than 100 lines TOO BIG REFACTOR

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Extract class: If the class has multiple responsibilities Solution #1

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Extract decorator: If the class has many objects related to a single action Solution #2

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class Report def initialize @title = 'Monthly Report' @text = [ 'Things are going', 'really, really well.' ] end ! def output_report ...HTML specific stuff... end end strategy pattern: reports

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bad code class Report def initialize @title = 'Monthly Report' @text = [ 'Things are going', 'really, really well.' ] end ! def output_report ...HTML specific stuff... end end strategy pattern: reports

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class Report def initialize(formatter) @title = 'Monthly Report' @text = [ 'Things are going', 'really, really well.' ] @formatter = formatter.new(@title, @text) end ! def formatter=(formatter) @formatter = formatter.new(@title, @text) end ! def output_report @formatter.output_report end end strategy pattern: reports

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class Report def initialize(formatter) @title = 'Monthly Report' @text = [ 'Things are going', 'really, really well.' ] @formatter = formatter.new(@title, @text) end ! def formatter=(formatter) @formatter = formatter.new(@title, @text) end ! def output_report @formatter.output_report end end better code strategy pattern: reports

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strategy pattern: reports report = Report.new(HTMLFormatter) report.output_report ! report.formatter = PlainTextFormatter report.output_report

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beware of the god class

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feature envy Smell number 3 All your features are mine

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Smelling feature envy: 4SYMPTOMS

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Smelling feature envy: Many references to the same object

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Smelling feature envy: Local variables or params that are used more than instance variables and methods

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Smelling feature envy: Methods that include a class name in their name

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Smelling feature envy: Private methods on the same class with the same parameter

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Smelling feature envy: class Completion! def score! answers.inject(0) do |result, answer|! question = answer.question! result + question.score(answer.text)! end! end! end

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Extract method: If possible move part of a method to the appropriate class Solution #1

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Move method: Move the entire method into the right class Solution #2

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Solving feature envy: class Answer! def score! question.score(text)! end! end! ! class Completion! answers.inject(0) do |result, answer|! result + answer.score! end! end

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DESIGN PRINCIPLES DESIGN PATTERNS + = CLEAN CODE

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missing some style

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Learn the principles patterns Know the use the smells

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BLEEDING EDGE

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Hexagonal Architecture Domain Driven Design (DDD) Presenters Service Objects Value Objects and Immutability Behavior Driven Development (BDD) Object Composition vs Inheritance

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Practical Object-Oriented Design in Ruby

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Practical Object-Oriented Design in Ruby Growing Object-Oriented Software

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Practical Object-Oriented Design in Ruby Growing Object-Oriented Software Test-Driven Development

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Practical Object-Oriented Design in Ruby Growing Object-Oriented Software Test-Driven Development Clean Code

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thanks!