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The Missing System Or Preparing for Piecemeal Growth

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Jim Gay @saturnflyer ! clean-ruby.com clean-ruby.com/dsl

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Jim Gay @saturnflyer ! github.com/saturnflyer/surrounded

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Habitability & Barriers

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Patterns of Software

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–Richard Gabriel Habitability is the characteristic of source code 
 that enables programmers,
 
 to understand its construction and intentions, and to change it comfortably and confidently.

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–Richard Gabriel Habitability is the characteristic of source code that enables programmers, coders, bug-fixers, and people coming to the code later in its life to understand its construction and intentions, and to change it comfortably and confidently.

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class Person! def display_address! "".tap do |string|! if !address.street.nil? || !address.street.empty?! string << address.street! end! ! string << "\n" unless string.empty?! ! if !address.city.nil? address.city.empty? || address.city.nil?! string << address.city! end! ! if address.province || address.postal_code! string << ", "! end! ! if address.province || address.postal_code! if address.province! string << address.province! end! ! string << " "! ! if address.postal_code! string << address.postal_code!

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! ! ! ! ! ! ! ! ! ! ! ! class Template! def display(address)! region = [address.province, address.postal_code].compact.join(' ')! region = nil if region.empty?! ! city_region = [address.city, region].compact.join(', ')! city_region = nil if city_region.empty?! ! STDOUT.puts [address.street, city_region].compact.join("\n")! end! end

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! ! ! ! ! ! class Address! def display(template)! template.display(self)! end! end! ! class Template! def display(address)! region = [address.province, address.postal_code].compact.join(' ')! region = nil if region.empty?! ! city_region = [address.city, region].compact.join(', ')! city_region = nil if city_region.empty?! ! STDOUT.puts [address.street, city_region].compact.join("\n")! end! end

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class Person! def display_address(template=Template.new)! address.display(template)! end! end! ! class Address! def display(template)! template.display(self)! end! end! ! class Template! def display(address)! region = [address.province, address.postal_code].compact.join(' ')! region = nil if region.empty?! ! city_region = [address.city, region].compact.join(', ')! city_region = nil if city_region.empty?! ! STDOUT.puts [address.street, city_region].compact.join("\n")! end! end

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person.display_address(template)! ! address.display(template)! ! template.display(address)! ! STDOUT.puts “…”! Tell Don’t Ask

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–Christopher Alexander It is simply not possible to fix today what the environment should be like [in the future], and then to steer the piecemeal process of development toward that fixed, imaginary world.

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–Richard Gabriel ! ! 
 Bugs tell us that we are not capable of producing a master plan.

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–Richard Gabriel Many a bug is the result of not anticipating a particular event or use and is not the result of a mistake—bugs are not always errors. 
 Bugs tell us that we are not capable of producing a master plan.

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github.com/saturnflyer/surrounded

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Goals • Preserve existing object behavior / allow extension • Localize use case behavior • Apply behavior only when necessary

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Goals • Preserve existing object behavior / allow extension • Localize use case behavior • Apply behavior only when necessary

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class UserActivation! def initialize(admin, user)! @admin = admin! @user = user! end! attr_reader :admin, :user! private :admin, :user! end

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class UserActivation! def initialize(admin, user)! @admin = admin.extend(Admin)! @user = user! end! attr_reader :admin, :user! private :admin, :user! ! module Admin! #…! end! end

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class UserActivation! def initialize(admin, user)! @admin = Admin.new(admin)! @user = user! end! attr_reader :admin, :user! private :admin, :user! ! class Admin! #…! end! end class UserActivation! def initialize(admin, user)! @admin = admin.extend(Admin)! @user = user! end! attr_reader :admin, :user! private :admin, :user! ! module Admin! #…! end! end

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class UserActivation! def initialize(admin, user)! @admin = admin! @user = user! map_roles([:admin, :user].zip([admin, user]))! end! attr_reader :admin, :user! private :admin, :user! ! module Admin! #…! end! end

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class UserActivation! def initialize(admin, user)! @admin = admin! @user = user! map_roles([[:admin, admin], [:user, user]])! end! attr_reader :admin, :user! private :admin, :user! ! module Admin! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! module Admin! #…! end! end

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module Surrounded! module Context! module Initializing! def initialize(*setup_args)! attr_reader(*setup_args)! private(*setup_args)! mod = Module.new! line = __LINE__; mod.class_eval "! def initialize(#{setup_args.join(',')})! map_roles(#{setup_args.to_s}.zip(! ! ! ! ! [#{setup_args.join(‘,')}]! ! ! ! ))! end! ", __FILE__, line! const_set("ContextInitializer", mod)! include mod! end! end! end! end

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module Surrounded! module Context! module Initializing! def initialize(*setup_args)! attr_reader(*setup_args)! private(*setup_args)! mod = Module.new! line = __LINE__; mod.class_eval "! def initialize(#{setup_args.join(',')})! map_roles(#{setup_args.to_s}.zip(! ! ! ! ! [#{setup_args.join(‘,')}]! ! ! ! ))! end! ", __FILE__, line! const_set("ContextInitializer", mod)! include mod! end! end! end! end

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module Surrounded! module Context! module Initializing! def initialize(*setup_args)! attr_reader(*setup_args)! private(*setup_args)! mod = Module.new! line = __LINE__; mod.class_eval "! def initialize(#{setup_args.join(',')})! map_roles(#{setup_args.to_s}.zip(! ! ! ! ! [#{setup_args.join(‘,')}]! ! ! ! ))! end! ", __FILE__, line! const_set("ContextInitializer", mod)! include mod! end! end! end! end

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module Surrounded! module Context! module Initializing! def initialize(*setup_args)! attr_reader(*setup_args)! private(*setup_args)! mod = Module.new! line = __LINE__; mod.class_eval "! def initialize(#{setup_args.join(',')})! map_roles(#{setup_args.to_s}.zip(! ! ! ! ! [#{setup_args.join(‘,')}]! ! ! ! ))! end! ", __FILE__, line! const_set("ContextInitializer", mod)! include mod! end! end! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! module Admin! #…! end! end

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class UserActivation! def initialize(admin, user)! @admin = admin.extend(Admin)! @user = user! map_roles([[:admin,admin], [:user, user]])! end! attr_reader :admin, :user! private :admin, :user! ! module Admin! #…! end! end

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class UserActivation! def initialize(admin, user)! @admin = admin.extend(Admin)! @user = user! map_roles([[:admin,admin], [:user, user]])! special_processing(…)! end! attr_reader :admin, :user! private :admin, :user! ! module Admin! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! def initialize(admin, user)! super! special_processing(…)! end! ! ! module Admin! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! def initialize(admin, user)! super! special_processing(…)! end! ! ! module Admin! #…! end! end

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module Surrounded! module Context! module Initializing! def initialize(*setup_args)! attr_reader(*setup_args)! private(*setup_args)! mod = Module.new! line = __LINE__; mod.class_eval "! def initialize(#{setup_args.join(',')})! map_roles(#{setup_args.to_s}.zip(! ! ! ! ! [#{setup_args.join(‘,')}]! ! ! ! ))! end! ", __FILE__, line! const_set("ContextInitializer", mod)! include mod! end! end! end! end

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module Surrounded! module Context! module Initializing! def initialize(*setup_args)! attr_reader(*setup_args)! private(*setup_args)! mod = Module.new! line = __LINE__; mod.class_eval "! def initialize(#{setup_args.join(',')})! map_roles(#{setup_args.to_s}.zip(! ! ! ! ! [#{setup_args.join(‘,')}]! ! ! ! ))! end! ", __FILE__, line! const_set("ContextInitializer", mod)! include mod! end! end! end! end UserActivation ContextInitializer #initialize #initialize Object Kernel BasicObject

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! module Admin! #…! end! end

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Goals • Preserve existing object behavior / allow extension • Localize use case behavior • Apply behavior only when necessary

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Coupling & Cohesion

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–Richard Gabriel The primary feature for easy maintenance is locality !

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–Richard Gabriel The primary feature for easy maintenance is locality: Locality is that characteristic of source code that enables a programmer to understand that source by looking at only a small portion of it.

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! module Admin! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! module Admin! #…! end! end class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! class Admin < SimpleDelegator! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! role :admin do! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! role :admin, :module do! #…! end! end class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! role :admin, :wrapper do! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! module Admin! #…! end! end class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! role :admin, :wrapper do! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! role :admin, :module do! #…! end! end class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! class Admin < ::MyWrapper! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! role :admin do! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! role :admin do! #…! end! end! ! UserActivation::Admin ! # => NameError: private constant UserActivation::Admin referenced class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! module Admin! #…! end! private_constant :Admin! end

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Goals • Preserve existing object behavior / allow extension • Localize use case behavior • Apply behavior only when necessary

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! def do_something! # use objects and role behaviors! end! ! ! ! ! ! role :admin do! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! def do_something! apply_behaviors! # use objects and role behaviors! ensure ! remove_behaviors! end! ! ! role :admin do! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! trigger :do_something do! # use objects and role behaviors! end! ! ! ! ! ! role :admin do! #…! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! trigger :do_something do! # use objects and role behaviors! end! ! ! ! ! ! role :admin do! #…! end! end! ! ! ! UserActivation.new(user1, user2).triggers! # => [:do_something]

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! trigger :do_something do! # use objects and role behaviors! end! ! def non_trigger! # do something, roles not applied! end! ! role :admin do! #…! end! end! ! ! ! UserActivation.new(user1, user2).triggers! # => [:do_something]! UserActivation.new(user1, user2).methods! # => [:do_something, :non_trigger, …]

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! trigger :do_something do! admin.perform_action(user)! end! ! ! ! ! ! role :admin do! def perform_action(user)! # …! end! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user, :notifier! ! trigger :do_something do! admin.perform_action(user, notifier)! end! ! ! ! ! ! role :admin do! def perform_action(user, notifier)! # …! end! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user, :notifier, :listener! ! trigger :do_something do! admin.perform_action(user, notifier, listener)! end! ! ! ! ! ! role :admin do! def perform_action(user, notifier, listener)! # …! end! end! end

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class UserActivation! extend Surrounded::Context! ! initialize :admin, :user, :notifier, :listener! ! trigger :do_something do! admin.perform_action! end! ! ! ! ! ! role :admin do! def perform_action! # has access to:! user! notifier! listener! end! end! end

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module Surrounded! ! def method_missing(meth, *args, &block)! context.role?(meth){} || super! end! ! def respond_to_missing?(meth, include_private=false)! !!context.role?(meth){} || super! end! ! end

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module Surrounded! ! def method_missing(meth, *args, &block)! context.role?(meth){} || super! end! ! def respond_to_missing?(meth, include_private=false)! !!context.role?(meth){} || super! end! ! end! ! module Surrounded! module Context! module InstanceMethods! def role?(name, &block)! return false unless role_map.role?(name)! accessor = block.binding.eval('self')! role_map.role_player?(accessor) && ! role_map.assigned_player(name)! end! end! end! end

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module Surrounded! ! def method_missing(meth, *args, &block)! context.role?(meth){} || super! end! ! def respond_to_missing?(meth, include_private=false)! !!context.role?(meth){} || super! end! ! end! ! module Surrounded! module Context! module InstanceMethods! def role?(name, &block)! return false unless role_map.role?(name)! accessor = block.binding.eval('self')! role_map.role_player?(accessor) && ! role_map.assigned_player(name)! end! end! end! end

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module Surrounded! ! def method_missing(meth, *args, &block)! context.role?(meth){} || super! end! ! def respond_to_missing?(meth, include_private=false)! !!context.role?(meth){} || super! end! ! end! ! module Surrounded! module Context! module InstanceMethods! def role?(name, &block)! return false unless role_map.role?(name)! accessor = block.binding.eval('self')! role_map.role_player?(accessor) && ! role_map.assigned_player(name)! end! end! end! end

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module Surrounded! ! def method_missing(meth, *args, &block)! context.role?(meth){} || super! end! ! def respond_to_missing?(meth, include_private=false)! !!context.role?(meth){} || super! end! ! end! ! module Surrounded! module Context! module InstanceMethods! def role?(name, &block)! return false unless role_map.role?(name)! accessor = block.binding.eval('self')! role_map.role_player?(accessor) && ! role_map.assigned_player(name)! end! end! end! end

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Control & 
 Plan Locality

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–Richard Gabriel Piecemeal growth is a reality. What gets in its way and prevents software habitability is overdesign, overabstraction, and the beautiful, taut monument of software.

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– Jim “Cope” Coplien No approach or method can ever be perfect, because its designers cannot control the entire world.

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Thanks! Jim Gay @saturnflyer ! ! ! ! ! clean-ruby.com clean-ruby.com/dsl github.com/saturnflyer/surrounded

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What is missing?

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What is missing? Concurrency Contracts

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–Herb Sutter It is far, far easier to make a correct program fast than it is to make a fast program correct.

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What system is missing?