The Missing System

Managing coupling and cohesion in our programs is a difficult and never-ending task. Often we struggle to know exactly where to put what code. Over the last few years working with and studying Ruby and DCI I've built up a toolset for managing cohesive set of behaviors for inter-related objects called Surrounded. It helps me maintain related code in the same place and gives me a discussion point for team members implementing features in our systems. We'll walk through the adaptable interface it provides and how it can help your better organize your feature set.

1. The Missing System Or Preparing for Piecemeal Growth
2. Jim Gay @saturnflyer ! clean-ruby.com clean-ruby.com/dsl
3. Jim Gay @saturnflyer ! github.com/saturnflyer/surrounded
7. Habitability & Barriers
8. Patterns of Software
9. –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.
10. –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.
11. 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!
12. ! ! ! ! ! ! ! ! ! ! ! ! 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
13. ! ! ! ! ! ! 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
14. 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
15. person.display_address(template)! ! address.display(template)! ! template.display(address)! ! STDOUT.puts “…”! Tell Don’t Ask
16. –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.
17. –Richard Gabriel ! ! 
 Bugs tell us that we are not capable of producing a master plan.
18. –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.
19. github.com/saturnflyer/surrounded
20. Goals • Preserve existing object behavior / allow extension • Localize use case behavior • Apply behavior only when necessary
21. Goals • Preserve existing object behavior / allow extension • Localize use case behavior • Apply behavior only when necessary
22. class UserActivation! def initialize(admin, user)! @admin = admin! @user = user! end! attr_reader :admin, :user! private :admin, :user! end
23. class UserActivation! def initialize(admin, user)! @admin = admin.extend(Admin)! @user = user! end! attr_reader :admin, :user! private :admin, :user! ! module Admin! #…! end! end
24. 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
25. 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
26. 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
27. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! module Admin! #…! end! end
28. 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
29. 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
30. 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
31. 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
32. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! module Admin! #…! end! end
33. 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
34. 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
35. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! def initialize(admin, user)! super! special_processing(…)! end! ! ! module Admin! #…! end! end
36. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! def initialize(admin, user)! super! special_processing(…)! end! ! ! module Admin! #…! end! end
37. 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
38. 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
39. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! module Admin! #…! end! end
40. Goals • Preserve existing object behavior / allow extension • Localize use case behavior • Apply behavior only when necessary
41. Coupling & Cohesion
42. –Richard Gabriel The primary feature for easy maintenance is locality !
43. –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.
49. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! module Admin! #…! end! end
50. 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
51. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! role :admin do! #…! end! end
52. 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
53. 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
54. 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
55. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! ! ! ! ! ! ! role :admin do! #…! end! end
56. 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
58. Goals • Preserve existing object behavior / allow extension • Localize use case behavior • Apply behavior only when necessary
59. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! def do_something! # use objects and role behaviors! end! ! ! ! ! ! role :admin do! #…! end! end
60. 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
61. class UserActivation! extend Surrounded::Context! ! initialize :admin, :user! ! trigger :do_something do! # use objects and role behaviors! end! ! ! ! ! ! role :admin do! #…! end! end
62. 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]
63. 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, …]
65. 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
66. 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
67. 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
68. 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
69. 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
70. 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
71. 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
72. 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
73. 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
74. Control & 
 Plan Locality
75. –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.
76. – Jim “Cope” Coplien No approach or method can ever be perfect, because its designers cannot control the entire world.
77. Thanks! Jim Gay @saturnflyer ! ! ! ! ! clean-ruby.com clean-ruby.com/dsl github.com/saturnflyer/surrounded
78. What is missing?
79. What is missing? Concurrency Contracts
80. –Herb Sutter It is far, far easier to make a correct program fast than it is to make a fast program correct.
81. What system is missing?