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Village

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Open landscape

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Street

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City

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City

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Crumbling street

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Building maintenance

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Big or Small? Stand up if in your codebase you… • have more than 50 models • have a class with more than a 1000 LOC • have an ActiveRecord model with more than 30 :has_many • can’t run your full test suite on your machine • can’t run your test suite on your machine in under 20 minutes

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Street

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Structural Engineering in Ruby Stephan Hagemann

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The only thing that ultimately let’s you reign in complexity within one app are components

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As a language, Ruby does not have components

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Gems can act as components

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…they work well

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For Rails, the situation kinda sucks…

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…but works ok

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Let’s make it better!

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Just a normal Rails app
 with some extra structure…

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Structural 
 Costs + Benefits

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Method 2 LOC Costs Hide logic Benefits Allow Reuse

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Class 2 LOC Costs Bundle logic and data Benefits Allow Reuse

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Namespace 2 LOC Costs Prevent naming collisions in the global namespace Benefits Group 
 classes 
 and methods

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Component

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WHAT IS A COMPONENT?

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Labeled Content + Explicit Dependencies

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Labeled, Unique Content + Explicit, Directed, Acyclic Dependencies

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@shageman cbra.info ?

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@shageman cbra.info

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@shageman cbra.info ? ?

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Labeled, Unique Content + Explicit, Directed, Acyclic Dependencies

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@shageman cbra.info

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A depends on B … A B

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thus B can not depend on A A B X

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… and you can’t cheat A B X C

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Structure Benefit Cost Method Allow reuse, 
 hide logic 2 Class Bundle logic and data, allow reuse 2 Namespace Prevent naming collisions, group classes and methods 2

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Gem

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Gem 88 LOC Costs Create provably independent
 package of 
 code Benefits bundle gem awesome_lib Allow 
 Distribution

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Gem + Engine 528 LOC Costs Create provably independent
 package of 
 code with 
 Rails Benefits rails plugin new components/awesome_engine --full --mountable Allow 
 Distribution

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Structure Benefit Cost Method Allow reuse, 
 hide logic 2 Class Bundle logic and data, allow reuse 2 Namespace Prevent naming collisions, group classes and methods 2 Component Allow Distribution, Create provably independent package of code 88 Rails Component Allow Distribution, Create provably independent package of code with Rails 528

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ML predictor X

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1 component with 100 elements 1,267,650,600,228,230,000,000,000,000,000 2 component with 50 elements 2,251,799,813,685,150 4 component with 25 elements 134,217,624 5 component with 20 elements 5,242,775 10 component with 10 elements 10,130 * assuming a lot of stuff, including complexity growing according to Reed’s law

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Structure Benefit Cost Method Allow reuse, 
 hide logic 2 Class Bundle logic and data, allow reuse 2 Namespace Prevent naming collisions, group classes and methods 2 Component Allow Distribution, Create provably independent package of code 88 Rails Component Allow Distribution, Create provably independent package of code with Rails 528

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2 LOC Costs

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Structure Benefit Cost Method Allow reuse, 
 hide logic 2 Class Bundle logic and data, allow reuse 2 Namespace Prevent naming collisions, group classes and methods 2 Component Allow Distribution, Create provably independent package of code 88 Rails Component Allow Distribution, Create provably independent package of code with Rails 528

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Let’s make it better!

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Share the stories of your large app!

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Reduce Rails component costs!

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Improve CI/CD integrations

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Fix cross-component 
 dependency versioning

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Can we create 
 component extractors?

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Street

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Building maintenance

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City

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Futuristic skyscraper