East Oriented Code

Better Message Passing == Better Code

BACKGROUND

Definition

Presentation on Messaging with code samples using East Orientation (& Injection)

• Eastward is sending a message (telling)
• Westward is receiving a message (usually after asking)

CREDIT

• Dr. Alan Kay - Rules to design good messaging; AKA good OOD. Many people cite this source as messaging inspiration:

  • The Meaning of "Object-Oriented Programming" http://userpage.fu-berlin.de/~ram/pub/pub_jf47ht81Ht/doc_kay_oop_en

• James Ladd - Created Eastward Oriented Rules (original blog is unavailable)

  • Blog: "Why we fail at OO": http://jamesladdcode.com/?p=12

• Jim Gay EASTWARD APPLIED to RUBY: (RubyConf 2014) Eastward Ho!

  • Talk: https://www.youtube.com/watch?v=kXcrClJcfm8
  • Blog: https://www.saturnflyer.com/blog/enforcing-encapsulation-with-east-oriented-code & https://www.saturnflyer.com/blog/the-4-rules-of-east-oriented-code-rule-1

Practices

Enforced Tell - Don't Ask

1. Always Return 'self' - especially public methods - (factories & initializers exempt)
2. Objects MAY ONLY QUERY itself - avoid public getters!
3. Objects MAY ONLY CHANGE their own state - avoid public setters!
4. Break the Rules sparingly - mostly for output -- then pass a simple object (ideally immutable) - think Structs & View-Models

Rules 2 & 3 are basically unnecessary if rule 1 is followed closely!

HELPFUL & CONTROVERSIAL

EASY & HELPFUL: with a pipeline architecture:

input -> processing -> output

Examples:

• CLI scripts
• Background Jobs
• Data conversions outputs

Use Case - A Data Exchange

CONTROVERSIAL to use with a "controller" architecture - that expects to "control" - the opposite of East Oriented code.

• Jim Weirich - Decoupling from Rails & his sample code (summarized by DHH)
• DHH - Calls this Test Driven Damage
• Uncle Bob Support for Decoupling & Architecture the Lost Years

Informal Practice

When Strict East isn't practical

Helpful for daily coding - when East Oriented not practical

• Tell, don't ask - Could I return self?, What else canI make private?
• Exceptions common - pass a data for output & formatting - using view-models, value-objects, struct or minimally a hash

I like to explore the practice of getting as close as possible to East Oriented (along with Sandi Metz's Code Complexity Rules & Behavior Injection)

CODE

I don't have access to the Data Exchange I wrote for my previous employer - but Jim Gay's address code can use a similar pipeline flow

• 01_east_west_address.rb - is east-west, very simple and clear -- great when very simple and flexibility isn't needed
• 02_east_address.rb - is east only is great when additional for flexible outputs and keeping processing clear (only objects can change and query themselves)

Given Time and Interest

• 03_east_injection_address.rb - injection and decorators allow lots of flexibility and complexity while preserving the benefits of East Orientated Message passing with one place data is mutated and single purpose for each class.
• 00_jim_gay_refactor_process.md - Jim Gay's refactoring process from East/West to West