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Wisdom Wednesday - Refactoring
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ruby_refactoring.md

Intros

Code Climate guidelines

  • If PR is urgent, ask a GitHub repo admin to approve in Code Climate, then immediately fix the offenses. Don't open a new ticket.
  • If PR is not urgent, take the time to understand the issue and fix it, unless it's a false positive.
  • Walk through reading up on offense in CC

OO principles

Sandi Metz

  • https://www.sandimetz.com/blog/2009/06/12/ruby-case-statements-and-kind-of
  • It is not the job on any object to tell any other object how to behave.
  • Objects create behavior by passing messages back and forth. They tell each other what, not how.
  • What is the event/notification/request and it is the responsibility of the sender.
  • How is the behavior/implementation and it should be completely hidden in the receiver.
  • Each object knows its own implementation and it exhibits that behavior when it receives a message.
  • No object in your system should have to know the class of any other object in order to know how to behave. Everything is a Duck. Tell the Duck what and the Duck should know how.
  • The last object that could possibly receive the message is the object that should implement the behavior.

Kevin Berridge

  • https://vimeo.com/91672848
  • The only thing an object can do with another object is send it a message
  • The only thing an object can know about another object is what messages it accepts
  • Message describes the what, and hides the how
  • To control complexity, one must embrace simplicity
  • Traffic light example: all it knows about is its current color state and the passage of time. It doesn't know anything about what type of intersection, vehicles, etc.
  • End goal: malleable, extensible, reusable, simple
  • Blind trust: allows objects to collaborate without binding themselves to context and is necessary in any application that expects to grow and change.
  • OO design requires that you shift from thinking of the world as a collection of predefined procedures to modeling the world as a series of messages that pass between objects.

Examples

AppealEvents

Why is code not OO?

  • Adding a new appeal type will require modifying the all method, leading to Divergent Change.
  • The logic and data for combining the events for each appeal type is jammed into one class, resulting in a Large Class
  • AppealEvents should not know how LegacyAppeal implements all
  • Tell, Don't Ask
  • AppealEvent takes in different arguments at different times: hearing, type, disposition

Benefits of refactoring

  • Reveals unused code: AppealEvent#to_hash, calling to_hash in V2::LegacyAppealStatusSerializer#events
  • Code is easier to read
  • Makes testing easier, not clear where everything is tested. For example, supplemental claims tested in spec/feature/api/v2/appeals_spec.rb
  • Reveals missing specs: appeal_events_spec was only testing legacy appeals
  • Reveals code in AppealEvent that only applies to legacy appeals and can be extracted out: disposition=, issue_disposition=
  • date, type Data Clump or Parameter Object

Code smell examples

Special Case Pattern

https://www.rubytapas.com/2013/07/01/episode-112-special-case/

Null Object Pattern

https://thoughtbot.com/upcase/videos/live-coding-session-replace-conditional-with-null-object https://www.sandimetz.com/blog/2014/12/19/suspicions-of-nil

  • Avoid try

Concerns

  • Moving lines from a class into a concern and the including the concern back in the class (shoving under the rug)
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