Long method

  • flog

Extract Method

Replace Temp with Query

Large Class

difficult to understand and harder to change or reuse => more bugs and conflicts

Symptoms

  • Can’t describe what the class does in one sentence
  • Can’t tell what class does without scrolling
  • Class needs to change for more than one reason
  • more than 7 methods
  • total flog score of 50

Solutions

  • Move method
  • Extract Class
  • Replace Conditional with Polymorphism
  • Extract Value Object
  • Extract Decorator
  • Replace Subclasses with Strategies

Prevention

  • Single Responsibility Principle
  • Composition Over Inheritance
  • Dependency Inversion Principle
  • Open/Closed Principle

Private Method

  • Private methods can’t be reused between classes => duplicated => extract private methods to new classes
  • Private methods can’t be tested directly
  • Private methods are often the easiest to extract to new classes
  • Keeping a class’s private interface as small as possible is a best practice as well.

God Class

God class is class that seems to know everything about an application

User class is a sample

Feature Envy

Feature envy reveals a method that would work better on a different class

Symptoms

  • Repeated references to the same object
  • Parameters or local variables which are used more than methods and instance variables of the class in question
  • Method that includes a class name in their own names (invite_user)
  • Private methods on the same class that accept the same parameter
  • Law of Demeter
  • Tell, Don't Ask

Solutions

  • Extract method
  • Move method
  • In-line class

Prevention

  • Tell, don't ask
  • Law of Demeter

Case Statement

Sign that a method contains too much knowledge

Symptoms

  • Check the class of the class of an object
  • check a type code
  • adding when clauses

Solutions

  • Replace Type Code with Subclasses
  • Replace Conditional with Polymorphism
  • Use Convention over Configuration

Long Parameter List

Solutions

  • Introduce Parameter Object
  • Extract Class

Anti-Solution

  • Use hash of named parameters

Duplicated Code

  • Don’t repeat yourself

Symptoms

  • Copy and pasting
  • Shotgun Surgery

Solutions

  • Extract Method
  • Extract Class
  • Extract Partial
  • Replace Conditional with Polymorphism

  • Replace Conditional with Null Object

    Remove duplicated checks for nil values

Prevention

  • Follow Single Responsibility Principle

Uncommunicative Name

Symptoms

  • Difficult understanding a method or class
  • Methods or classes with similar names but dissimilar functionality
  • Redundant names, such as names which include type of object to which they refer.

Solutions

  • Rename method
  • Extract class
  • Extract method
  • In-line class

STI

Symptoms

  • You need to change from one subclass to another
  • Behavior is shared among some subclass but not others.
  • One subclass is a fusion of one or more other subclasses.

Solutions

  • If you’re using STI to reuse common behavior, use Replace Subclasses with Strategies to switch to a composition-based model.
  • If you’re using STI so that you can easily refer to several different classes in the same table, switch to using a polymorphic association instead.

Prevention

  • Composition over Inheritance

Comments

Mixin

Callback