refactoring-cheatsheet.md

Refactorings List

The below will be my notes on each of the sections in Refactoring Improving the Design of Existing Code

• Composing Methods
  • Extract Method
  • Inline Method
  • Inline Temp
  • Replace Temp with Query
  • Introduce Explaining Variable
  • Split Temporary Variable
  • Remove Assignments to Parameters
  • Replace Method with Method Object
  • Substitute Algorithm
• Moving Features Between Objects
  • Move Method
  • Move Field
  • Extract Class
  • Inline Class
  • Hide Delegate
  • Remove Middle Man
  • Introduce Foreign Method
  • Introduce Local Extension
• Organizing Data
  • Self Encapsulate Field
  • Replace Data Value with Object
  • Change Value to Reference
  • Change Reference to Value
  • Replace Array with Object
  • Duplicate Observed Data
  • Change Unidirectional Association to Bidirectional
  • Change Bidirectional Association to Unidirectional
  • Replace Magic Number with Symbolic Constant
  • Encapsulate Field
  • Encapsulate Collection
  • Replace Record with Data Class
  • Replace Type Code with Class
  • Replace Type Code with Subclasses
  • Replace Type Code with State/Strategy
  • Replace Subclass with Fields
• Simplifying Conditional Expressions
  • Decompose Conditional
  • Consolidate Conditional Expression
  • Consolidate Duplicate Conditional Fragments
  • Remove Control Flag
  • Replace Nested Conditional with Guard Clauses
  • Replace Conditional with Polymorphism
  • Introduce Null Object
  • Introduce Assertion
• Making Method Calls Simpler
  • Rename Method
  • Add Parameter
  • Remove Parameter
  • Separate Query from Modifier
  • Parameterize Method
  • Replace Parameter with Explicit Methods
  • Preserve Whole Object
  • Replace Parameter with Method
  • Introduce Parameter Object
  • Remove Setting Method
  • Hide Method
  • Replace Constructor with Factory Method
  • Encapsulate Downcast
  • Replace Error Code with Exception
  • Replace Exception with Test
• Dealing with Generalization
  • Pull Up Field
  • Pull Up Method
  • Pull Up Constructor Body
  • Push Down Method
  • Push Down Field
  • Extract Subclass
  • Extract Superclass
  • Extract Interface
  • Collapse Hierarchy
  • Form Template Method
  • Replace Inheritance with Delegation
  • Replace Delegation with Inheritance
• Big Refactorings
  • Tease Apart Inheritance
  • Convert Procedural Design to Objects
  • Separate Domain from Presentation
  • Extract Hierarchy

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Composing Methods

Extract Method

https://refactoring.com/catalog/extractMethod.html

• Helps provide clarity of purpose for the enclosed statements
• Removes the need for comments when using expressive method names
• Consider using even over short pieces of code that are semantically dense
• Consider using if inside the method the statements deal with different layers of abstraction
• Don't use if the extracted piece of code cannot be given a better name than the current method's

Inline Method

https://refactoring.com/catalog/inlineMethod.html

• Helps with needless indirection
• Consider using as an intermediate step to cleaning up badly factored, smaller methods
• Don't use if a subclass overrides the method

Inline Temp

https://refactoring.com/catalog/inlineTemp.html

• Only use when assigning the value of a method call
• Consider using as an intermediate step when refactoring to a Replace Temp with Query

Replace Temp with Query

https://refactoring.com/catalog/replaceTempWithQuery.html

• Helps reduce method size by extracting a commonly used query
• Consider using if a given expression is used only once within the method
• Consider using if the temp variable is only assigned to once within the method

Introduce Explaining Variable

https://refactoring.com/catalog/extractVariable.html

• Helps with expressiveness of conditional statements
• Consider using if many conditionals are being considered
• Consider using Extract Method for the conditional statement if it is a recurring check instead
• Often leads to Replace Temp With Query

Split Temporary Variable

https://refactoring.com/catalog/splitTemporaryVariable.html

• Consider using if you are re-using a temp variable
• Helps refactor code to follow Single Responsibility Principle
• Can likely be identified if the name of the variable does not express what it's used for in a meaningful way (temp, foo, etc.)

Remove Assignments to Parameters

https://refactoring.com/catalog/removeAssignmentsToParameters.html

• Avoid assigning value to parameters, instead use a temp variable
• Helps avoid clarity issues between pass by reference and pass by value
• Output parameters are an exception but should be used in very limited circumstances

Replace Method with Method Object

https://refactoring.com/catalog/replaceMethodWithMethodObject.html

• Introduces the Command Pattern
• Reduces duplication in common work by encapsulating that functionality in an object

Substitute Algorithm

https://refactoring.com/catalog/substituteAlgorithm.html

• Given two algorithms, select the one that is either
  • More performant
  • More succinct
  • More expressive
• Have tests that assert the result of the original algorithm and run them after replacing to insure the new algorithm is a proper substitute

Moving Features Between Objects

Move Method

https://refactoring.com/catalog/moveMethod.html