Refactoring: Refactorings/Remove Assignments to Parameters

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When in the method body, the code modifies the parameter variables passed into it to become another object:

Suppose foo is a parameter passed into a method. Somewhere in the code we say foo = another_object

Mechanics

  1. Create a temporary variable for the parameter
  2. Replace all parameter references after the assignment to the temporary variable
  3. Change assignment to assign to temporary variable
  4. Test

Example

Before

def discount(input_val, quantity, year_to_date)
  input_val -= 2 if input_val > 50
  input_val -= 1 if quantity > 100
  input_val -= 4 if year_to_date > 10000
  input_val

After

def discount(input_val, quantity, year_to_date)
  result = input_val
  result -= 2 if input_val > 50
  result -= 1 if quantity > 100
  result -= 4 if year_to_date > 10000
  result
Note: Ruby always passes parameters by value, so internal modification within method is not reflected in outer scope
Refactorings
Composing Methods

Extract Method • Inline Method • Inline Temp • Replace Temp with Query • Replace Temp with Chain • Introduce Explaining Variable • Split Temporary Variable • Remove Assignments to Parameters • Replace Method with Method Object • Substitute Algorithm • Replace Loop with Collection Closure Method • Extract Surrounding Method • Introduce Class Annotation • Introduce Named Parameter • Remove Named Parameter • Remove Unused Default Parameter • Dynamic Method Definition • Replace Dynamic Receptor with Dynamic Method Definition • Isolate Dynamic Receptor • Move Eval from Runtime to Parse Time

Moving Features Between Objects

Move Method • Move Field • Extract Class • Inline Class • Hide Delegate • Remove Middle Man

Organizing Data

Self Encapsulate Field • Replace Data Value with Object • Change Value to Reference • Change Reference to Value • Replace Array with Object • Replace Hash with Object • Change Unidirectional Association to Bidirectional • Change Bidirectional Association to Unidirectional • Replace Magic Number with Symbolic Content • Encapsulate Collection • Replace Record with Data Class • Replace Type Code with Polymorphism • Replace Type Code with Module Extension • Replace Type Code with State-Strategy • Replace Subclass with Fields • Lazily Initialized Atribute • Eagerly Initialized Attribute

Simplifying Conditional Expressions

Decompose Conditional • Recompose 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 • Replace Error Code with Exception • Replace Exception with Test • Introduce Gateway • Introduce Expression Builder

Dealing with Generalization

Pull Up Method • Push Down Method • Extract Module • Inline Module • Extract Subclass • Introduce Inheritance • Collapse Hierarchy • Form Template Method • Replace Inheritance with Delegation • Replace Delegation with Hierarchy • Replace Abstract Superclass with Module

Big Refactorings

Tease Apart Inheritance • Convert Procedural Design to Objects • Separate Domain from Presentation • Extract Hierarchy

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