nw-progressive-refactoring

Progressive Refactoring (Refactoring Priority Premise)

Based on the Refactoring Priority Premise (RPP) from the Alcor Academy curriculum.

RPP Levels (L1-L6)

Execute levels in mandatory sequence. Lower levels before higher.

Level 1: Foundation (Readability)

Focus: eliminate clutter, improve naming, remove dead code.

Smells: Dead Code | Comments (how-comments) | Speculative Generality | Lazy Class.

Transformations: Rename | Extract (variables/constants) | Safe Delete.

Impact: 80% of readability improvement value.

Test smells: Obscure Test | Hard-Coded Test Data | Assertion Roulette.

Level 2: Complexity Reduction (Simplification)

Focus: method extraction, duplication elimination.

Smells: Long Method | Duplicate Code | Complex Conditionals.

Transformations: Extract (methods) | Move (common code).

Impact: 20% additional readability improvement.

Test smells: Eager Test | Test Code Duplication | Conditional Test Logic.

Level 3: Responsibility Organization

Focus: class responsibilities, coupling reduction.

Smells: Large Class | Feature Envy | Inappropriate Intimacy | Data Class | Divergent Change | Shotgun Surgery.

Transformations: Move | Extract (classes).

Test smells: Test Class Bloat | Mystery Guest | General Fixture.

Level 4: Abstraction Refinement

Focus: parameter objects, value objects, abstractions.

Smells: Long Parameter List | Data Clumps | Primitive Obsession | Middle Man.

Transformations: Extract (objects) | Inline | Move.

Level 5: Design Pattern Application

Focus: Strategy | State | Command patterns.

Smells: Switch Statements | complex state-dependent behavior.

Transformations: Extract (interfaces) | Move (to polymorphic structure).

Level 6: SOLID++ Principles

Focus: SOLID principles, architectural patterns.

Smells: Refused Bequest | Parallel Inheritance Hierarchies.

Transformations: Extract (interfaces) | Move (responsibilities) | Safe Delete (violations).

RPP Cascade Rule

MANDATORY: complete each level fully before moving to the next. Do not skip levels.

80% of refactoring value comes from readability improvements (L1-L2).

Focus effort on L1-L2 for maximum impact. Move to higher levels only when needed.

Fast-Path for Small Changes

When GREEN phase produced < 30 LOC of new production code:

• Quick scan for obvious naming/duplication issues (2-3 min max)
• Mark COMPLETED with note "fast-path: <30 LOC"

L4-L6 Timing

L4-L6 architecture refactoring runs at orchestrator Phase 2.25 (once after all steps complete), not during each TDD inner loop.

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22 Code Smell Taxonomy

Bloaters

| Smell | Detection | Treatment | Level |

|-------|-----------|-----------|-------|

| Long Method | >20 lines, multiple responsibilities | Extract Method, Compose Method | L2 |

| Large Class | >300 lines, too many fields | Extract Class, Extract Subclass | L3 |

| Primitive Obsession | Raw strings for domain concepts, magic numbers | Replace Data Value with Object | L4 |

| Long Parameter List | >=4 parameters | Introduce Parameter Object | L4 |

| Data Clumps | Same parameter groups repeated | Extract Class, Introduce Parameter Object | L4 |

Object-Orientation Abusers

| Smell | Detection | Treatment | Level |

|-------|-----------|-----------|-------|

| Switch Statements | Switch on type, complex if-else chains | Replace with Polymorphism, Strategy | L5 |

| Temporary Field | Fields empty most of the time | Extract Class, Null Object | L3 |

| Refused Bequest | Subclass doesn't support parent interface | Push Down, Replace Inheritance with Delegation | L6 |

| Alternative Classes, Different Interfaces | Same function, different names | Rename Method, Extract Superclass | L3 |

Change Preventers

| Smell | Detection | Treatment | Level |

|-------|-----------|-----------|-------|

| Divergent Change | One class changed for different reasons | Extract Class | L3 |

| Shotgun Surgery | Change requires many small changes to many classes | Move Method, Move Field, Inline Class | L3 |

| Parallel Inheritance Hierarchies | Creating subclass requires another subclass | Move Method, Move Field | L6 |

Dispensables

| Smell | Detection | Treatment | Level |

|-------|-----------|-----------|-------|

| Comments (how-comments) | Comments explaining complex code | Extract Method, Rename Method | L1 |

| Duplicate Code | Same code structure in multiple places | Extract Method, Pull Up Method | L2 |

| Lazy Class | Class with few methods, little functionality | Inline Class, Collapse Hierarchy | L1 |

| Data Class | Only fields and getters/setters | Move Method, Encapsulate Field | L3 |

| Dead Code | Unused variables, methods, classes | Delete unused code | L1 |

| Speculative Generality | Abstractions for future features | Collapse Hierarchy, Inline Class | L1 |

Couplers

| Smell | Detection | Treatment | Level |

|-------|-----------|-----------|-------|

| Feature Envy | Method uses another object's data more than its own | Move Method, Extract Method | L3 |

| Inappropriate Intimacy | Classes know too much about each other | Move Method, Extract Class, Hide Delegate | L3 |

| Message Chains | a.getB().getC().getD() | Hide Delegate, Extract Method | L3 |

| Middle Man | Class only delegates to another | Remove Middle Man, Inline Method | L4 |

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5 Atomic Transformations

Rename

Change name without changing behavior. Applies to: variables | methods | classes | fields | parameters.

Safety: use IDE refactoring tools, verify all references updated, run tests, commit.

Extract

Take portion of code, create new element. Applies to: methods | classes | variables | constants | interfaces.

Safety: identify code, create element with intention-revealing name, move code, replace original with call, test, commit.

Inline

Replace code element with its implementation. Applies to: methods | variables | classes.

Safety: verify no side effects, replace all calls, remove original, test, commit.

Move

Relocate code element to different scope or class. Applies to: methods | fields | classes.

Safety: check dependencies, create in target, update references, remove from source, test, commit.

Safe Delete

Remove unused code elements. Applies to: methods | fields | classes | parameters | variables.

Safety: verify truly unused, check for dynamic references, remove, compile and test, commit.

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For test code smells (9 smells with detection patterns and before/after examples), load the test-refactoring-catalog skill.

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Refactoring Techniques Catalog (Fowler)

Composing Methods

• Extract Function: workhorse refactoring. If you need a comment to explain a block, extract to method with that explanation as name.
• Compose Method (Kerievsky): transform method into composition at same abstraction level. Repeated Extract Function until body reads like pseudocode.
• Inline Function: remove unnecessary abstraction when body is as clear as name. Use in "inline then re-extract" dance.
• Replace Temp with Query: replace temporary variable with method call.

Moving Features

• Move Function: relocate to more appropriate class/module. Addresses Feature Envy.
• Move Field: move field to class that uses it most.
• Extract Class: decompose Large Class by moving related data+methods to new class.

Organizing Data

• Replace Data Value with Object: turn simple data value into full object. Addresses Primitive Obsession.
• Introduce Parameter Object: group parameters that go together. Addresses Long Parameter List.
• Encapsulate Variable/Collection: protect data from direct access. Return unmodifiable view.

Simplifying Conditionals

• Decompose Conditional: extract condition + branches to named functions showing intent.
• Guard Clauses: handle exceptional cases early, return, leave main logic unnested.
• Replace Conditional with Polymorphism: replace type-based conditionals with class hierarchy.

Refactoring to Patterns (Kerievsky)

Don't design patterns upfront - refactor toward them as needs emerge:

• Extract Method repeatedly -> Compose Method -> Template Method
• Encapsulate Field + Move Method -> Strategy
• Extract Class + Move Method -> Decorator

Key Principles

• Behavior-preserving: if behavior changes, it's not refactoring
• Automated refactoring (IDE) preferred over manual
• Cohesion and clarity over line-count thresholds
• Function size: Single Responsibility + Consistent Abstraction + Self-Documenting names

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For complex architectural refactoring, load the mikado-method skill.