Refactor: Extract and Isolate

Break down complex code into focused, reusable units.

Extract Method

When to Extract

• Function > 20 lines
• Code block has a distinct purpose
• Same logic repeated
• Deep nesting (> 3 levels)

Extract Class

When to Extract

• Class > 300 lines
• Multiple distinct responsibilities
• Group of related methods/properties
• Feature envy

Extract Protocol/Interface

When to Extract

• Multiple implementations possible
• Testing requires mocking
• Dependency inversion needed

Checklist

1. Identify extraction boundary
2. Choose good name for new unit
3. Move code to new location
4. Update references
5. Add tests for new unit
6. Verify original tests pass