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

• Identify extraction boundary

• Choose good name for new unit

• Move code to new location

• Update references

• Add tests for new unit

• Verify original tests pass