Design Before Implementing

Skill: Design Before Implementing

Purpose

Make explicit design decisions before writing implementation code.

When to Apply

• Adding a new module or class
• Introducing a new dependency
• Changing how two components interact
• Feature that touches 3+ existing modules

Design Checklist

1. Define the interface first

   • What are the inputs and outputs?
   • What does the caller need to know vs. what's internal?
   • Write the function/class signature before the body

2. Identify dependencies

   • What does this component need from the outside?
   • Depend on protocols/interfaces, not concrete implementations
   • If a new external dependency is needed, flag it