Type System Patterns for Code Review

Overview

A strong type system is the first line of defense against bugs. When used well, types make illegal states unrepresentable — the compiler catches entire classes of errors before any test runs.

When to Use

• APIs accepting raw strings where a typed value is expected
• Functions returning null/undefined or throwing where a Result type belongs
• Codebases with frequent any casts or type assertions
• State machines implemented as ad-hoc string/boolean flags
• Runtime validation that could be moved to compile time

Quick Reference