Skill: Casts

"Casts change storage format. Accessors change presentation."

The Decision

Use Cast when:

• Value requires different storage format (int → Money)
• Transformation applies on both read AND write
• Value Object should be reusable across models

Use Accessor when:

• Computed from other attributes
• Read-only transformation
• Depends on model state/context

The Heuristic

Ask: "Does this transform how data is stored, or how it's displayed?"

• Storage → Cast
• Display → Accessor

The Quick Test

Ask Yourself	Answer	Use
Reusable across models?	Yes	Cast
Needs read + write?	Yes	Cast
Depends on other attributes?	Yes	Accessor
Computed value?	Yes	Accessor

Real-World Examples

For concrete examples, see examples.md.