kotlin

name	kotlin
description	Project-agnostic Kotlin domain modelling skill: rich types, boundary validation, sealed errors, and clean separation of concerns.

Kotlin Domain Modelling Skill

Use this skill whenever you design or refactor domain code, API contracts, validation, typed errors, or mapping between transport/domain/persistence.

Quick reference

• Model business concepts with types, not primitives.
• Validate external input at the boundary before it enters domain.
• Enforce invariants in value objects/entities.
• Represent expected failures with sealed result/error types.
• Keep transport, domain, and persistence models separate.
• Map explicitly at boundaries; avoid leaking framework/DB concerns into domain.

Workflow

1. Identify what layer is being changed (boundary, application, domain, infrastructure).
2. Read only the relevant reference doc(s) below.
3. Apply the minimal correct modelling change.
4. Ensure failures are typed and mappings are explicit.

References

Topic	Reference
Domain types (value class, data class/object, sealed state)	references/domain-types-and-state.md
Separation of concerns and layer responsibilities	references/separation-of-concerns.md
Boundary validation and typed error modelling