m09-domain

Domain-driven design patterns for modeling entities, value objects, and aggregates in Rust. Layer 2: Design Choices What is this concept's role in the domain? Before modeling in code, understand: Before creating a domain type: What's the concept's identity? What invariants must hold? Who owns this data? To domain constraints (Layer 3): To implementation (Layer 1): - Distinguishes between Entities (unique identity required), Value Objects (interchangeable by value), and Aggregates (owned hierarchies), with clear Rust patterns for each - Emphasizes invariant preservation through private fields, validated constructors, and type-state patterns - Provides templates for common DDD structures: newtypes for value objects, structs with ID fields for entities, and module boundaries for aggregates - Traces design decisions upward to domain constraints and downward to ownership and type-driven implementation patterns - Is it an Entity (identity matters) or Value Object (interchangeable)? - What invariants must be maintained? - Where are the aggregate boundaries?