M09 Domain

What it does

The M09 Domain skill assists in structuring data and designing software based on Domain-Driven Design (DDD) principles, specifically within a Rust programming context. It helps define domain concepts by determining whether they should be modeled as Entities (with unique identities), Value Objects (interchangeable values), or Aggregates (groups of related objects). The skill provides guidance on invariants, ownership implications, and mapping these concepts to appropriate Rust patterns and code structures.

When to use it

• When designing a new software system based on Domain-Driven Design principles.
• To determine whether a specific data concept should be modeled as an Entity or Value Object.
• For establishing aggregate boundaries within a domain model.
• To define validation rules and invariants for domain objects.
• When needing to translate domain concepts into Rust code patterns (structs, traits, enums).

Key capabilities

• Entity vs. Value Object Identification: Determines if a concept requires a unique identity or can be treated as an interchangeable value.
• Aggregate Boundary Definition: Helps identify groups of objects that must maintain consistency together.
• Invariant Specification: Guides the definition of rules and constraints that domain objects must adhere to.
• Rust Pattern Mapping: Provides guidance on translating DDD concepts into corresponding Rust code patterns (e.g., structs, traits, enums).
• Ownership Guidance: Offers advice on ownership implications for different modeling choices (owned, shared, weak references).

Example prompts

• "Should 'Customer' be modeled as an Entity or a Value Object?"
• "What are the invariants that must hold for a 'Transaction'?"
• "How do I model this concept in Rust using DDD principles?"
• “What is the best way to define ownership for these related objects?”

Tips & gotchas

• This skill focuses on design choices within a Domain-Driven Design context, specifically when implementing in Rust. It does not provide implementation details beyond pattern suggestions.
• Understanding basic DDD concepts (Entities, Value Objects, Aggregates) is helpful to effectively utilize this skill.