AgentSkillsCN

m09-domain

精通 C++ 领域建模（DDD）。触发点：实体、值对象、聚合根、仓储、Pimpl 模式、类设计、不变量。

SKILL.md
--- frontmatter
name: m09-domain
description: "Mastering C++ Domain Modeling (DDD). Triggers: Entity, Value Object, Aggregate, Repository, Pimpl, Class Design, Invariant."

C++ Domain Modeling

Core Question

Identity or Value?

  • •Value Object: Defined by attributes (Color, Money). Equality via comparison. Copyable.
  • •Entity: Defined by Identity (User, Socket). Equality via ID. Non-copyable (usually).

Error → Design Question

IssueDesign Question
Data InconsistencyAre public fields allowing invalid states?
Object SlicingAre you passing polymorphic Entities by Value?
Header HellAre you leaking implementation details? (Use Pimpl).

Thinking Prompt

  1. •

    Is it copyable?

    • •Yes? → Value Type (Rule of Zero, defaults).
    • •No? → Entity (Delete copy ctor, enable move).
  2. •

    Does it have invariants?

    • •Yes? → class with private data + public methods.
    • •No? → struct (POD).
  3. •

    Does it own others?

    • •Aggregate Root? → Owns children via std::vector / unique_ptr.

Trace Up / Down

  • •Trace Down:
    • •Intent: "User has a Name and an Address."
    • •Code: class User (Entity) holds Name (Value) and Address (Value).

Quick Reference

PatternC++ Implementation
Value Objectstruct + operator<=>.
Entityclass + Deleted Copy + ID field.
RepositoryPure Virtual Interface (virtual ... = 0).
AggregateParent class owning children.