2nd/10_Wiki/Topics/Domain_Programming/Architecture/Implementation Separation.md

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id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-implementation-separation	Implementation Separation	10_Wiki/Topics	verified	self	Implementation Separation Interface-Implementation Split Hexagonal Boundaries	none	A	0.9	applied	architecture interface dependency-inversion hexagonal ports-adapters		2026-05-10	pending	language framework TypeScript/Python/Go language-agnostic

Implementation Separation

매 한 줄

"매 'what' 매 'how' 의 분리". Implementation separation 매 interface (contract) 매 implementation (mechanism) 매 명시적 분리 — 매 dependency inversion, ports-and-adapters, hexagonal architecture 의 core idea. 매 testability, swappability, evolution 매 enable.

매 핵심

매 Why separate

• Test: 매 fake/mock 매 swap-in.
• Swap: 매 Postgres → DynamoDB 매 caller code unchanged.
• Boundary: 매 layer/module 매 명확.
• Parallel work: 매 interface freeze → 매 team 매 parallel implementation.

매 Levels of separation

1. Interface keyword (Java, C#, Go, TypeScript): 매 syntax 매 enforce.
2. Abstract base class (Python, C++): 매 ABC, virtual.
3. Protocol/structural typing (Python typing.Protocol, TypeScript): 매 duck typing 매 static check.
4. Trait (Rust): 매 zero-cost.
5. Module boundary (Haskell .hs-boot, OCaml .mli): 매 module-level.

매 응용

1. Repository pattern: 매 UserRepo interface, 매 PgUserRepo impl.
2. Strategy pattern: 매 algorithm 매 swap.
3. Adapter (port): 매 external service 매 wrap.
4. Test doubles: 매 InMemory* impl.

💻 패턴

TypeScript — port + adapter

// Port (domain owns this)
export interface UserRepo {
  findById(id: string): Promise<User | null>;
  save(u: User): Promise<void>;
}

// Adapter (infrastructure)
export class PgUserRepo implements UserRepo {
  constructor(private db: Pool) {}
  async findById(id: string) {
    const r = await this.db.query('select * from users where id=$1', [id]);
    return r.rows[0] ? mapUser(r.rows[0]) : null;
  }
  async save(u: User) {
    await this.db.query('insert into users ...', [u.id, u.name]);
  }
}

// In-memory test double
export class InMemoryUserRepo implements UserRepo {
  private map = new Map<string, User>();
  async findById(id: string) { return this.map.get(id) ?? null; }
  async save(u: User)         { this.map.set(u.id, u); }
}

Python Protocol (structural)

from typing import Protocol

class Notifier(Protocol):
    def send(self, to: str, msg: str) -> None: ...

class EmailNotifier:
    def send(self, to: str, msg: str) -> None:
        smtp.sendmail(...)

class SlackNotifier:
    def send(self, to: str, msg: str) -> None:
        requests.post("https://slack/api", json={"channel": to, "text": msg})

def notify_user(n: Notifier, user_id: str, msg: str) -> None:
    n.send(user_id, msg)  # any structural match works

Go — implicit interface

type Cache interface {
    Get(key string) ([]byte, bool)
    Set(key string, val []byte, ttl time.Duration)
}

type RedisCache struct{ client *redis.Client }
func (r *RedisCache) Get(k string) ([]byte, bool) { /* ... */ }
func (r *RedisCache) Set(k string, v []byte, ttl time.Duration) { /* ... */ }

type MemCache struct{ m sync.Map }
func (m *MemCache) Get(k string) ([]byte, bool) { /* ... */ }
func (m *MemCache) Set(k string, v []byte, ttl time.Duration) { /* ... */ }

Rust trait

pub trait Storage {
    fn put(&self, key: &str, val: &[u8]) -> anyhow::Result<()>;
    fn get(&self, key: &str) -> anyhow::Result<Option<Vec<u8>>>;
}

pub struct S3Storage { client: aws_sdk_s3::Client }
impl Storage for S3Storage { /* ... */ }

pub struct LocalFs { root: PathBuf }
impl Storage for LocalFs { /* ... */ }

pub fn save_blob<S: Storage>(s: &S, k: &str, v: &[u8]) -> anyhow::Result<()> {
    s.put(k, v)
}

Hexagonal layout

src/
  domain/        # pure logic, no I/O
    user.ts
    order.ts
  ports/         # interfaces
    user_repo.ts
    payment_gateway.ts
  app/           # use-cases, depend on ports only
    place_order.ts
  adapters/      # impl of ports
    pg_user_repo.ts
    stripe_gateway.ts
  infra/         # composition root
    main.ts

매 결정 기준

상황	Approach
매 single impl, no test isolation needed	매 직접 class — 매 over-engineer 금지
매 ≥2 impls or test doubles 필요	매 interface/protocol/trait
매 cross-team boundary	매 interface freeze 매 contract
매 swappable infra (DB, queue, cache)	매 port + adapter
매 perf-critical hot loop	매 generics/static dispatch (no vtable)

기본값: 매 ports 매 domain 옆, adapters 매 infra layer, 매 composition root 매 wire.

🔗 Graph

• 부모: Hexagonal Architecture · Dependency Inversion Principle
• 변형: Ports and Adapters · Clean-Architecture · Onion-Architecture
• 응용: Test-Doubles
• Adjacent: High-Cohesion-Low-Coupling · SOLID

🤖 LLM 활용

언제: 매 architecture refactor; 매 testability 부족; 매 multiple infra backend; 매 team boundary. 언제 X: 매 single-use script; 매 prototype; 매 only one impl forever.

❌ 안티패턴

• IFoo + FooImpl 매 1:1 forever: 매 interface 매 swap/test point 없으면 매 잡음.
• Leaky abstraction: 매 interface method 매 SQL string 받음 — 매 impl 의 detail 노출.
• Anemic port: 매 CRUD method 만 매 interface — 매 domain logic 매 caller 에 leak.
• Adapter 매 domain 의 의존: 매 dep 매 wrong direction.

🧪 검증 / 중복

• Verified (Cockburn 2005 "Hexagonal Architecture", Evans DDD, Martin "Clean Architecture", Vernon IDDD).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — full content (port/adapter, multi-language patterns)