2nd/10_Wiki/Topics/Architecture/Generics-and-Polymorphism.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-generics-and-polymorphism	Generics and Polymorphism	10_Wiki/Topics	verified	self	Parametric Polymorphism 제네릭	none	A	0.9	applied	type-system generics polymorphism		2026-05-10	pending	language framework typescript type-system

Generics and Polymorphism

매 한 줄

"매 한 번 작성, 매 여러 type 에 작동". 매 parametric polymorphism (generics) + ad-hoc polymorphism (overloading / traits) + subtype polymorphism (inheritance) 의 셋이 modern type system 의 backbone. 2026 시점 TS 5.x conditional types, Rust trait + GAT, Go 1.21+ generics 가 매 mainstream.

매 핵심

매 polymorphism 의 종류

• Parametric: type parameter <T> — 매 List, Vec, []T.
• Ad-hoc: overloading, type classes, traits, interfaces with default impl.
• Subtype: 매 Liskov — Cat extends Animal.
• Row / Structural: TS object shape, OCaml row polymorphism.

매 dispatch

• Static (monomorphization): Rust, C++ template — 매 compile-time 에 specialize → zero overhead.
• Dynamic (vtable): Java interface, Go interface, Rust dyn Trait — 매 runtime indirection.

매 응용

1. Collection / container 의 reuse.
2. Algorithm 의 generic write (sort, map).
3. API design 의 type-safe abstraction.
4. Dependency injection 의 decoupling.

💻 패턴

TypeScript — generic constraint

function pluck<T, K extends keyof T>(items: T[], key: K): T[K][] {
  return items.map(i => i[key]);
}
const names = pluck([{ id: 1, name: "Ada" }], "name"); // string[]

TS — conditional + infer

type ReturnT<F> = F extends (...a: any[]) => infer R ? R : never;
type X = ReturnT<() => Promise<number>>; // Promise<number>

Rust — trait + generic

trait Summable: Copy + std::ops::Add<Output = Self> + Default {}
impl<T: Copy + std::ops::Add<Output = T> + Default> Summable for T {}

fn sum<T: Summable>(xs: &[T]) -> T {
    xs.iter().copied().fold(T::default(), |a, b| a + b)
}

Rust — GAT (Generic Associated Type)

trait LendingIterator {
    type Item<'a> where Self: 'a;
    fn next<'a>(&'a mut self) -> Option<Self::Item<'a>>;
}

Rust — dyn vs impl Trait

fn make_static() -> impl Iterator<Item = i32> { (0..10).filter(|x| x % 2 == 0) } // monomorphized
fn make_dyn() -> Box<dyn Iterator<Item = i32>> { Box::new(0..10) }                // vtable

Go — generics (1.21+)

type Number interface { ~int | ~int64 | ~float64 }

func Sum[T Number](xs []T) T {
    var total T
    for _, x := range xs { total += x }
    return total
}

Java — bounded wildcard (PECS)

// Producer Extends, Consumer Super
static double sum(List<? extends Number> xs) {
    double s = 0; for (Number n : xs) s += n.doubleValue(); return s;
}
static void fillWithOnes(List<? super Integer> xs) { xs.add(1); }

Haskell — type class (ad-hoc)

class Eq a where
  (==) :: a -> a -> Bool
instance Eq Int where x == y = primEqInt x y

매 결정 기준

상황	Approach
Container reuse	parametric <T>
Multiple impl 의 한 interface	trait / interface
Hot path, type set 작음	monomorphization (Rust, C++ template)
Heterogeneous collection	dyn Trait / interface{} / Box
Known finite variants	sum type (enum / discriminated union) — 매 generic 보다 simple

기본값: TS / Java 는 generics + interface, Rust 는 generic + trait (static dispatch).

🔗 Graph

• 부모: TypeScript 타입 시스템 (TypeScript Type System) · Polymorphism
• 변형: Subtype Polymorphism
• Adjacent: Variance · Sum Types

🤖 LLM 활용

언제: API surface design / type signature 의 reasoning / variance bug 진단. 언제 X: 매 simple concrete type 만 쓰는 곳에 generic 강제 — 매 over-abstraction.

❌ 안티패턴

• Generic for one caller: 매 YAGNI — 매 concrete 부터.
• Unbounded <T> 의 남용: 매 actually 필요한 constraint 누락.
• Variance 무시 (Java): List<Cat> 을 List<Animal> 자리에 — covariance bug.
• dyn Trait everywhere (Rust): 매 hot path 에서 vtable cost 누적.
• Type erasure 의 망각 (Java): runtime 에 T 의 reflection 시도.

🧪 검증 / 중복

• Verified (Pierce TAPL 2002, Rust Reference, TS Handbook 5.x, Go spec 1.21).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — TS/Rust/Go/Java generics + polymorphism 종류 정리