2nd/10_Wiki/Topics/Other/Inheritance-and-Polymorphism.md

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

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-inheritance-and-polymorphism	Inheritance and Polymorphism	10_Wiki/Topics	verified	self	OOP Inheritance Subtype Polymorphism Method Dispatch	none	A	0.95	applied	oop programming-language type-theory polymorphism		2026-05-10	pending	language framework multi oop

Inheritance and Polymorphism

매 한 줄

"매 inheritance 의 mechanism — polymorphism 의 outcome". 매 inheritance 의 code reuse + 매 is-a 의 subtype relationship; 매 polymorphism 의 same interface 의 different behavior. 매 modern 2026 의 view 의 "favor composition over inheritance" 의 default — Go/Rust 의 inheritance-free, but interface-polymorphism 의 universal. 매 LLM-generated code 의 over-inheritance 의 common antipattern.

매 핵심

매 inheritance 의 종류

• Single inheritance: 매 one parent class (Java, Kotlin, C#).
• Multiple inheritance: 매 N parents — diamond problem (C++, Python via MRO).
• Mixins / traits: 매 horizontal composition (Rust traits, Scala traits, Python mixins).
• Prototype-based: 매 object → object delegation (JavaScript, Lua).

매 polymorphism 의 종류

• Subtype polymorphism: 매 subclass 의 parent 의 substitute (Liskov LSP).
• Parametric polymorphism (generics): 매 type parameter — List<T>.
• Ad-hoc polymorphism (overloading): 매 same name 의 different signatures.
• Row polymorphism: 매 structural — TypeScript / OCaml 의 records.

매 응용

1. Domain hierarchy: 매 Animal → Dog/Cat. Often overused.
2. Plugin architecture: 매 Plugin interface + N implementations.
3. AST transformation: 매 Visitor pattern + node hierarchy.
4. Strategy pattern: 매 interchangeable algorithms via interface.

💻 패턴

매 subtype polymorphism (Python ABC + Liskov)

from abc import ABC, abstractmethod

class Shape(ABC):
    @abstractmethod
    def area(self) -> float: ...

class Circle(Shape):
    def __init__(self, r: float): self.r = r
    def area(self) -> float: return 3.14159 * self.r ** 2

class Rectangle(Shape):
    def __init__(self, w: float, h: float): self.w, self.h = w, h
    def area(self) -> float: return self.w * self.h

# Polymorphic use — caller knows nothing about concrete type
def total_area(shapes: list[Shape]) -> float:
    return sum(s.area() for s in shapes)

print(total_area([Circle(2), Rectangle(3, 4)]))  # 24.566...

매 composition over inheritance (modern preferred)

# ❌ Inheritance-heavy — fragile
class Animal:
    def move(self): print("move")
class Bird(Animal):
    def fly(self): print("fly")
class Penguin(Bird):  # Penguin 의 fly X — Liskov violation
    def fly(self): raise NotImplementedError

# ✅ Composition-based — flexible
from dataclasses import dataclass
from typing import Protocol

class Mover(Protocol):
    def move(self) -> str: ...

@dataclass
class Walker:
    def move(self) -> str: return "walk"

@dataclass
class Flyer:
    def move(self) -> str: return "fly"

@dataclass
class Animal2:
    name: str
    mover: Mover  # plug in capability — no inheritance

penguin = Animal2("Penguin", Walker())
sparrow = Animal2("Sparrow", Flyer())
print(penguin.mover.move(), sparrow.mover.move())

매 generic parametric polymorphism (TypeScript)

// Same code for any T
function head<T>(xs: T[]): T | undefined {
    return xs[0];
}

const n: number | undefined = head([1, 2, 3]);
const s: string | undefined = head(["a", "b"]);

// Bounded generic — T must be Comparable
interface Comparable<T> { compareTo(other: T): number; }

function max<T extends Comparable<T>>(xs: T[]): T {
    return xs.reduce((acc, x) => x.compareTo(acc) > 0 ? x : acc);
}

매 trait-based polymorphism (Rust — no inheritance)

trait Area {
    fn area(&self) -> f64;
}

struct Circle { r: f64 }
struct Square { side: f64 }

impl Area for Circle {
    fn area(&self) -> f64 { 3.14159 * self.r * self.r }
}
impl Area for Square {
    fn area(&self) -> f64 { self.side * self.side }
}

// Static dispatch (zero-cost generics)
fn print_area_static<T: Area>(s: &T) {
    println!("{}", s.area());
}

// Dynamic dispatch (vtable)
fn print_area_dyn(s: &dyn Area) {
    println!("{}", s.area());
}

fn main() {
    let shapes: Vec<Box<dyn Area>> = vec![
        Box::new(Circle { r: 2.0 }),
        Box::new(Square { side: 3.0 }),
    ];
    for s in &shapes { print_area_dyn(s.as_ref()); }
}

매 visitor pattern (AST traversal)

from dataclasses import dataclass
from typing import Union

# AST hierarchy
@dataclass
class Num: value: float
@dataclass
class Add: left: "Expr"; right: "Expr"
@dataclass
class Mul: left: "Expr"; right: "Expr"

Expr = Union[Num, Add, Mul]

# Polymorphic dispatch via match (Python 3.10+)
def evaluate(e: Expr) -> float:
    match e:
        case Num(v): return v
        case Add(l, r): return evaluate(l) + evaluate(r)
        case Mul(l, r): return evaluate(l) * evaluate(r)

# (3 + 4) * 5
print(evaluate(Mul(Add(Num(3), Num(4)), Num(5))))  # 35

매 LSP-violation 의 detector (mypy + tests)

# Runtime LSP check — for each subclass override, parameter contravariant + return covariant
import inspect
from typing import get_type_hints

def check_lsp(parent: type, child: type) -> list[str]:
    issues = []
    for name in dir(parent):
        if name.startswith("_") or not callable(getattr(parent, name)):
            continue
        try:
            p_hints = get_type_hints(getattr(parent, name))
            c_hints = get_type_hints(getattr(child, name))
        except Exception:
            continue
        # Return type must be subtype of parent's return
        if "return" in p_hints and "return" in c_hints:
            if not issubclass(c_hints["return"], p_hints["return"]):
                issues.append(f"{child.__name__}.{name}: return type widens parent")
    return issues

매 결정 기준

상황	Approach
매 is-a 의 stable	Inheritance OK — keep depth ≤ 2
매 has-a / can-do	Composition + protocol/interface
매 cross-cutting (logging, metrics)	Decorator / mixin / aspect
매 algorithm variants	Strategy pattern (composition)
매 type-safe collections	Parametric generics (List<T>)
매 closed AST / variant data	Sum types + pattern match (Rust enum, Scala sealed)

기본값: 매 composition + interface — inheritance 의 only when 명확 is-a + LSP-honoring.

🔗 Graph

• 부모: Object-Oriented-Programming · Type Theory
• 변형: Subtype Polymorphism · Parametric Polymorphism
• 응용: Visitor Pattern
• Adjacent: Composition over Inheritance · Duck Typing

🤖 LLM 활용

언제: 매 boilerplate 의 generation (interface + N impls) / 매 LSP audit / 매 inheritance-to-composition refactor. 언제 X: 매 deep inheritance design — 매 LLM 의 over-inherit 의 tendency. Manual review 필수.

❌ 안티패턴

• 매 deep inheritance: 매 4+ levels — fragile base class problem.
• 매 LSP violation: 매 subclass 의 throws on parent-supported method (Penguin.fly).
• 매 inheritance for code reuse only: 매 not is-a — use composition.
• 매 god parent class: 매 parent 의 every responsibility — SRP violation.
• 매 multiple inheritance 의 diamond ignore: 매 MRO 의 surprise behavior.

🧪 검증 / 중복

• Verified (Gamma et al. Design Patterns 1994; Liskov & Wing A Behavioral Notion of Subtyping 1994; Effective Java Item 18 "Favor composition" 2018).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — types of inheritance + polymorphism + multi-language patterns