2nd/10_Wiki/Dev/Topic_PHP/PHP_OOP_Inheritance.md

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id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
php-oop-inheritance	PHP OOP Inheritance	Programming_Language	draft	conceptual		extends final keyword PHP 상속		B	0.9	2026-07-04	2026-07-04			php programming w3schools oop inheritance	https://www.w3schools.com/php/php_oop_inheritance.asp

PHP OOP Inheritance

🎯 한 줄 통찰 (One-line insight)

Calling a protected method from OUTSIDE the class fails, but calling that SAME protected method from WITHIN a subclass's own method (via $this->intro()) succeeds — the exact rule from access modifiers applies identically to methods, and the source proves it with a direct pass/fail comparison of the two call sites. [S1]

🧠 핵심 개념 (Core concepts)

• extends — inherits public and protected properties/methods from a parent class. [S1]
• Private members are NOT inherited — a child class cannot access a parent's private methods/properties at all. [S1]
• Method overriding — redefining a method with the same name in the child class replaces the parent's version. [S1]
• final on a class — prevents any class from extending it. [S1]
• final on a method — prevents child classes from overriding that specific method. [S1]

📖 세부 내용 (Details)

• Basic inheritance: class Fruit { public $name; public $color; public function __construct($name, $color) {...} public function intro() {...} } class Strawberry extends Fruit { public function message() {...} } $strawberry = new Strawberry("Strawberry", "red"); $strawberry->intro(); $strawberry->message(); — Strawberry uses Fruit's constructor/intro plus its own message(). [S1]
• Protected method fails from outside: $strawberry->intro(); // ERROR if intro() is protected. [S1]
• Protected method works from inside a child method: public function message() { $this->intro(); } — calling $this->intro() from within message() succeeds. [S1]
• Overriding: child class Strawberry redefines __construct() and intro() with the same names, completely replacing the parent's versions (adding a $weight property along the way). [S1]
• final prevents inheritance: final class Fruit {...} class Strawberry extends Fruit {...} // error. [S1]
• final prevents method override: class Fruit { final public function intro() {...} } class Strawberry extends Fruit { public function intro() {...} // error }. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• protected 메서드 호출 위치에 따른 성패: 클래스 외부에서 호출하면 에러, 파생 클래스 내부 메서드에서 $this로 호출하면 성공한다는 점이 두 대비 예제로 직접 증명됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — Strawberry가 Fruit의 생성자/메서드를 재정의(override)하며 weight 속성을 추가하는 것이 실전 오버라이딩의 대표 사례다. [S1]

💻 코드 패턴 (Code patterns)

Overriding a parent's constructor and method (PHP):

class Fruit {
    public $name;
    public $color;
    public function __construct($name, $color) { $this->name = $name; $this->color = $color; }
    public function intro() { echo "The fruit is $this->name and the color is $this->color."; }
}
class Strawberry extends Fruit {
    public $weight;
    public function __construct($name, $color, $weight) {
        $this->name = $name; $this->color = $color; $this->weight = $weight;
    }
    public function intro() {
        echo "A $this->name is $this->color, and the weight is $this->weight gram.";
    }
}

✅ 검증 상태 및 신뢰도

• 상태: draft
• 검증 단계: conceptual
• 출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
• 신뢰 점수: 0.90
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: PHP Tutorial
• 관련 개념: PHP OOP Access Modifiers, PHP OOP Constants, PHP OOP Classes Abstract
• 참조 맥락: 클래스 상속과 메서드 오버라이딩 — 클래스 상수(Constants) 챕터로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — PHP OOP - Inheritance — https://www.w3schools.com/php/php_oop_inheritance.asp

📝 변경 이력 (Change history)

• 2026-07-04: Initial draft synthesized from the W3Schools "PHP OOP Inheritance" page (Astra wiki-curation, P-Reinforce v3.1 format).