---
id: php-oop-constants
title: "PHP OOP Constants"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["class constants", "scope resolution operator", "PHP 클래스 상수"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.89
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["php", "programming", "w3schools", "oop", "constants"]
raw_sources: ["https://www.w3schools.com/php/php_oop_constants.asp"]
applied_in: []
github_commit: ""
---

# [[PHP OOP Constants]]

## 🎯 한 줄 통찰 (One-line insight)
Class constants use TWO different keywords depending on whether you're inside or outside the class — `ClassName::CONSTANT` from outside, but `self::CONSTANT` from inside a method — even though both use the same `::` scope resolution operator, meaning the class-name vs. self choice signals your calling context. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Class constant** — declared with `const`; fixed value, cannot change once set; default visibility is `public`. [S1]
- **Case-sensitive but conventionally uppercase** — best practice names constants in ALL_CAPS. [S1]
- **Access from outside** — `ClassName::CONSTANT_NAME`. [S1]
- **Access from inside** — `self::CONSTANT_NAME`. [S1]

## 📖 세부 내용 (Details)
- Outside access: `class Goodbye { const MESSAGE = "Thank you for visiting W3Schools.com!"; } echo Goodbye::MESSAGE;`. [S1]
- Inside access (self): `class Goodbye { const MESSAGE = "..."; public function bye() { echo self::MESSAGE; } } $goodbye = new Goodbye(); $goodbye->bye();`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
소스에서 모순되는 정보는 발견되지 않음.

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 클래스 상수는 정적 메서드/속성 챕터에서 사용하는 :: 연산자를 먼저 익히는 단계다. [S1]

## 💻 코드 패턴 (Code patterns)
Accessing a class constant from inside via self:: (PHP):
```php
class Goodbye {
    const MESSAGE = "Thank you for visiting W3Schools.com!";
    public function bye() {
        echo self::MESSAGE;
    }
}
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.89
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[PHP Tutorial]]
- **관련 개념:** [[PHP OOP Inheritance]], [[PHP OOP Classes Abstract]], [[PHP OOP Static Properties]]
- **참조 맥락:** :: 연산자를 이용한 클래스 상수 접근 — 추상 클래스(Abstract Classes) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — PHP OOP - Class Constants — https://www.w3schools.com/php/php_oop_constants.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "PHP OOP Class Constants" page (Astra wiki-curation, P-Reinforce v3.1 format).