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10_Wiki/Dev/Topic_PHP/PHP_Looping_Foreach.md

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+---
+id: php-looping-foreach
+title: "PHP Looping Foreach"
+category: "Programming_Language"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["foreach loop", "byref", "PHP foreach 반복문"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.9
+created_at: 2026-07-04
+updated_at: 2026-07-04
+review_reason: ""
+merge_history: []
+tags: ["php", "programming", "w3schools", "loops", "foreach", "arrays"]
+raw_sources: ["https://www.w3schools.com/php/php_looping_foreach.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[PHP Looping Foreach]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+By default, modifying the loop variable inside `foreach` does NOT affect the original array — but adding a single `&` (`foreach ($colors as &$x)`) switches to by-reference assignment, meaning changes to `$x` inside the loop DO mutate `$colors` directly, a one-character difference with a completely different mutation contract. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **`foreach ($array as $value)`** — loops over indexed array values. [S1]
+- **`foreach ($array as $key => $value)`** — loops over associative arrays, exposing both key and value. [S1]
+- **Works on objects too** — iterates over public properties (`$name => $value`). [S1]
+- **By-value default** — modifying the loop variable does not change the source array. [S1]
+- **By-reference (`&$x`)** — modifying the loop variable DOES change the source array. [S1]
+- **`break`** / **`continue`** — same semantics as other loops. [S1]
+- **Alternative syntax** — `foreach (...) : ... endforeach;`. [S1]
+
+## 📖 세부 내용 (Details)
+- Indexed array: `$colors = array("red", "green", "blue", "yellow"); foreach ($colors as $value) { echo "$value <br>"; }`. [S1]
+- Associative array: `$members = array("Peter"=>"35", "Ben"=>"37", "Joe"=>"43"); foreach ($members as $key => $value) { echo "$key : $value <br>"; }`. [S1]
+- Object properties: `foreach ($myCar as $x => $y) { echo "$x: $y <br>"; }`. [S1]
+- By-value (no mutation): `foreach ($colors as $x) { if ($x == "blue") $x = "pink"; } // $colors unchanged`. [S1]
+- By-reference (mutates original): `foreach ($colors as &$x) { if ($x == "blue") $x = "pink"; } // $colors now has "pink" instead of "blue"`. [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+- **참조 전달의 예외적 동작**: 기본적으로 반복 변수 수정은 원본 배열에 영향을 주지 않지만, &를 붙이면 원본이 실제로 변경된다는 점이 두 예제로 명확히 대비됨. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+현재 발견된 실제 적용 사례가 없습니다 — 배열 값을 순회하며 특정 조건에 따라 원본을 직접 수정해야 할 때 &$x 참조 전달이 사용된다. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+By-reference foreach mutates the original array (PHP):
+```php
+$colors = array("red", "green", "blue", "yellow");
+foreach ($colors as &$x) {
+    if ($x == "blue") $x = "pink";
+}
+var_dump($colors); // "blue" is now "pink" in the original array
+```
+
+## ✅ 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 Looping For]], [[PHP Arrays]], [[PHP OOP Classes Objects]]
+- **참조 맥락:** 배열/객체 순회 전용 반복문 — break/continue 챕터로 이어짐.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — PHP foreach Loop — https://www.w3schools.com/php/php_looping_foreach.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "PHP foreach Loop" page (Astra wiki-curation, P-Reinforce v3.1 format).