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

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

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-arrays-update	PHP Arrays Update	Programming_Language	draft	conceptual		PHP 배열 수정		B	0.9	2026-07-04	2026-07-04			php programming w3schools arrays update unset	https://www.w3schools.com/php/php_arrays_update.asp

PHP Arrays Update

🎯 한 줄 통찰 (One-line insight)

Forgetting unset($x) after a by-reference foreach loop is a genuine bug trap — the source demonstrates it directly: after the loop, $x STILL points at the array's last element, so a later $x = "ice cream"; silently overwrites that last array element too, even though the loop has already finished. [S1]

🧠 핵심 개념 (Core concepts)

• Update by index/key — same syntax as access: $cars[1] = "Ford"; or $cars["year"] = 2024;. [S1]
• By-reference foreach for bulk update — foreach ($cars as &$x) { $x = "Ford"; } mutates every element of the original array. [S1]
• unset($x) after the loop is mandatory — without it, $x remains a reference to the array's last element, and any later reassignment of $x silently corrupts that array element. [S1]

📖 세부 내용 (Details)

• Basic index update: $cars = array("Volvo", "BMW", "Toyota"); $cars[1] = "Ford";. [S1]
• Basic key update: $cars = array("brand" => "Ford", ...); $cars["year"] = 2024;. [S1]
• Bulk by-reference update: foreach ($cars as &$x) { $x = "Ford"; } unset($x); — all items become "Ford". [S1]
• Bug demonstration (unset omitted): foreach ($cars as &$x) { $x = "Ford"; } $x = "ice cream"; var_dump($cars); // last element of $cars is now "ice cream"!. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• unset() 생략의 위험: 참조 반복 후 unset()을 호출하지 않으면 $x가 배열의 마지막 요소를 계속 참조하며, 이후 $x를 재할당하면 배열이 의도치 않게 변경된다는 점이 버그 예제로 직접 증명됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — foreach 참조 반복 후 unset()을 빠뜨리는 것이 실전에서 자주 발생하는 버그 패턴이므로 반드시 기억해야 한다. [S1]

💻 코드 패턴 (Code patterns)

Forgetting unset() after a by-reference loop corrupts the array (PHP):

$cars = array("Volvo", "BMW", "Toyota");
foreach ($cars as &$x) {
    $x = "Ford";
}
$x = "ice cream"; // BUG: $x still references $cars' last element!
var_dump($cars);  // last element is now "ice cream", not "Ford"

✅ 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 Arrays Access, PHP Looping Foreach, PHP Arrays Add
• 참조 맥락: 배열 항목 수정 — 항목 추가(Add) 챕터로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — PHP Update Array Items — https://www.w3schools.com/php/php_arrays_update.asp

📝 변경 이력 (Change history)

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