2nd/10_Wiki/Topics/Domain_Programming/Topic_PHP/PHP_Functions.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-functions	PHP Functions	Programming_Language	draft	conceptual		variadic functions strict_types PHP 함수		B	0.9	2026-07-04	2026-07-04			php programming w3schools functions	https://www.w3schools.com/php/php_functions.asp

PHP Functions

🎯 한 줄 통찰 (One-line insight)

The ... variadic operator can ONLY be the LAST parameter — putting it first (function myFamily(...$firstname, $lastname)) is explicitly shown as an ERROR case, because a variadic parameter greedily collects all remaining arguments into an array, leaving nothing for any parameter declared after it. [S1]

🧠 핵심 개념 (Core concepts)

• 1000+ built-in functions available directly. [S1]
• User-defined function — function name($params) { ...; return $value; }; not case-sensitive; not auto-run (must be called). [S1]
• Default parameter values — function setHeight($height = 50) {...} — used when the argument is omitted. [S1]
• Pass by reference — function add_five(&$value) { $value += 5; } — the & makes changes persist back to the caller's variable (default is pass-by-value, a copy). [S1]
• Variadic functions (...) — function sumMyNumbers(...$x) {...} — accepts an unknown number of arguments, collected into an array; must be the LAST parameter. [S1]
• Loosely typed by default — no type declarations required. [S1]
• declare(strict_types=1); (PHP 7+) — must be the FIRST line of the file; enforces strict type checking, throwing a Fatal Error on type mismatch. [S1]
• Return type declarations — function addNumbers(float $a, float $b) : float {...} — colon syntax before the opening brace. [S1]

📖 세부 내용 (Details)

• Default parameter: function setHeight($height = 50) { echo "The height is : $height <br>"; } setHeight(350); setHeight(); // uses default 50. [S1]
• Pass by reference: function add_five(&$value) { $value += 5; } $num = 2; add_five($num); echo $num; // 7. [S1]
• Variadic (valid, last position): function sumMyNumbers(...$x) { $n = 0; $len = count($x); for($i = 0; $i < $len; $i++) { $n += $x[$i]; } return $n; }. [S1]
• Variadic (invalid, first position — errors): function myFamily(...$firstname, $lastname) {...} // error: variadic must be last. [S1]
• Strict types: <?php declare(strict_types=1); function addNumbers(int $a, int $b) { return $a + $b; } echo addNumbers(5, "5 days"); // Fatal Error — "5 days" is not an int. [S1]
• Return type declaration: function addNumbers(float $a, float $b) : float { return $a + $b; }. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• 가변 인자의 위치 제약: ... 연산자를 사용하는 매개변수는 반드시 마지막에 위치해야 하며, 그렇지 않으면 에러가 발생한다는 점이 실패 예제로 직접 검증됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 개수가 정해지지 않은 숫자들의 합을 구하는 가변 인자 함수(sumMyNumbers)가 실전 활용의 대표 사례다. [S1]

💻 코드 패턴 (Code patterns)

Variadic function summing an unknown number of arguments (PHP):

function sumMyNumbers(...$x) {
    $n = 0;
    $len = count($x);
    for ($i = 0; $i < $len; $i++) {
        $n += $x[$i];
    }
    return $n;
}
$a = sumMyNumbers(5, 2, 6, 2, 7, 7);
echo $a;

✅ 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, PHP OOP Classes Objects, PHP Callback Functions
• 참조 맥락: 함수 정의/호출의 전체 문법 — 배열(Arrays) 챕터로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — PHP Functions — https://www.w3schools.com/php/php_functions.asp

📝 변경 이력 (Change history)

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