PHP 類別宣告與實例化、建構子與解構子完整教學

基本類別結構

name} is crying...\n";
    }
    
    // 建構子：new 時自動呼叫
    public function __construct(string $name = 'Anonymous', int $age = 0) {
        $this->name = $name;
        $this->age = $age;
        echo "{$this->name} 對象生成啦\n";
    }
    
    // 解構子：物件銷毀時自動呼叫
    public function __destruct() {
        echo "{$this->name} 對象銷毀啦\n";
    }
}

// 實例化
$leo = new Human('Leo', 25);
$tim = new Human('Tim', 18);

echo "--- 手動銷毀 ---\n";
unset($leo);  // 顯式銷毀

echo "--- 腳本結束隱式銷毀 ---\n";
// $tim 此處自動銷毀

/* 輸出順序：
Leo 對象生成啦
Tim 對象生成啦
--- 手動銷毀 ---
Leo 對象銷毀啦
--- 腳本結束隱式銷毀 ---
Tim 對象銷毀啦
*/

存取修飾符

class Example {
    public $pub = 1;
    protected $pro = 2;
    private $pri = 3;
    
    public function show() {
        echo $this->pub;   // ✅
        echo $this->pro;   // ✅
        echo $this->pri;   // ✅
    }
}

class Child extends Example {
    public function test() {
        echo $this->pub;   // ✅
        echo $this->pro;   // ✅
        // echo $this->pri; // ❌ Fatal Error
    }
}

$obj = new Example();
echo $obj->pub;    // ✅
// echo $obj->pro;  // ❌
// echo $obj->pri;  // ❌

靜態成員 vs 實例成員

class Counter {
    public static int $staticCount = 0;   // 類別層級
    public int $instanceCount = 0;        // 物件層級
    
    public function increment(): void {
        self::$staticCount++;      // 靜態用 self::
        $this->instanceCount++;    // 實例用 $this->
    }
    
    public static function getStatic(): int {
        return self::$staticCount;
    }
}

$a = new Counter();
$b = new Counter();
$a->increment();
$b->increment();
echo Counter::getStatic();      // 2 (共享)
echo $a->instanceCount;         // 1 (獨立)
echo $b->instanceCount;         // 1 (獨立)

建構子進階用法

1. 建構子提升屬性

// PHP 8.0+
class User {
    public function __construct(
        public string $name,
        public string $email,
        protected string $passwordHash,
        private int $id = 0
    ) {}
}

$user = new User('Leo', 'leo@example.com', 'hashed_pwd');
echo $user->name;  // Leo

2. 多建構子模式 (靜態工廠方法)

class DateTime {
    private int $timestamp;
    
    private function __construct(int $ts) {
        $this->timestamp = $ts;
    }
    
    public static function now(): self {
        return new self(time());
    }
    
    public static function fromString(string $date): self {
        return new self(strtotime($date));
    }
    
    public static function fromTimestamp(int $ts): self {
        return new self($ts);
    }
}

$dt1 = DateTime::now();
$dt2 = DateTime::fromString('2024-01-01');
$dt3 = DateTime::fromTimestamp(1704067200);

3. 依賴注入

class OrderService {
    public function __construct(
        private PaymentGateway $gateway,
        private LoggerInterface $logger,
        private EventDispatcher $dispatcher
    ) {}
}

解構子最佳實踐

• 釋放資源：關閉資料庫連線、檔案控制代碼、cURL handle
• 不要在解構子拋出例外 (PHP 會忽略並產生 Fatal Error)
• 避免執行耗時操作 (關閉連線通常足夠)
• 循環參考時解構順序不確定，考慮 __destruct 內 gc_collect_cycles()

物件複製與複製控制

class Document {
    public string $title;
    private array $metadata;
    
    public function __construct(string $title) {
        $this->title = $title;
        $this->metadata = ['created' => time()];
    }
    
    // 淺拷貝預設行為：基本型別複製，物件參考同一實例
    // 深拷貝自定義
    public function __clone() {
        $this->metadata = $this->metadata;  // 陣列自動深拷貝
        // 若有物件屬性：$this->child = clone $this->child;
    }
}

$doc1 = new Document('Report');
$doc2 = clone $doc1;
$doc2->title = 'Report v2';

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