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PHP枚举与状态管理完全指南

PHP8.1正式引入了枚举类型。这是PHP类型系统的一个重要增强。枚举让状态管理更安全更清晰。今天说说枚举的使用。

枚举定义一组有限的可能值。

```php
enum OrderStatus
{
case Pending;
case Paid;
case Shipped;
case Delivered;
case Cancelled;
}

function processOrder(OrderStatus $status): string
{
return match ($status) {
OrderStatus::Pending => '待支付',
OrderStatus::Paid => '已支付',
OrderStatus::Shipped => '已发货',
OrderStatus::Delivered => '已签收',
OrderStatus::Cancelled => '已取消',
};
}

$status = OrderStatus::Paid;
echo processOrder($status) . "\n";
echo $status->name . "\n";
?>
>

字符串回退枚举可以存储到数据库。

```php
enum UserRole: string
{
case Admin = 'admin';
case Editor = 'editor';
case User = 'user';

public function label(): string
{
return match ($this) {
self::Admin => '管理员',
self::Editor => '编辑',
self::User => '普通用户',
};
}

public function permissions(): array
{
return match ($this) {
self::Admin => ['create', 'read', 'update', 'delete'],
self::Editor => ['create', 'read', 'update'],
self::User => ['read'],
};
}
}

$role = UserRole::from('admin');
echo $role->label() . "\n";
echo $role->can('delete') ? '有权限' : '无权限' . "\n";

foreach (UserRole::cases() as $role) {
echo "{$role->name}: {$role->value} - {$role->label()}\n";
}
?>

枚举在订单状态管理中的应用。

```php
enum PaymentStatus: string
{
case Pending = 'pending';
case Processing = 'processing';
case Completed = 'completed';
case Failed = 'failed';
case Refunded = 'refunded';

public function canRefund(): bool
{
return in_array($this, [self::Completed, self::Processing]);
}

public function isFinal(): bool
{
return in_array($this, [self::Completed, self::Failed, self::Refunded]);
}
}

class Payment
{
public function __construct(
public int $id,
public float $amount,
public PaymentStatus $status = PaymentStatus::Pending
) {}

public function complete(): void
{
if ($this->status !== PaymentStatus::Processing) throw new RuntimeException("不能完成");
$this->status = PaymentStatus::Completed;
}

public function refund(): void
{
if (!$this->status->canRefund()) throw new RuntimeException("不能退款");
$this->status = PaymentStatus::Refunded;
}
}

$payment = new Payment(1, 99.99);
$payment->status = PaymentStatus::Processing;
$payment->complete();
echo "状态: {$payment->status->value}\n";
echo "可退款: " . ($payment->status->canRefund() ? '是' : '否') . "\n";
?>
>

枚举让状态管理更加类型安全，避免了用字符串或整数表示状态时的拼写错误和无效值问题。枚举和数据库的配合也很自然，可以用value存储到数据库的字符串字段。