PHP 8 现代特性实战：枚举、只读类、构造器属性提升与强类型体系

function formatAmount(int|float $amount): string
{
    return number_format($amount, 2);
}

// ❌ 类型逃避
function log(mixed $data): mixed { return $data; }

// ✅ 明确契约
function log(string|array $data): void { /* ... */ }

function throwIfInvalid(array $data): never
{
    throw new InvalidArgumentException('数据非法');
}

function same(Countable&Traversable $c): static
{
    return $c;   // 返回子类型自身
}

function createUser(
    string $name,
    string $email,
    string $role = 'member',
    bool $active = true,
): array { /* ... */ }

createUser('李雷', 'lei@example.com', role: 'admin', active: false);

$params = ['name' => '韩梅梅', 'email' => 'mei@example.com'];
createUser(...$params);   // 数组展开为命名参数

// PHP 7 时代：7 行样板
class User
{
    private string $name;
    public function __construct(string $name, private string $email)
    {
        $this->name = $name;
    }
}

// PHP 8：提升语法，一行完成声明+赋值
class User
{
    public function __construct(
        public readonly string $name,
        public string $email,
    ) {}
}

class Config
{
    public function __construct(
        public string $key,
        public string $value = '',
        private ?string $secret = null,
    ) {}
}

$status = match ($code) {
    200 => 'OK',
    404 => 'Not Found',
    500 => 'Server Error',
    default => 'Unknown',
};

// 相比 switch：无穿透(fall-through)、自动返回、严格类型

$bucket = match (true) {
    $age < 18         => '未成年',
    $age >= 18 && $age < 60 => '成年',
    default           => '老年',
};

// PHP 7：层层判空
$country = $user->address ? $user->address->country : null;

// PHP 8：?-> 空安全链
$country = $user->address?->country;

// 更深的链
$phone = $user->profile?->contact?->phone;

$config['retries'] ??= 3;      // 未定义/为 null 时赋默认

$value = $repo->find($id)?->price ?? 0.0;

enum PaymentStatus
{
    case Pending;
    case Paid;
    case Refunded;
}

$status = PaymentStatus::Paid;
echo $status->name;       // 'Paid'

enum OrderState: string
{
    case Created  = 'created';
    case Shipped  = 'shipped';
    case Delivered = 'delivered';
    case Cancelled = 'cancelled';

    public function label(): string
    {
        return match ($this) {
            self::Created    => '已创建',
            self::Shipped    => '已发货',
            self::Delivered  => '已送达',
            self::Cancelled  => '已取消',
        };
    }
}

OrderState::from('shipped');   // 从字符串反解
OrderState::tryFrom('nope');   // 反解失败返回 null

interface HasColor
{
    public function color(): string;
}

enum Priority: int implements HasColor
{
    case Low  = 1;  public function color(): string { return 'green'; }
    case High = 2;  public function color(): string { return 'red'; }
}

class User
{
    public function __construct(
        public readonly int $id,
        public readonly string $email,
    ) {}
}

// $user->email = 'x';  // 抛 Error：不能修改只读属性

readonly class OrderItem
{
    public function __construct(
        public string $sku,
        public int $qty,
        public float $price,
    ) {}
}

$strlen = strlen(...);
echo $strlen('hello');        // 5

$upper = strtoupper(...);
array_map($upper, ['a', 'b']); // ['A','B']

function config(
    Logger $logger = new ConsoleLogger(),   // 默认值里 new
): void { /* ... */ }

$letters = str_split('ab c');
// 可直接用作列表解构
[$a, $b] = $letters;

# 1. 先升级到 PHP 7.4（最低），加 declare(strict_types=1) 逐步收窄
# 2. 用 php8 兼容检查工具扫描
composer require --dev php-parallel-lint/php-parallel-lint
vendor/bin/parallel-lint src tests

# 3. 启用 PHPStan/PHP-CS-Fixer 提高类型与风格下限
composer require --dev phpstan/phpstan
vendor/bin/phpstan analyse --level=6 src

# 4. 逐个模块切到 PHP 8，修完回归再切下一模块

declare(strict_types=1);   // 文件顶部强制严格类型

// 接口优先，配合枚举与只读类，写出「编译期可检查」的领域模型
interface PaymentProcessor
{
    public function process(Order $order): PaymentResult;
}