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PHP 使用常量实现枚举类

<?php
abstract class Enum {
    private static $constCacheArray = NULL;

    private static function getConstants() {
        if (self::$constCacheArray == NULL) {
            self::$constCacheArray = [];
        }
        $calledClass = get_called_class();
        if (!array_key_exists($calledClass, self::$constCacheArray)) {
            $reflect = new ReflectionClass($calledClass);
            self::$constCacheArray[$calledClass] = $reflect->getConstants();
        }
        return self::$constCacheArray[$calledClass];
    }

    public static function getEnumValue($constant) {
        $constants = self::getConstants();
        return $constants[$constant] ?? null;
    }
}

class StatusCode extends Enum {
    const OK = 200;
    const NOT_FOUND = 404;
    // ... 其他状态码
}

// 使用类常量直接访问枚举值
$statusCode = StatusCode::getEnumValue(StatusCode::OK);
echo $statusCode; // 输出 200