PHP 枚举类型

PHP没有原声的枚举，从Java转过来的就懵逼了。那么怎么才能在PHP中使用枚举，而且又能被IDE识别呢。Constants（define）是一种办法，但是他是全局的，有命名空间冲突的问题。虽然数组没有命名空间问题，但是数组定义常量太模糊，而且运行时是可以被覆盖的，而且很少有IDE可以自动补全。

解决方案一

1.简单的用法

abstract class DaysOfWeek
{
    const Sunday = 0;
    const Monday = 1;
    // etc.
}

$today = DaysOfWeek::Sunday;

以上的方式很多情况下需要验证常量的值，以下的方法可以应用大部分场景

2.完善的用法

abstract class BasicEnum {
    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 isValidName($name, $strict = false) {
        $constants = self::getConstants();

        if ($strict) {
            return array_key_exists($name, $constants);
        }

        $keys = array_map('strtolower', array_keys($constants));
        return in_array(strtolower($name), $keys);
    }

    public static function isValidValue($value, $strict = true) {
        $values = array_values(self::getConstants());
        return in_array($value, $values, $strict);
    }
}
//应用场景
abstract class DaysOfWeek extends BasicEnum {
    const Sunday = 0;
    const Monday = 1;
    const Tuesday = 2;
    const Wednesday = 3;
    const Thursday = 4;
    const Friday = 5;
    const Saturday = 6;
}

DaysOfWeek::isValidName('Humpday');                  // false
DaysOfWeek::isValidName('Monday');                   // true
DaysOfWeek::isValidName('monday');                   // true
DaysOfWeek::isValidName('monday', $strict = true);   // false
DaysOfWeek::isValidName(0);                          // false

DaysOfWeek::isValidValue(0);                         // true
DaysOfWeek::isValidValue(5);                         // true
DaysOfWeek::isValidValue(7);                         // false
DaysOfWeek::isValidValue('Friday');                  // false

解决方案二

使用PHP Perl扩展中的SplEnum

<?php
class Month extends SplEnum {
    const __default = self::January;
    
    const January = 1;
    const February = 2;
    const March = 3;
    const April = 4;
    const May = 5;
    const June = 6;
    const July = 7;
    const August = 8;
    const September = 9;
    const October = 10;
    const November = 11;
    const December = 12;
}

echo new Month(Month::June) . PHP_EOL;

try {
    new Month(13);
} catch (UnexpectedValueException $uve) {
    echo $uve->getMessage() . PHP_EOL;
}
?>