我知道PHP还没有本地枚举。但是我已经习惯了来自Java世界的它们。我喜欢使用枚举来提供ide的自动补全功能能够理解的预定义值。

常量可以解决这个问题,但是存在名称空间冲突问题,而且(实际上是因为)它们是全局的。数组没有名称空间的问题,但是它们太模糊了,它们可以在运行时被覆盖,而且ide很少知道如何在没有额外的静态分析注释或属性的情况下自动填充它们的键。

你有什么常用的解决方案/变通办法吗?有人记得PHP的人对枚举有什么想法或决定吗?


当前回答

下面的Enum类定义是强类型的,使用和定义都很自然。

定义:

class Fruit extends Enum {
    static public $APPLE = 1;
    static public $ORANGE = 2;
}
Fruit::initialize(); //Can also be called in autoloader

切换Enum

$myFruit = Fruit::$APPLE;

switch ($myFruit) {
    case Fruit::$APPLE  : echo "I like apples\n";  break;
    case Fruit::$ORANGE : echo "I hate oranges\n"; break;
}

>> I like apples

传递Enum作为参数(强类型)

/** Function only accepts Fruit enums as input**/
function echoFruit(Fruit $fruit) {
    echo $fruit->getName().": ".$fruit->getValue()."\n";
}

/** Call function with each Enum value that Fruit has */
foreach (Fruit::getList() as $fruit) {
    echoFruit($fruit);
}

//Call function with Apple enum
echoFruit(Fruit::$APPLE)

//Will produce an error. This solution is strongly typed
echoFruit(2);

>> APPLE: 1
>> ORANGE: 2
>> APPLE: 1
>> Argument 1 passed to echoFruit() must be an instance of Fruit, integer given

以字符串形式返回Enum

echo "I have an $myFruit\n";

>> I have an APPLE

通过整数获取Enum

$myFruit = Fruit::getByValue(2);

echo "Now I have an $myFruit\n";

>> Now I have an ORANGE

按名称获取Enum

$myFruit = Fruit::getByName("APPLE");

echo "But I definitely prefer an $myFruit\n\n";

>> But I definitely prefer an APPLE

枚举类:

/**
 * @author Torge Kummerow
 */
class Enum {

    /**
     * Holds the values for each type of Enum
     */
    static private $list = array();

    /**
     * Initializes the enum values by replacing the number with an instance of itself
     * using reflection
     */
    static public function initialize() {
        $className = get_called_class();
        $class = new ReflectionClass($className);
        $staticProperties = $class->getStaticProperties();

        self::$list[$className] = array();

        foreach ($staticProperties as $propertyName => &$value) {
            if ($propertyName == 'list')
                continue;

            $enum = new $className($propertyName, $value);
            $class->setStaticPropertyValue($propertyName, $enum);
            self::$list[$className][$propertyName] = $enum;
        } unset($value);
    }


    /**
     * Gets the enum for the given value
     *
     * @param integer $value
     * @throws Exception
     *
     * @return Enum
     */
    static public function getByValue($value) {
        $className = get_called_class();
        foreach (self::$list[$className] as $propertyName=>&$enum) {
            /* @var $enum Enum */
            if ($enum->value == $value)
                return $enum;
        } unset($enum);

        throw new Exception("No such enum with value=$value of type ".get_called_class());
    }

    /**
     * Gets the enum for the given name
     *
     * @param string $name
     * @throws Exception
     *
     * @return Enum
     */
    static public function getByName($name) {
        $className = get_called_class();
        if (array_key_exists($name, static::$list[$className]))
            return self::$list[$className][$name];

        throw new Exception("No such enum ".get_called_class()."::\$$name");
    }


    /**
     * Returns the list of all enum variants
     * @return Array of Enum
     */
    static public function getList() {
        $className = get_called_class();
        return self::$list[$className];
    }


    private $name;
    private $value;

    public function __construct($name, $value) {
        $this->name = $name;
        $this->value = $value;
    }

    public function __toString() {
        return $this->name;
    }

    public function getValue() {
        return $this->value;
    }

    public function getName() {
        return $this->name;
    }

}

除了

当然,您也可以为ide添加注释

class Fruit extends Enum {

    /**
     * This comment is for autocomplete support in common IDEs
     * @var Fruit A yummy apple
     */
    static public $APPLE = 1;

    /**
     * This comment is for autocomplete support in common IDEs
     * @var Fruit A sour orange
     */
    static public $ORANGE = 2;
}

//This can also go to the autoloader if available.
Fruit::initialize();

其他回答

我使用接口而不是类:

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

var $today = DaysOfWeek::Sunday;

最后,PHP 7.1+给出了一个不能被重写的常量。

/**
 * An interface that groups HTTP Accept: header Media Types in one place.
 */
interface MediaTypes
{
    /**
    * Now, if you have to use these same constants with another class, you can
    * without creating funky inheritance / is-a relationships.
    * Also, this gets around the single inheritance limitation.
    */

    public const HTML = 'text/html';
    public const JSON = 'application/json';
    public const XML = 'application/xml';
    public const TEXT = 'text/plain';
}

/**
 * An generic request class.
 */
abstract class Request
{
    // Why not put the constants here?
    // 1) The logical reuse issue.
    // 2) Single Inheritance.
    // 3) Overriding is possible.

    // Why put class constants here?
    // 1) The constant value will not be necessary in other class families.
}

/**
 * An incoming / server-side HTTP request class.
 */
class HttpRequest extends Request implements MediaTypes
{
    // This class can implement groups of constants as necessary.
}

如果您使用的是名称空间,那么代码补全应该可以工作。

但是,这样做将失去在类族(protected)或单独在类(private)中隐藏常量的能力。根据定义,接口中的所有内容都是公共的。

PHP手册:接口

更新:

PHP 8.1现在有了枚举。

我所见过的PHP中枚举最常见的解决方案是创建一个通用枚举类,然后扩展它。你可以看看这个。

更新:或者,我从phpclasses.org找到了这个。

一个不使用反射的更简单、更轻的版本:

abstract class enum {
    private function __construct() {}
    static function has($const) {
        $name = get_called_class();
        return defined("$name::$const");
    }
    static function value($const) {
        $name = get_called_class();
        return defined("$name::$const")? constant("$name::$const") : false;
    }
}

用法:

class requestFormat  extends enum { const HTML = 1; const JSON = 2; const XML  = 3; const FORM = 4; }

echo requestFormat::value('JSON'); // 2
echo requestFormat::has('JSON');   // true

这提供了常量的优势,也允许检查它们的有效性,但它缺乏更复杂的解决方案所提供的其他花哨功能,更明显的是无法检查值的反向(在上面的例子中,你不能检查'2'是否是一个有效值)

下面是一个github库,用于在php中处理类型安全的枚举:

这个库处理类生成、类缓存,并实现了Type Safe Enumeration设计模式,使用几个辅助方法来处理枚举,比如为枚举排序检索序号,或为枚举组合检索二进制值。

生成的代码使用一个普通的旧php模板文件,该文件也是可配置的,因此您可以提供自己的模板。

它是由phpunit覆盖的完整测试。

Php-enums在github (feel free to fork)

用法:(@参见Usage .php或单元测试了解更多细节)

<?php
//require the library
require_once __DIR__ . '/src/Enum.func.php';

//if you don't have a cache directory, create one
@mkdir(__DIR__ . '/cache');
EnumGenerator::setDefaultCachedClassesDir(__DIR__ . '/cache');

//Class definition is evaluated on the fly:
Enum('FruitsEnum', array('apple' , 'orange' , 'rasberry' , 'bannana'));

//Class definition is cached in the cache directory for later usage:
Enum('CachedFruitsEnum', array('apple' , 'orange' , 'rasberry' , 'bannana'), '\my\company\name\space', true);

echo 'FruitsEnum::APPLE() == FruitsEnum::APPLE(): ';
var_dump(FruitsEnum::APPLE() == FruitsEnum::APPLE()) . "\n";

echo 'FruitsEnum::APPLE() == FruitsEnum::ORANGE(): ';
var_dump(FruitsEnum::APPLE() == FruitsEnum::ORANGE()) . "\n";

echo 'FruitsEnum::APPLE() instanceof Enum: ';
var_dump(FruitsEnum::APPLE() instanceof Enum) . "\n";

echo 'FruitsEnum::APPLE() instanceof FruitsEnum: ';
var_dump(FruitsEnum::APPLE() instanceof FruitsEnum) . "\n";

echo "->getName()\n";
foreach (FruitsEnum::iterator() as $enum)
{
  echo "  " . $enum->getName() . "\n";
}

echo "->getValue()\n";
foreach (FruitsEnum::iterator() as $enum)
{
  echo "  " . $enum->getValue() . "\n";
}

echo "->getOrdinal()\n";
foreach (CachedFruitsEnum::iterator() as $enum)
{
  echo "  " . $enum->getOrdinal() . "\n";
}

echo "->getBinary()\n";
foreach (CachedFruitsEnum::iterator() as $enum)
{
  echo "  " . $enum->getBinary() . "\n";
}

输出:

FruitsEnum::APPLE() == FruitsEnum::APPLE(): bool(true)
FruitsEnum::APPLE() == FruitsEnum::ORANGE(): bool(false)
FruitsEnum::APPLE() instanceof Enum: bool(true)
FruitsEnum::APPLE() instanceof FruitsEnum: bool(true)
->getName()
  APPLE
  ORANGE
  RASBERRY
  BANNANA
->getValue()
  apple
  orange
  rasberry
  bannana
->getValue() when values have been specified
  pig
  dog
  cat
  bird
->getOrdinal()
  1
  2
  3
  4
->getBinary()
  1
  2
  4
  8