这里的其他一些答案中缺少的一个方面是使用带有类型提示的枚举的方法。

如果您将枚举定义为抽象类中的一组常量，例如。

abstract class ShirtSize {
    public const SMALL = 1;
    public const MEDIUM = 2;
    public const LARGE = 3;
}

那么你就不能在函数参数中输入提示，一方面是因为它是不可实例化的，另一方面是因为ShirtSize::SMALL的类型是int，而不是ShirtSize。

这就是为什么PHP中的本地枚举比我们能想到的任何东西都要好得多。但是，我们可以通过保留一个表示枚举值的私有属性来近似枚举，然后将该属性的初始化限制为预定义的常量。为了防止枚举被任意实例化(没有白名单类型检查的开销)，我们将构造函数设为private。

class ShirtSize {
    private $size;
    private function __construct ($size) {
        $this->size = $size;
    }
    public function equals (ShirtSize $s) {
        return $this->size === $s->size;
    }
    public static function SMALL () { return new self(1); }
    public static function MEDIUM () { return new self(2); }
    public static function LARGE () { return new self(3); }
}

然后我们可以像这样使用ShirtSize:

function sizeIsAvailable ($productId, ShirtSize $size) {
    // business magic
}
if(sizeIsAvailable($_GET["id"], ShirtSize::LARGE())) {
    echo "Available";
} else {
    echo "Out of stock.";
}
$s2 = ShirtSize::SMALL();
$s3 = ShirtSize::MEDIUM();
echo $s2->equals($s3) ? "SMALL == MEDIUM" : "SMALL != MEDIUM";

这样，从用户的角度来看，最大的区别是必须在常量的名称上附加一个()。

一个缺点是===(比较对象是否相等)将在==返回true时返回false。出于这个原因，最好提供一个equals方法，这样用户就不必记得使用==和not ===来比较两个enum值。

编辑:现有的几个答案非常相似，特别是:https://stackoverflow.com/a/25526473/2407870。

四年后，我又遇到了这个。我目前的方法是这样的，因为它允许在IDE中完成代码以及类型安全:

基类:

abstract class TypedEnum
{
    private static $_instancedValues;

    private $_value;
    private $_name;

    private function __construct($value, $name)
    {
        $this->_value = $value;
        $this->_name = $name;
    }

    private static function _fromGetter($getter, $value)
    {
        $reflectionClass = new ReflectionClass(get_called_class());
        $methods = $reflectionClass->getMethods(ReflectionMethod::IS_STATIC | ReflectionMethod::IS_PUBLIC);    
        $className = get_called_class();

        foreach($methods as $method)
        {
            if ($method->class === $className)
            {
                $enumItem = $method->invoke(null);

                if ($enumItem instanceof $className && $enumItem->$getter() === $value)
                {
                    return $enumItem;
                }
            }
        }

        throw new OutOfRangeException();
    }

    protected static function _create($value)
    {
        if (self::$_instancedValues === null)
        {
            self::$_instancedValues = array();
        }

        $className = get_called_class();

        if (!isset(self::$_instancedValues[$className]))
        {
            self::$_instancedValues[$className] = array();
        }

        if (!isset(self::$_instancedValues[$className][$value]))
        {
            $debugTrace = debug_backtrace();
            $lastCaller = array_shift($debugTrace);

            while ($lastCaller['class'] !== $className && count($debugTrace) > 0)
            {
                $lastCaller = array_shift($debugTrace);
            }

            self::$_instancedValues[$className][$value] = new static($value, $lastCaller['function']);
        }

        return self::$_instancedValues[$className][$value];
    }

    public static function fromValue($value)
    {
        return self::_fromGetter('getValue', $value);
    }

    public static function fromName($value)
    {
        return self::_fromGetter('getName', $value);
    }

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

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

枚举例子:

final class DaysOfWeek extends TypedEnum
{
    public static function Sunday() { return self::_create(0); }    
    public static function Monday() { return self::_create(1); }
    public static function Tuesday() { return self::_create(2); }   
    public static function Wednesday() { return self::_create(3); }
    public static function Thursday() { return self::_create(4); }  
    public static function Friday() { return self::_create(5); }
    public static function Saturday() { return self::_create(6); }      
}

使用示例:

function saveEvent(DaysOfWeek $weekDay, $comment)
{
    // store week day numeric value and comment:
    $myDatabase->save('myeventtable', 
       array('weekday_id' => $weekDay->getValue()),
       array('comment' => $comment));
}

// call the function, note: DaysOfWeek::Monday() returns an object of type DaysOfWeek
saveEvent(DaysOfWeek::Monday(), 'some comment');

注意，同一个枚举条目的所有实例都是相同的:

$monday1 = DaysOfWeek::Monday();
$monday2 = DaysOfWeek::Monday();
$monday1 === $monday2; // true

你也可以在switch语句中使用它:

function getGermanWeekDayName(DaysOfWeek $weekDay)
{
    switch ($weekDay)
    {
        case DaysOfWeek::Monday(): return 'Montag';
        case DaysOfWeek::Tuesday(): return 'Dienstag';
        // ...
}

你也可以通过名称或值创建枚举项:

$monday = DaysOfWeek::fromValue(2);
$tuesday = DaysOfWeek::fromName('Tuesday');

或者你可以从一个现有的枚举条目中获取名称(即函数名):

$wednesday = DaysOfWeek::Wednesday()
echo $wednesDay->getName(); // Wednesday

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

我已经开始使用下面的方法，因为它使我能够对函数参数具有类型安全，在NetBeans中自动完成和良好的性能。我不太喜欢的一件事是你必须调用[扩展类名]::enumerate();在定义类之后。

abstract class Enum {

    private $_value;

    protected function __construct($value) {
        $this->_value = $value;
    }

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

    public static function enumerate() {
        $class = get_called_class();
        $ref = new ReflectionClass($class);
        $statics = $ref->getStaticProperties();
        foreach ($statics as $name => $value) {
            $ref->setStaticPropertyValue($name, new $class($value));
        }
    }
}

class DaysOfWeek extends Enum {
    public static $MONDAY = 0;
    public static $SUNDAY = 1;
    // etc.
}
DaysOfWeek::enumerate();

function isMonday(DaysOfWeek $d) {
    if ($d == DaysOfWeek::$MONDAY) {
        return true;
    } else {
        return false;
    }
}

$day = DaysOfWeek::$MONDAY;
echo (isMonday($day) ? "bummer it's monday" : "Yay! it's not monday");

如果您需要使用全局唯一的enum(即即使在不同enum之间比较元素时)并且易于使用，请随意使用以下代码。我还添加了一些我认为有用的方法。您可以在代码顶部的注释中找到示例。

<?php

/**
 * Class Enum
 * 
 * @author Christopher Fox <christopher.fox@gmx.de>
 *
 * @version 1.0
 *
 * This class provides the function of an enumeration.
 * The values of Enum elements are unique (even between different Enums)
 * as you would expect them to be.
 *
 * Constructing a new Enum:
 * ========================
 *
 * In the following example we construct an enum called "UserState"
 * with the elements "inactive", "active", "banned" and "deleted".
 * 
 * <code>
 * Enum::Create('UserState', 'inactive', 'active', 'banned', 'deleted');
 * </code>
 *
 * Using Enums:
 * ============
 *
 * The following example demonstrates how to compare two Enum elements
 *
 * <code>
 * var_dump(UserState::inactive == UserState::banned); // result: false
 * var_dump(UserState::active == UserState::active); // result: true
 * </code>
 *
 * Special Enum methods:
 * =====================
 *
 * Get the number of elements in an Enum:
 *
 * <code>
 * echo UserState::CountEntries(); // result: 4
 * </code>
 *
 * Get a list with all elements of the Enum:
 *
 * <code>
 * $allUserStates = UserState::GetEntries();
 * </code>
 *
 * Get a name of an element:
 *
 * <code>
 * echo UserState::GetName(UserState::deleted); // result: deleted
 * </code>
 *
 * Get an integer ID for an element (e.g. to store as a value in a database table):
 * This is simply the index of the element (beginning with 1).
 * Note that this ID is only unique for this Enum but now between different Enums.
 *
 * <code>
 * echo UserState::GetDatabaseID(UserState::active); // result: 2
 * </code>
 */
class Enum
{

    /**
     * @var Enum $instance The only instance of Enum (Singleton)
     */
    private static $instance;

    /**
     * @var array $enums    An array of all enums with Enum names as keys
     *          and arrays of element names as values
     */
    private $enums;

    /**
     * Constructs (the only) Enum instance
     */
    private function __construct()
    {
        $this->enums = array();
    }

    /**
     * Constructs a new enum
     *
     * @param string $name The class name for the enum
     * @param mixed $_ A list of strings to use as names for enum entries
     */
    public static function Create($name, $_)
    {
        // Create (the only) Enum instance if this hasn't happened yet
        if (self::$instance===null)
        {
            self::$instance = new Enum();
        }

        // Fetch the arguments of the function
        $args = func_get_args();
        // Exclude the "name" argument from the array of function arguments,
        // so only the enum element names remain in the array
        array_shift($args);
        self::$instance->add($name, $args);
    }

    /**
     * Creates an enumeration if this hasn't happened yet
     * 
     * @param string $name The class name for the enum
     * @param array $fields The names of the enum elements
     */
    private function add($name, $fields)
    {
        if (!array_key_exists($name, $this->enums))
        {
            $this->enums[$name] = array();

            // Generate the code of the class for this enumeration
            $classDeclaration =     "class " . $name . " {\n"
                        . "private static \$name = '" . $name . "';\n"
                        . $this->getClassConstants($name, $fields)
                        . $this->getFunctionGetEntries($name)
                        . $this->getFunctionCountEntries($name)
                        . $this->getFunctionGetDatabaseID()
                        . $this->getFunctionGetName()
                        . "}";

            // Create the class for this enumeration
            eval($classDeclaration);
        }
    }

    /**
     * Returns the code of the class constants
     * for an enumeration. These are the representations
     * of the elements.
     * 
     * @param string $name The class name for the enum
     * @param array $fields The names of the enum elements
     *
     * @return string The code of the class constants
     */
    private function getClassConstants($name, $fields)
    {
        $constants = '';

        foreach ($fields as $field)
        {
            // Create a unique ID for the Enum element
            // This ID is unique because class and variables
            // names can't contain a semicolon. Therefore we
            // can use the semicolon as a separator here.
            $uniqueID = $name . ";" . $field;
            $constants .=   "const " . $field . " = '". $uniqueID . "';\n";
            // Store the unique ID
            array_push($this->enums[$name], $uniqueID);
        }

        return $constants;
    }

    /**
     * Returns the code of the function "GetEntries()"
     * for an enumeration
     * 
     * @param string $name The class name for the enum
     *
     * @return string The code of the function "GetEntries()"
     */
    private function getFunctionGetEntries($name) 
    {
        $entryList = '';        

        // Put the unique element IDs in single quotes and
        // separate them with commas
        foreach ($this->enums[$name] as $key => $entry)
        {
            if ($key > 0) $entryList .= ',';
            $entryList .= "'" . $entry . "'";
        }

        return  "public static function GetEntries() { \n"
            . " return array(" . $entryList . ");\n"
            . "}\n";
    }

    /**
     * Returns the code of the function "CountEntries()"
     * for an enumeration
     * 
     * @param string $name The class name for the enum
     *
     * @return string The code of the function "CountEntries()"
     */
    private function getFunctionCountEntries($name) 
    {
        // This function will simply return a constant number (e.g. return 5;)
        return  "public static function CountEntries() { \n"
            . " return " . count($this->enums[$name]) . ";\n"
            . "}\n";
    }

    /**
     * Returns the code of the function "GetDatabaseID()"
     * for an enumeration
     * 
     * @return string The code of the function "GetDatabaseID()"
     */
    private function getFunctionGetDatabaseID()
    {
        // Check for the index of this element inside of the array
        // of elements and add +1
        return  "public static function GetDatabaseID(\$entry) { \n"
            . "\$key = array_search(\$entry, self::GetEntries());\n"
            . " return \$key + 1;\n"
            . "}\n";
    }

    /**
     * Returns the code of the function "GetName()"
     * for an enumeration
     *
     * @return string The code of the function "GetName()"
     */
    private function getFunctionGetName()
    {
        // Remove the class name from the unique ID 
        // and return this value (which is the element name)
        return  "public static function GetName(\$entry) { \n"
            . "return substr(\$entry, strlen(self::\$name) + 1 , strlen(\$entry));\n"
            . "}\n";
    }

}


?>

如果你想要类型安全和一堆与该类型匹配的常量，一种方法是为你的枚举创建一个抽象类，然后用一个锁定的构造函数扩展这个类，如下所示:

abstract class DaysOfWeekEnum{
    public function __construct(string $value){
        $this->value = $value; 
    }
    public function __toString(){
        return $this->value;
    }

}
class Monday extends DaysOfWeekEnum{
    public function __construct(){
        parent::__construct("Monday");
    }
}

class Tuesday extends DaysOfWeekEnum{
    public function __construct(){
        parent::__construct("Tuesday");
    }
}

然后你可以让你的方法获取DaysOfWeek的一个实例，并传递给它一个Monday、Tuesday等实例……唯一的缺点是每次你想使用你的枚举时都必须“更新”一个实例，但我发现这是值得的。

function printWeekDay(DaysOfWeek $day){
    echo "Today is $day.";
}

printWeekDay(new Monday());