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

我在github上找到了这个库,我认为它提供了一个非常不错的答案。

PHP枚举实现灵感来自脾

你可以输入:function setAction(Action $ Action) { 你可以用方法丰富枚举(例如format, parse,…) 您可以扩展枚举以添加新值(将枚举设置为final以防止出现这种情况) 您可以得到所有可能值的列表(见下面)

宣言

<?php
use MyCLabs\Enum\Enum;

/**
 * Action enum
 */
class Action extends Enum
{
    const VIEW = 'view';
    const EDIT = 'edit';
}

使用

<?php
$action = new Action(Action::VIEW);

// or
$action = Action::VIEW();

类型提示枚举值:

<?php
function setAction(Action $action) {
    // ...
}

其他回答

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());

对于简单的枚举,我使用如下结构。通常,您可以将它们用于switch语句。

<?php 
  define("OPTION_1", "1");
  define("OPTION_2", OPTION_1 + 1);
  define("OPTION_3", OPTION_2 + 1);

  // Some function...
   switch($Val){
    case OPTION_1:{ Perform_1();}break;
    case OPTION_2:{ Perform_2();}break;
    ...
  }
?>

它不像c++中的本地枚举那样方便,但如果你以后想在两者之间添加一个选项,它似乎可以工作,并且需要更少的维护。

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)

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。

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";
    }

}


?>