PHP的Enum（枚举）的实现

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PHP其实有Enum类库的，需要安装perl扩展，所以不是php的标准扩展，因此代码的实现需要运行的php环境支持。

（1）扩展类库SplEnum类。该类的摘要如下：

SplEnum extends SplType {/* Constants */const NULL __default = null ;/* 方法 */public array getConstList ([ bool $include_default = false ] )/* 继承的方法 */SplType::__construct ([ mixed $initial_value [, bool $strict ]] )}

使用示例：

<?phpclass 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;}?>

　输出结果：

6Value not a const in enum Month

（2）自定义的Enum类库

摘自http://www.php4every1.com/scripts/php-enum/

<?php/** * Abstract class that enables creation of PHP enums. All you * have to do is extend this class and define some constants. * Enum is an object with value from on of those constants  * (or from on of superclass if any). There is also * __default constat that enables you creation of object * without passing enum value. * * @author Marijan Šuflaj <msufflaj32@Gmail.com&gt * @link http://php4every1.com */abstract class Enum {    /**     * Constant with default value for creating enum object     */    const __default = null;        private $value;        private $strict;        private static $constants = array();        /**     * Returns list of all defined constants in enum class.     * Constants value are enum values.     *     * @param bool $includeDefault If true, default value is included into return     * @return array Array with constant values     */    public function getConstList($includeDefault = false) {            $class = get_class($this);            if (!array_key_exists($class, self::$constants)) {            self::populateConstants();        }                return $includeDefault ? array_merge(self::$constants[__CLASS_], array(            "__default" => self::__default        )) : self::$constants[__CLASS_];    }        /**     * Creates new enum object. If child class overrides __construct(),      * it is required to call parent::__construct() in order for this     * class to work as expected.     *     * @param mixed $initialValue Any value that is exists in defined constants     * @param bool $strict If set to true, type and value must be equal     * @throws UnexpectedValueException If value is not valid enum value     */    public function __construct($initialValue = null, $strict = true) {            $class = get_class($this);            if (!array_key_exists($class, self::$constants)) {            self::populateConstants();        }                if ($initialValue === null) {            $initialValue = self::$constants[$class]["__default"];        }                $temp = self::$constants[$class];                if (!in_array($initialValue, $temp, $strict)) {            throw new UnexpectedValueException("Value is not in enum " . $class);        }                $this->value = $initialValue;        $this->strict = $strict;    }        private function populateConstants() {                $class = get_class($this);                $r = new ReflectionClass($class);        $constants = $r->getConstants();                self::$constants = array(            $class => $constants        );    }        /**     * Returns string representation of an enum. Defaults to      * value casted to string.     *     * @return string String representation of this enum's value     */    public function __toString() {        return (string) $this->value;    }        /**     * Checks if two enums are equal. Only value is checked, not class type also.     * If enum was created with $strict = true, then strict comparison applies      * here also.     *     * @return bool True if enums are equal     */    public function equals($object) {        if (!($object instanceof Enum)) {            return false;        }                return $this->strict ? ($this->value === $object->value)            : ($this->value == $object->value);    }}

使用示例如下：

class MyEnum extends Enum {    const HI = "Hi";    const BY = "By";    const NUMBER = 1;    const __default = self::BY;}var_dump(new MyEnum(MyEnum::HI));var_dump(new MyEnum(MyEnum::BY));//Use __defaultvar_dump(new MyEnum());try {    new MyEnum("I don't exist");} catch (UnexpectedValueException $e) {    var_dump($e->getMessage());}

输出结果如下：

object(MyEnum)#1 (2) {  ["value":"Enum":private]=>  string(2) "Hi"  ["strict":"Enum":private]=>  bool(true)}object(MyEnum)#1 (2) {  ["value":"Enum":private]=>  string(2) "By"  ["strict":"Enum":private]=>  bool(true)}object(MyEnum)#1 (2) {  ["value":"Enum":private]=>  string(2) "By"  ["strict":"Enum":private]=>  bool(true)}string(27) "Value is not in enum MyEnum"