PHP的Enum（枚举）的实现

cto67

　　转载请保留原文地址：http://www.iyunv.com/zsxfbj/p/php_enum.html
　　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：



<?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;
}
?>

　　输出结果：



6
Value 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 &Scaron;uflaj <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 __default
var_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"