枚举是一个整型常数的集合, 枚举在日常生活中很常见。
例如表示星期的SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY,
SATURDAY, 就是一个枚举。
枚举的说明与结构和联合相似, 其形式为:
enum 枚举名{（枚举值表）
立即学习“PHP免费学习笔记（深入）”；
标识符[=整型常数],
标识符[=整型常数],
...
标识符[=整型常数],
} 枚举变量;
如果枚举没有初始化, 即省掉"=整型常数"时, 则从第一个标识符开始, 依
次给标识符赋0, 1, 2, ...。但当枚举值表中的某个成员赋值后, 其后的成员按依次
加1的规则确定其值。
本文实例讲述了PHP中Enum(枚举)用法。分享给大家供大家参考，具体如下：
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 $strict ]] )
}使用示例：
getMessage() . PHP_EOL; } ?>
输出结果：
6 Value not a const in enum Month
（2）自定义的Enum类库
self::default
)) : self::$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" 
