PHP中Enum(枚举)用法实例详解

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：

    <?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

    <?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>
     * @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"

希望本文所述对大家PHP程序设计有所帮助。