Tips on using Enum in PHP

This article mainly introduces the usage skills of Enum in PHP. Interested friends can refer to it. I hope it will be helpful to everyone.

PHP actually has the Enum class library, which requires the installation of the perl extension, so it is not a standard extension of PHP, so the implementation of the code requires the support of the running PHP environment.

(1) Extend the class library SplEnum class. The summary of this class is as follows:

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 ]] )
}

Usage example:

<?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;
}
?>

Output result:

6
Value not a const in enum Month

(2) Customized Enum class library

<?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&#39;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);
  }
}

Usage An example is as follows:

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());
}

The output result is as follows:

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"

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