Enumerations on PHP

Question

I know that PHP doesn't yet have native Enumerations. But I have become accustomed to them from the Java world. I would love to use enums as a way to give predefined values which IDEs' auto-completion features could understand.

Constants do the trick, but there's the namespace collision problem and (or actually because) they're global. Arrays don't have the namespace problem, but they're too vague, they can be overwritten at runtime and IDEs rarely know how to autofill their keys without additional static analysis annotations or attributes.

Are there any solutions/workarounds you commonly use? Does anyone recall whether the PHP guys have had any thoughts or decisions around enumerations?

Answer 1

There is a native extension, too. The SplEnum

SplEnum gives the ability to emulate and create enumeration objects natively in PHP.

http://www.php.net/manual/en/class.splenum.php

Attention:

https://www.php.net/manual/en/spl-types.installation.php

The PECL extension is not bundled with PHP.

A DLL for this PECL extension is currently unavailable.

Answer 2

Depending upon use case, I would normally use something simple like the following:

abstract class DaysOfWeek {     const Sunday = 0;     const Monday = 1;     // etc. }  $today = DaysOfWeek::Sunday; 

However, other use cases may require more validation of constants and values. Based on the comments below about reflection, and a few other notes, here's an expanded example which may better serve a much wider range of cases:

abstract class BasicEnum {     private static $constCacheArray = NULL;      private static function getConstants() {         if (self::$constCacheArray == NULL) {             self::$constCacheArray = [];         }         $calledClass = get_called_class();         if (!array_key_exists($calledClass, self::$constCacheArray)) {             $reflect = new ReflectionClass($calledClass);             self::$constCacheArray[$calledClass] = $reflect->getConstants();         }         return self::$constCacheArray[$calledClass];     }      public static function isValidName($name, $strict = false) {         $constants = self::getConstants();          if ($strict) {             return array_key_exists($name, $constants);         }          $keys = array_map('strtolower', array_keys($constants));         return in_array(strtolower($name), $keys);     }      public static function isValidValue($value, $strict = true) {         $values = array_values(self::getConstants());         return in_array($value, $values, $strict);     } } 

By creating a simple enum class that extends BasicEnum, you now have the ability to use methods thusly for simple input validation:

abstract class DaysOfWeek extends BasicEnum {     const Sunday = 0;     const Monday = 1;     const Tuesday = 2;     const Wednesday = 3;     const Thursday = 4;     const Friday = 5;     const Saturday = 6; }  DaysOfWeek::isValidName('Humpday');                  // false DaysOfWeek::isValidName('Monday');                   // true DaysOfWeek::isValidName('monday');                   // true DaysOfWeek::isValidName('monday', $strict = true);   // false DaysOfWeek::isValidName(0);                          // false  DaysOfWeek::isValidValue(0);                         // true DaysOfWeek::isValidValue(5);                         // true DaysOfWeek::isValidValue(7);                         // false DaysOfWeek::isValidValue('Friday');                  // false 

As a side note, any time I use reflection at least once on a static/const class where the data won't change (such as in an enum), I cache the results of those reflection calls, since using fresh reflection objects each time will eventually have a noticeable performance impact (Stored in an assocciative array for multiple enums).

Now that most people have finally upgraded to at least 5.3, and SplEnum is available, that is certainly a viable option as well--as long as you don't mind the traditionally unintuitive notion of having actual enum instantiations throughout your codebase. In the above example, BasicEnum and DaysOfWeek cannot be instantiated at all, nor should they be.