Enumerations in PHP

Enumeration (or enum) is mainly used to assign names to integral constants, the names make a program easy to read and maintain. In PHP, enumeration datatypes can be implemented using and extending abstract classes.

Approach 1: Using simple abstract class to for data member encapsulation.

Example:

<?php
// PHP program to show use of enumerations

// Encapsulating constants
abstract class gfg {
    const dummy_string = "geeksforgeeks";
    const dummy_int    = 1;
    const dummy_array  = array('a' => 1, 'b' => 2);
}

$a = gfg::dummy_string;
$b = gfg::dummy_int;
$c = gfg::dummy_array;

var_dump($a);
var_dump($b);
var_dump($c);

?>

Output:

string(13) "geeksforgeeks"
int(1)
array(2) {
  ["a"]=>
  int(1)
  ["b"]=>
  int(2)
}

Approach 2: Extend an abstract class acting as an enumeration container for encapsulating constants.

Example:

<?php
// PHP program to show use of enumerations

// Base enumeration class
abstract class enum {

    // Enumeration constructor
    final public function __construct($value) {
        $this->value = $value;
    }

    // String representation
    final public function __toString() {
        return $this->value;
    }
}

// Encapsulating enumerated constants
class gfg extends enum {
    const dummy_string = "geeksforgeeks";
    const dummy_int    = 1;
    const dummy_array  = array('a' => 1, 'b' => 2);
}

$a = new gfg(gfg::dummy_string);
$b = new gfg(gfg::dummy_int);
$c = new gfg(gfg::dummy_array);

var_dump($a);
var_dump($b);
var_dump($c);

?>

Output:

object(gfg)#1 (1) {
  ["value"]=>
  string(13) "geeksforgeeks"
}
object(gfg)#2 (1) {
  ["value"]=>
  int(1)
}
object(gfg)#3 (1) {
  ["value"]=>
  array(2) {
    ["a"]=>
    int(1)
    ["b"]=>
    int(2)
  }
}

Approach 3: Enumeration mentioned in the previous approach can be specialized by addition of validity checks and exception handling for more flexible usage of enumeration datatype.

Example:

<?php
// PHP program to show use of enumerations

// Base enumeration class
abstract class enum {

    // Enumeration constructor
    final public function __construct($value) {
        try {
            $c = new ReflectionClass($this);

            // Content validation
            if(!in_array($value, $c->getConstants())) {
                try {
                    throw new
                    Exception("IllegalArgumentException");
                }
                catch (Exception $k) {
                    echo $k->getMessage();
                }
            }
            $this->value = $value;
        }
        catch (Exception $k){
            echo $k->getMessage();
        }
    }

    // String representation
    final public function __toString() {
        return $this->value;
    }
}

// Encapsulating enumerated constants
class gfg extends enum {
    const dummy_string = "geeksforgeeks";
    const dummy_int    = 1;
    const dummy_array  = array('a' => 1, 'b' => 2);
}

$a = new gfg(gfg::dummy_string);
$b = new gfg(gfg::dummy_int);
$c = new gfg(gfg::dummy_array);
$d = new gfg(3.14);

var_dump($a);
var_dump($b);
var_dump($c);
var_dump($d);
?>

Output:

IllegalArgumentExceptionobject(gfg)#1 (1) {
  ["value"]=>
  string(13) "geeksforgeeks"
}
object(gfg)#2 (1) {
  ["value"]=>
  int(1)
}
object(gfg)#3 (1) {
  ["value"]=>
  array(2) {
    ["a"]=>
    int(1)
    ["b"]=>
    int(2)
  }
}
object(gfg)#4 (1) {
  ["value"]=>
  float(3.14)
}

Note: PHP has SplEnum class which can be used for enumerations, though the implementation is not available in all stable versions of PHP.