Enumerations in PHP

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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 = "zambiatek"; 
    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) "zambiatek"
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 = "zambiatek"; 
    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) "zambiatek"
}
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 = "zambiatek"; 
    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) "zambiatek"
}
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.