The Singleton pattern possesses two general features:
The default class constructor cannot be called. Instead, it will be called through a designated class maintainer method that ensures only one instantiation is available at any given time.
A static class member that holds a reference to the existing class resource identifier.
Let's build a PHP class using the Singleton development pattern. Suppose that you're creating a Web-based action game. Of course, there can be one and only one hero, and therefore we need to ensure that only one exists at any given time. Sounds like a perfect reason to use the Singleton pattern! In Listing 1-1, I create a singleton class titled Hero(), and show you how even multiple instantiations yield the same object.
Listing 1-1. A PHP-based singleton pattern implementation
<?php
class Hero {
private static $exists = NULL;
private $name = "Superhero";
private function __construct() {
// No implementation.
}
static function introduce() {
if (self::$exists === NULL) {
self::$exists = new Hero();
}
return self::$exists;
}
function setName($name) {
$this->name = $name;
}
function getName() {
return $this->name;
}
} #end class Hero
$hero = Hero::introduce();
$hero->setName("Lance");
var_dump($hero);
echo "The hero's name is: ".$hero->getName()."<br />";
$hero2 = Hero::introduce();
var_dump($hero2);
echo "The hero's name is: ".$hero2->getName()."<br />";
$hero2->setName("Bruce");
echo "The hero's name is: ".$hero->getName()."<br />";
echo "The hero's name is: ".$hero2->getName()."<br />";
?>
Executing this example yields:
object(Hero)#1 (1) { } The hero's name is: Lance.
object(Hero)#1 (1) { } The hero's name is: Lance
The hero's name is: Bruce
The hero's name is: Bruce
As you can see by the above output, we're only dealing with one instance of the class throughout the entire example.
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