php - 在 PHP5 中创建单例设计模式

Question

如何使用 PHP5 类创建单例类？

Answer 1

/**
 * Singleton class
 *
 */
final class UserFactory
{
    private static $inst = null;

    // Prevent cloning and de-serializing
    private function __clone(){}
    private function __wakeup(){}


    /**
     * Call this method to get singleton
     *
     * @return UserFactory
     */
    public static function Instance()
    {
        if ($inst === null) {
            $inst = new UserFactory();
        }
        return $inst;
    }
    
    /**
     * Private ctor so nobody else can instantiate it
     *
     */
    private function __construct()
    {
        
    }
}

使用方法:

$fact = UserFactory::Instance();
$fact2 = UserFactory::Instance();

$fact == $fact2;

但是:

$fact = new UserFactory()

引发错误。

见 http://php.net/manual/en/language.variables.scope.php#language.variables.scope.static了解静态变量范围以及设置 static $inst = null; 的原因。