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<?php namespace Core\Routing { interface Router { public function serve($uri); } class SimpleRouter implements Router { public function serve($uri) { echo 'Serving request: ', $uri, ' using ', __CLASS__; } } class FancyRouter implements Router { public function serve($uri) { echo 'Serving request: ', $uri, ' using ', __CLASS__; } } } namespace Core\Database { interface Connection { public function query($sql); } class MySQLConnection implements Connection { public function query($sql) { echo 'Querying: ', $sql, ' using ', __CLASS__; } } class MariaDBConnection implements Connection { public function query($sql) { echo 'Querying: ', $sql, ' using ', __CLASS__; } } } namespace Core { abstract class Application { protected static $instances = array(); private $properties = array(); public static function getInstance() { return isset(self::$instances[$className = get_called_class()]) ? self::$instances[$className] : self::$instances[$className] = new static(); } protected function __construct() { } public function __set($propertyName, $value) { $this->properties[$propertyName] = $value; } public function __get($propertyName) { return is_callable($this->properties[$propertyName]) ? $this->properties[$propertyName] = $this->properties[$propertyName]($this) : $this->properties[$propertyName]; } } abstract class WebApplication extends Application { protected $routerClassName = '\\Core\\Routing\\SimpleRouter'; // TODO: why not use constants here ??? maybe code should be allowed to modify dependencies at runtime ??? protected $databaseConnectionClassName = '\\Core\\Database\\MySQLConnection'; protected function __construct() { $this->router = function ($application) { //$routerClassName = $application->routerClassName; //return new $routerClassName(); return new $application->routerClassName(); }; $this->databaseConnection = function ($application) { $databaseConnectionClassName = $application->databaseConnectionClassName; return new $databaseConnectionClassName(); }; } } } namespace CompanyName { final class DiscussionsWebApplication extends \Core\WebApplication { protected $routerClassName = '\\Core\\Routing\\FancyRouter'; protected $databaseConnectionClassName = '\\Core\\Database\\MariaDBConnection'; } } namespace { CompanyName\DiscussionsWebApplication::getInstance()->router->serve('http://foo.bar/path/to/resource'); }