PHP Objects, Patterns, and Practice, Third Edition

CHAPTER 12 ■ ENTERPRISE PATTERNS

241

You may wonder why this code takes it on trust that the Command class it locates does not require

parameters:

if ( $cmd_class->isSubClassOf( self::$base_cmd ) ) {

return $cmd_class->newInstance();

}

The answer to this lies in the signature of the Command class itself.

Namespace woo\command;

//...

abstract class Command {

final function __construct() { }

function execute( \woo\controller\Request $request ) {

$this->doExecute( $request );

}

abstract function doExecute( \woo\controller\Request $request );

}

By declaring the constructor method final, I make it impossible for a child class to override it. No

Command class, therefore, will ever require arguments to its constructor.

Remember that you ...