how to import multiple namespaces properly - php

Question

I am very new to PHP namespaces and I have a question:
If we import multiple namespaces with the 'use' command, shouldn't we run into issues?
I have been reading through this post http://www.sitepoint.com/php-namespaces-import-alias-resolution/, and in the section about Namespace Importing, it says that you still need to have a qualified prefix next to a function (ie: Lib2), but when looking at some Symfony 2 example files, I don't see that happening.
How is namespacing solving (in the example file below) solving name conflicts?
namespace Acme\DemoBundle\Controller;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Symfony\Component\HttpFoundation\Request;
use Acme\DemoBundle\Form\ContactType;
// these import the "#Route" and "#Template" annotations
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Template;
class DemoController extends Controller
{
/**
* #Route("/", name="_demo")
* #Template()
*/
public function indexAction()
{
return array();
}
/**
* #Route("/hello/{name}", name="_demo_hello")
* #Template()
*/
public function helloAction($name)
{
return array('name' => $name);
}
/**
* #Route("/contact", name="_demo_contact")
* #Template()
*/
public function contactAction(Request $request)
{
$form = $this->createForm(new ContactType());
$form->handleRequest($request);
if ($form->isValid()) {
$mailer = $this->get('mailer');
// .. setup a message and send it
// http://symfony.com/doc/current/cookbook/email.html
$request->getSession()->getFlashBag()->set('notice', 'Message sent!');
return new RedirectResponse($this->generateUrl('_demo'));
}
return array('form' => $form->createView());
}
}

Answer 1

I think the misunderstanding comes from the post's filenames. keep in mind:
DefaultController.php with namespace Acme/AcmeBundle/Controller/ will be included with use Acme/AcmeBundle/Controller/DefaultController
DefaultController2.php with namespace Acme/AcmeBundle/Controller2/ will be included with use Acme/AcmeBundle/Controller2/DefaultController2
To have a conflict you'd need to include two files named DefaultController.php
DefaultController.php with namespace Acme/AcmeBundle/Controller
DefaultController.php with namespace Acme/AcmeBundle/Controller2
And would then need an alias as pointed out by Kevin
DefaultController.php with namespace Acme/AcmeBundle/Controller
=> use Acme/AcmeBundle/Controller/DefaultController
DefaultController.php with namespace Acme/AcmeBundle/Controller2
=> use Acme/AcmeBundle/Controller2/DefaultController as DefaultController2

Answer 2

Maybe the best way to explain this is to work backwards from the namespace resolution.
Say you have a line like the following:
$newFoo = new Foo();
PHP will look through the current symbol table for the class Foo. That symbol table includes the current namespace and any imported (use) namespaces (as well as built-in PHP symbols).
For example, say class Foo is declared in Foo.php:
<?php //Baz/Foo.php
namespace Baz\Foo;
class Foo{}
If you were working in Bar.php, you could reference the following:
<?php //Baz/Bar.php
namespace Baz\Bar;
use Baz\Foo;
//The following lines are equivalent
$newFoo = new Foo\Foo(); //Local namespace
$newFoo = new \Baz\Foo\Foo(); //Fully qualified namespace
You could also reference the Foo class directly in your use, rather than referencing the Foo namespace.
<?php //Baz/Bar.php
namespace Baz\Bar;
use Baz\Foo\Foo;
//The following lines are equivalent
$newFoo = new Foo(); //Local namespace
//$newFoo = new Foo\Foo(); //This will fail, as the symbol Foo is a class, not a namespace
$newFoo = new \Baz\Foo\Foo(); //Fully qualified namespace still works.
If you wanted to reference both the Namespace and the Class Foo directly, you'd need to resolve the conflict with an Alias.
<?php //Baz/Bar.php
namespace Baz\Bar;
use Baz\Foo;
use Baz\Foo\Foo as FooClass;
//The following lines are equivalent
$newFoo = new FooClass(); //Notice the new aliased symbol.
$newFoo = new Foo\Foo(); //This works now.
$newFoo = new \Baz\Foo\Foo(); //Fully qualified namespace still works.
//$newFoo = new \Baz\Foo\FooClass(); //This will fail, aliases don't work for fully qualified names.
Also, say, in addition to your Baz/Foo.php file, you have a Bar/Foo.php file as such:
<?php //Bar/Foo.php
namespace Bar\Foo;
class Foo{}
If you wanted to reference both namespaces locally, you'll need aliases to resolve the name conflict:
<?php //Baz/Bar.php
namespace Baz\Bar;
use Baz\Foo as Foo1;
use Baz\Foo\Foo as Foo1Class;
use Bar\Foo as Foo2;
use Bar\Foo\Foo as Foo2Class;
//The following lines are equivalent, referencing Baz\Foo\Foo
$newBazFoo = new Foo1Class(); //Object alias.
$newBazFoo = new Foo1\Foo(); //Namespace alias.
$newBazFoo = new \Baz\Foo\Foo(); //Fully qualified namespaces don't need any aliases.
//The following lines are equivalent, referencing Bar\Foo\Foo
$newBarFoo = new Foo2Class(); //Object alias.
$newBarFoo = new Foo2\Foo(); //Namespace alias.
$newBarFoo = new \Bar\Foo\Foo(); //Fully qualified namespaces don't need any aliases.
In addition to importing the Namespace with the use statement, you will also need to include the file containing that namespace. This can be done manually with require_once(), but is normally handled automatically by an autoloader.
See Symfony Class Loader for more details.
Hope that helps.