Dealing With
Dependencies
Stefan Priebsch confoo 2010
thePHP.cc Montreal

Stefan Priebsch
Co-Founder and Principal Consultant

Premium PHP Consulting & Training. Worldwide.
Sebastian Arne Stefan
Bergmann Blankerts Priebsch

Dependency

„Dependency is the
degree to which each
program module relies
on each one of the
other modules.“

Module
Module Module
Module

Module
Module Module
Module

global $config;
Globals
Superglobals
$username = $_POST['username'];
$password = $_POST['password'];
if ($config['auth_source'] == 'ldap') {
require_once APP_PATH . DS . 'inc/ldap.php';
$ldap = new LdapAuthentication(); Objects
$result = $ldap->authenticate($username, $password);
} else { Constants
$passwords = file(APP_PATH . DS . DATA_DIR . DS . 'passwd');
$result = isset($passwords[$username]) &&
$passwords[$username] == $password;
}
if ($result) {
Classes
Session::set('username', $username);
}
return $result;

Your Code
G C Function Function
S G F Function Function
G C S F G G S

Code
Dependencies

External
Dependencies

External Dependencies
● Files
● Databases
● Services
● External Programs

Constants

class NumberCruncher
{
public function load(...)
{
$file = BASEPATH . '/name.php';
…
}
}

class NumberCruncher
{
protected $basePath = BASEPATH;
public function load(...)
{
$file = $this->basePath . '/name.php';
...
}
}

class NumberCruncher
{
protected $basePath = BASEPATH;
public function setBasePath($basePath)
{
$this->basePath = $basePath;
}
public function load(...)
{
$file = $this->basePath. '/name.php';
...
}
}

class NumberCruncher
{
protected $basePath;
public function setBasePath($basePath)
{
$this->basePath = $basePath;
}
public function load(...)
{
$file = $this->basePath. '/name.php';
...
}
}

class NumberCruncher
{
protected $basePath;
public function __construct($basePath)
{
$this->basePath = $basePath;
}
public function load(...)
{
$file = $this->basePath. '/name.php';
...
}
}

class NumberCruncher
{
public function load($file, ...)
{
…
}
}

Globals

class NumberCruncher
{
public function calculate(...)
{
global $log;
…
}
}

class NumberCruncher
{
public function calculate(...)
{
$log = $GLOBALS['log'];
...
}
}

class NumberCruncher
{
public function calculate($log, ...)
{
...
}
}

class NumberCruncher
{
protected $log;
public function __construct($log)
{
$this->log = $log;
}
public function calculate(...)
{
...
}
}

Superglobals

class Controller
{
public function execute(...)
{
…
$username = $_POST['username'];
$password = $_POST['password'];
...
}
}

class Request
{
protected $get;
protected $post;
...
public function __construct(array $get, array $post, ...)
{
$this->get = $get;
$this->post = $post;
...
}
...
}

class Request
{
...
public function get($key)
public function post($key)
public function cookie($name)
public function server($key)
...
}

$request = new Request($_GET, $_POST, ...);
Dependency
…
$controller = new Controller($request); Creation
…
$controller->execute();
Workflow
...

bootstrap.php
$request = new Request($_GET, $_POST, ...);
ControllerFactory.php
$controller = new Controller($request);
FrontController.php
$controller->execute();

Dependency
Injection

„A technique for
supplying an external
dependency to a
software component.“

Separate
Object Creation
from Workflow

Objects

class NumberCruncher
{
protected $log;
public function __construct($log)
{
$this->log = $log;
}
public function calculate(...)
{
…
}
}

$logger = new Logger();
…
$nc = new NumberCruncher($logger);
$nc->calculate();

class NumberCruncher
{
protected $log;
public function __construct($log)
{
$this->log = $log;
}
public function calculate(...)
{
…
$this->log->log(...);
...
}
}

class NumberCruncher
{
protected $log;
public function __construct(Logger $log)
{
$this->log = $log;
}
public function calculate(...)
{
…
$this->log->log(...);
...
}
}

Explicit
Dependency

class NumberCruncher
{
protected $log;
public function __construct(Logger $log = null)
{
if ($log === null) {
$log = new Logger();
}
$this->log = $log;
}
public function calculate(...)
{
…
$this->log->log(...);
...
}
}

Classes

class NumberCruncher
{
public function calculate(...)
{
…
Logger::log(...);
...
}
}

Implicit
Dependency

Just Don't

Data Loading
Revisited

class NumberCruncher
{
public function load($file, ...)
{
… load $file ...
}
}

class NumberCruncher
{
protected $dataLoader;
public function __construct(DataLoader $loader)
{
$this->dataLoader = $loader;
}
public function load(...)
{
…
$data = $this->dataLoader->load();
...
}
}

Interfaces

class NumberCruncher
{
protected $dataLoader;
public function __construct(DataLoaderInterface $loader)
{
$this->dataLoader = $loader;
}
public function load(...)
{
…
$data = $this->dataLoader->load();
...
}
}

interface DataLoaderInterface
{
public function load();
}

class DataLoader implements DataLoaderInterface
{
protected $file;
public function __construct($file)
{
$this->file = $file;
}
public function load()
{
...
}
}

(Unit) Testing

Mock Objects

„Mock objects are
simulated objects that
mimic the behavior of
real objects in
controlled ways.“

class MockDataLoader implements DataLoaderInterface
{
public function load()
{
return array(
'0' => array(...),
'1' => array(...),
...
);
}
}

PHPUnit

class NumberCruncherTest extends PHPUnit_Framework_TestCase
{
public function testNumberCrunching
{
$data = array(
'0' => array(...),
'1' => array(...),
...
);
$loader = $this->getMock('DataLoaderInterface')
->expects($this->once())
->method('load')
->will($this->returnValue($data));
$cruncher = new DataCruncher($loader);
...
}
}

Thank You

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