PHP traits, treat or threat?
Nick Belhomme January 28th, PHPBenelux Conference 2012, Belgium

Software Architect / Project Lead
Author of the Zend Framework 2.0 Cookbook International Conference Speaker Contributor to various Open Source Projects Freelance PHP Consultant

Market positions
http://w3techs.com/

Market positions
● Python 0.3%

Market positions ● Ruby 0.6%
● Python 0.3%

Market positions ● Perl 1.0%
● Ruby 0.6% ● Python 0.3%

Market positions ● ColdFusion 1.2%
● Perl 1.0% ● Ruby 0.6% ● Python 0.3%

Market positions ● Java 1.2%
● ColdFusion 1.2% ● Perl 1.0% ● Ruby 0.6% ● Python 0.3%

Market positions ● ASP.NET 21.6%
● Java 1.2% ● ColdFusion 1.2% ● Perl 1.0% ● Ruby 0.6% ● Python 0.3%

Market positions ● PHP 77.4%
● ASP.NET 21.6% ● Java 1.2% ● ColdFusion 1.2% ● Perl 1.0% ● Ruby 0.6% ● Python 0.3%

PHP Market Position, 11 Jan
2012 Used by high traffic sites Java ColdFusion Perl ASP.NET PHP Used by low traffic sites Used by fewer sites Used by many sites

PHP Version Adoption ● PHP
5 93.9% ● PHP 4 6.1% ● PHP 3 < 0.1% ● PHP 6 < 0.1%

PHP 5 usage ● Version
5.2 73.8% ● Version 5.3 20.2% ● Version 5.1 5.8% ● Version 5.0 0.2% ● Version 5.4 < 0.1%

Slow 5.3 Adoption? ● Shared
hosting ● Companies refrain from updating stable systems / distributions ● You

Adopt now ● More stability
● Security ● Better engine (ie garbage collection) ● New language features ● Cleaner code because of more elegant ways of solving problems

PHP 5.4 ● Array short
syntax (javascript notation) ● Array dereferencing ● Class access on instantiation ● Indirect method call by array variable ● Engine processes OO code faster ● <?= ● JSONSerializable interface ● ...

Traits

ZF Use Case ZF Code
base used is for illustration purposes only and do –not-- express future possible implementations. ZF2.0 is not yet released so giving ZF3.0 implementations illustrates only my own assumptions. PHP5.4 stable is not yet released so no real world projects are and should be running this version. Because of this no real best practices have been defined.

namespace ZendView; class TemplatePathStack implements
TemplateResolver { public function setOptions($options = array()) { if (!is_array($options) && !$options instanceof Traversable) { throw new ExceptionInvalidArgumentException( __METHOD__ . ' expects an array or Traversable' ); } foreach ($options as $key => $value) { $this->setOption($key, $value); } return $this; } public function setOption($key, $value) { switch (strtolower($key)) { case 'lfi_protection': $this->setLfiProtection($value); break; case 'script_paths': $this->addPaths($value); break; default: break; } } }

namespace ZendMvcRouter; class RouteBroker implements
Broker { public function setOptions($options) { if (!is_array($options) && !$options instanceof Traversable) { throw new ExceptionInvalidArgumentException(sprintf( 'Expected an array or Traversable; received "%s"', (is_object($options) ? get_class($options) : gettype($options)) )); } foreach ($options as $key => $value) { switch (strtolower($key)) { case 'class_loader': // handle this case Default: break;// ignore unknown options } } return $this; } }

Problem: Code Duplication if (!is_array($options)
&& !$options instanceof Traversable) { throw new ExceptionInvalidArgumentException(sprintf( 'Expected an array or Traversable; received "%s"', (is_object($options) ? get_class($options) : gettype($options)) )); } foreach ($options as $key => $value) { //handle each case } return $this;

Solution in PHP5.4? Multiple Inheritance
● Would provide the setOptions in all child classes needed ● Introduces the diamond problem

NOT an Option! A better
solution called Traits ● Would provide the setOptions in all classes that use the trait ● Eliminates the diamond problem

trait Options { public function
setOptions($options) { if (!is_array($options) && !$options instanceof Traversable) { throw new ExceptionInvalidArgumentException(sprintf( 'Expected an array or Traversable; received "%s"', (is_object($options) ? get_class($options) : gettype($options)) )); } foreach ($options as $key => $value) { $this->setOption($key, $value); } return $this; } }

namespace ZendView; class TemplatePathStack implements
TemplateResolver { use Options; public function setOption($key, $value) { switch (strtolower($key)) { case 'lfi_protection': $this->setLfiProtection($value); break; case 'script_paths': $this->addPaths($value); break; default: break; } } } $templateStack = new TemplatePathStack(); $templateStack->setOptions(['lfi_protection' => true]);

namespace ZendMvcRouter; class RouteBroker implements
Broker { use Options; public function setOption($key, $value) { switch (strtolower($key)) { case 'class_loader': // handle this case default: // ignore unknown options break; } } } $routeBroker = (new RouteBroker)->setOptions(['class_loader'=>'SomeLoader']);

You have just seen traits

Lets dive deeper get your
chest wet

namespace ZendLoader { use RuntimeException;
trait SplRegister { public function register() { spl_autoload_register(array($this, 'autoload')); } public function unregister() { spl_autoload_unregister(array($this, 'autoload')); } } class StandardAutoloader { use SplRegister; public function unregister() { throw new RuntimeException( 'you should not unregister the standard autoloader once registered' ); } } } namespace { $loader = new ZendLoaderStandardAutoloader(); $loader->register(); $loader->unregister(); // will throw the exception }

Precedence Order The precedence order
is that members from the current class override Trait methods.

namespace ZendLoader { use RuntimeException;
class StandardAutoloader { public function unregister() { throw new RuntimeException( 'you should not unregister the standard autoloader once registered' ); } } } namespace NbeZfLoader { use ZendLoader as ZendLoader; class StandardAutoloader extends ZendLoaderStandardAutoloader { use ZendLoaderSplRegister; } } namespace { $loader = new NbeZfLoaderStandardAutoloader(); $loader->register(); //will register (trait) $loader->unregister(); // will unregister (trait) }

Precedence Order An inherited member
from a base class is overridden by a member inserted by a Trait

Distil Methods!

namespace ZendLoader { use RuntimeException;
class StandardAutoloader { public function unregister() { throw new RuntimeException( 'you should not unregister the standard autoloader once registered' ); } } } namespace NbeZfLoader { use ZendLoader as ZendLoader; class StandardAutoloader extends ZendLoaderStandardAutoloader { use ZendLoaderSplRegister { ZendLoaderStandardAutoloader::unregister insteadof ZendLoaderSplRegister; } } } namespace { $loader = new NbeZfLoaderStandardAutoloader(); $loader->register(); //will register (trait) $loader->unregister(); // will throw RuntimeException (base class) }

insteadof Can be used to
say which method to use instead of the trait method.

Multiple Traits

namespace ZendFilter { trait Locale
{ protected $locale; public function getLocale() { return $this->locale; } public function setLocale($locale = null) { $this->locale = ZendLocale::findLocale($locale); return $this; } } trait WhiteSpace { protected $allowWhiteSpace; public function getAllowWhiteSpace() { return $this->allowWhiteSpace; } public function setAllowWhiteSpace($allowWhiteSpace) { $this->allowWhiteSpace = (boolean) $allowWhiteSpace; return $this; } } class Alpha extends AbstractFilter { use Locale, WhiteSpace; } }

Multiple Conflicting Traits The Diamond
Problem (Not yours or a girls best friend!)

namespace ZendFilter { trait Locale
{ protected $locale; public function getLocale() { return $this->locale; } public function setLocale($locale = null) { $this->locale = ZendLocale::findLocale($locale); return $this; } } trait SecondLocale { protected $locale; public function setLocale($locale = null) { if (is_string($locale)) { $locale = array($locale); } elseif ($locale instanceof Locale) { $locale = array($locale->toString()); } elseif (!is_array($locale)) { throw new ExceptionInvalidArgumentException( 'Locale has to be string, array or an instance of Zend_Locale' ); } foreach ($locale as $single) { if (!Locale::isLocale($single)) { throw new ExceptionInvalidArgumentException("Unknown locale '$single'"); } } $this->_locale = $locale; return $this; } } class Alpha { use Locale, SecondLocale; } } namespace { (new ZendFilterAlpha)->setLocale('nl_be'); }

Fatal error: Trait method getLocale
has not been applied, because there are collisions with other trait methods

Insteadof
to the rescue

namespace ZendFilter { trait Locale
{ protected $locale; public function getLocale() public function setLocale($locale = null) } trait SecondLocale { protected $locale; public function setLocale($locale = null) } class Alpha { use Locale, SecondLocale { SecondLocale::setLocale insteadof Locale; } } } namespace { $alpha = new ZendFilterAlpha(); $alpha->setLocale('nl_be'); }

WIN!

BUT Strict Standards: ZendFilterLocale and
ZendFilterSecondLocale define the same property ($locale) in the composition of ZendFilterAlpha. This might be incompatible, to improve maintainability consider using accessor methods in traits instead.

namespace ZendFilter { trait Locale
{ protected $locale = 'nl_BE'; public function getLocale() public function setLocale($locale = null) } trait SecondLocale { protected $locale = 'en_US'; public function setLocale($locale = null) } class Alpha { use Locale, SecondLocale { SecondLocale::setLocale insteadof Locale; } } } namespace { $alpha = new ZendFilterAlpha(); $alpha->setLocale('nl_BE'); }

Fatal error: ZendFilterLocale and ZendFilterSecondLocale
define the same property ($locale) in the composition of ZendFilterAlpha. However, the definition differs and is considered incompatible.

namespace ZendFilter { trait Locale
{ static public $locale = 'en_US'; public function getLocale() { return self::$locale; } public function setLocale($locale = null) { self::$locale = $locale; } } class Alpha { use Locale; public function get() { return self::$locale; } } } namespace { $alpha = new ZendFilterAlpha(); echo $alpha->getLocale(); // en_US echo $alpha->get(); // en_US $alpha->setLocale('nl_be'); echo $alpha->getLocale(); // nl_be echo $alpha->get(); // nl_be }

namespace ZendFilter { trait Locale
{ static public $locale = 'en_US'; public function getLocale() { return self::$locale; } public function setLocale($locale = null) { self::$locale = $locale; } } class Alpha { use Locale; public function get() { return self::$locale; } } class Beta { use Locale; } } namespace { $alpha = new ZendFilterAlpha(); echo $alpha->getLocale(); // en_US $alpha->setLocale('nl_be'); echo $alpha->getLocale(); // nl_be $beta = new ZendFilterBeta(); echo $beta->getLocale(); //en_US }

Aliassing, useful to replace the
parent:: construct

namespace ZendMvcController { Use ...
trait StdlibDispatch { public function dispatch(Request $request, Response $response = null) { $this->request = $request; if (!$response) { $response = new HttpResponse(); } $this->response = $response; ... if ($result->stopped()) { return $result->last(); } return $e->getResult(); } } abstract class ActionController implements Dispatchable, InjectApplicationEvent, LocatorAware { use StdlibDispatch; } abstract class RestfulController implementsDispatchable, InjectApplicationEvent, LocatorAware { use StdlibDispatch {StdlibDispatch::dispatch as dispatchTrait}; public function dispatch(Request $request, Response $response = null) { if (!$request instanceof HttpRequest) { throw new InvalidArgumentException('Expected an HTTP request'); } return $this->dispatchTrait($request, $response); } } }

Aliasing could potentially be a
refactoring nightmare

namespace ZendView; class TemplatePathStack implements
TemplateResolver { use Options { Options::setOptions as setConfig } } $templateStack = (new TemplatePathStack) ->setConfig(['lfi_protection' => true]); //$templateStack = (new TemplatePathStack) ->setOptions(['lfi_protection' => true]);

Visibility

namespace ZendView; class TemplatePathStack implements
TemplateResolver { use Options {Options::setOptions as protected} public function __construct($options = array()) { $this->setOptions($options); } } new TemplatePathStack(['lfi_protection' => true]);

Interface compliance

namespace ZendView; trait Options {
public function setOptions($options) { //set the options } } interface TemplateResolver { public function setConfig($options); } class TemplatePathStack implements TemplateResolver { use Options {Options::setOptions as setConfig;} } (new TemplatePathStack)->setConfig(['lfi_protection' => true]);

namespace ZendView; trait Options {
public function setOptions($options) { } } class TemplatePathStack { use Options { Options::setOptions as setConfig; } } $templateStack = (new TemplatePathStack) ->setConfig(['lfi_protection' => true]); var_dump($templateStack instanceof Options); // false

namespace ZendView; trait Options {
abstract public function setOptions($options); } class TemplatePathStack { use Options; public function setOptions($options) { echo 'implementation enforced by trait'; } } $templateStack = (new TemplatePathStack) ->setOptions(['lfi_protection' => true]); var_dump($templateStack instanceof Options); // false

namespace ZendView; trait Options {
abstract public function setOptions($options); } class TemplatePathStack { use Options {Options::setOptions as setConfig;} public function setConfig($options) { echo 'implementation enforced by trait'; } } // Fatal error: Class ZendViewTemplatePathStack contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (ZendViewTemplatePathStack::setOptions)

Magic Constants <?php trait Id
{ public function getClass() { echo __CLASS__; } public function getTrait() { echo __TRAIT__; } } class Foo { use Id; } (new Foo)->getClass(); //Foo (new Foo)->getTrait(); //Id

Autoloading <?php namespace NbeZfLoader{ class
foo { use Id; } } namespace { function __autoload($class) { var_dump($class); die(); } } // string(15) "NbeZfLoaderId"

Good things about traits ●
Removes code duplication ● Helps keeping your code cleaner ● Maintainability ● Aliassing works for interfaces ● Property handling ● Easy Autoloading

Bad things about traits ●
Adds code complexity / understandability with the insteadof operator. ● Duck typing ● Aliassing Fails for Abstract Classes ● Property handling

Benchmarks 5.3 vs 5.4 ●
ZF project: http://nickbelhomme.com ● Benchmark / Profiling tool: xhprof ● How: 2 VirtualBox Machines - debian clones, with only PHP upgrade (5.4.0RC3)

5.3.3 ● Total Incl. Wall
Time (microsec): 674,842 ms ● Total Incl. CPU (microsecs): 672,042 ms ● Total Incl. MemUse (bytes): 13,827,864 bytes ● Total Incl. PeakMemUse (bytes): 13,865,976 bytes ● Number of Function Calls: 14,524

5.4.0RC3 Total Incl. Wall Time
(microsec): 166,813 ms ● Total Incl. CPU (microsecs): 168,011 ms ● Total Incl. MemUse (bytes):7,969,928 bytes ● Total Incl. PeakMemUse (bytes):8,015,944 bytes ● Number of Function Calls: 14,520

Who runs PHP5.4 today for
testing?

YOU WIN
6

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The End! THANK YOU Please
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Flickr Photo Credits ● Helico
● donkeyhotey ● jannem ● Thomas.constantin ● SJ photography ● davidagalvan ● stev.ie ● Mosman Council ● DeaPeaJay