PHP: Hypertext Preprocessor

Traits

PHP implémente une manière pour réutiliser du code appelée Traits.

Les traits sont un mécanisme de réutilisation de code dans un langage à héritage simple tel que PHP. Un trait tente de réduire certaines limites de l'héritage simple, en autorisant le développeur à réutiliser un certain nombre de méthodes dans des classes indépendantes. La sémantique entre les classes et les traits réduit la complexité et évite les problèmes typiques de l'héritage multiple et des Mixins.

Un trait est semblable à une classe, mais il ne sert qu'à grouper des fonctionnalités d'une manière intéressante. Il n'est pas possible d'instancier un Trait en lui-même. C'est un ajout à l'héritage traditionnel, qui autorise la composition horizontale de comportements, c'est-à-dire l'utilisation de méthodes de classe sans besoin d'héritage.

Exemple #1 Exemple d'utilisation de Trait

<?php
trait ezcReflectionReturnInfo {
    function getReturnType() { /*1*/ }
    function getReturnDescription() { /*2*/ }
}

class ezcReflectionMethod extends ReflectionMethod {
    use ezcReflectionReturnInfo;
    /* ... */
}

class ezcReflectionFunction extends ReflectionFunction {
    use ezcReflectionReturnInfo;
    /* ... */
}
?>

Précédence

Une méthode héritée depuis une classe mère est écrasée par une méthode issue d'un Trait. L'ordre de précédence fait en sorte que les méthodes de la classe courante écrasent les méthodes issues d'un Trait, elles-mêmes surchargeant les méthodes héritées.

Exemple #2 Exemple avec l'ordre de précédence

Une méthode héritée depuis la classe de base est écrasée par celle provenant du Trait. Ce n'est pas le cas des méthodes réelles, écrites dans la classe de base.

<?php
class Base {
    public function sayHello() {
        echo 'Hello ';
    }
}

trait SayWorld {
    public function sayHello() {
        parent::sayHello();
        echo 'World!';
    }
}

class MyHelloWorld extends Base {
    use SayWorld;
}

$o = new MyHelloWorld();
$o->sayHello();
?>

L'exemple ci-dessus va afficher :

Hello World!

Exemple #3 Autre exemple d'ordre de précédence

<?php
trait HelloWorld {
    public function sayHello() {
        echo 'Hello World!';
    }
}

class TheWorldIsNotEnough {
    use HelloWorld;
    public function sayHello() {
        echo 'Hello Universe!';
    }
}

$o = new TheWorldIsNotEnough();
$o->sayHello();
?>

L'exemple ci-dessus va afficher :

Hello Universe!

Multiples Traits

Une classe peut utiliser de multiples Traits en les déclarant avec le mot-clé use, séparés par des virgules.

Exemple #4 Utilisation de plusieurs Traits

<?php
trait Hello {
    public function sayHello() {
        echo 'Hello ';
    }
}

trait World {
    public function sayWorld() {
        echo 'World';
    }
}

class MyHelloWorld {
    use Hello, World;
    public function sayExclamationMark() {
        echo '!';
    }
}

$o = new MyHelloWorld();
$o->sayHello();
$o->sayWorld();
$o->sayExclamationMark();
?>

L'exemple ci-dessus va afficher :

Hello World!

Résolution des conflits

Si deux Traits insèrent une méthode avec le même nom, une erreur fatale est levée si le conflit n'est pas explicitement résolu.

Pour résoudre un conflit de nommage entre des Traits utilisés dans la même classe, il faut utiliser l'opérateur insteadof pour choisir une des méthodes en conflit.

Puisque ce principe ne permet que d'exclure des méthodes, l'opérateur as peut être utilisé pour permettre l'inclusion d'une des méthodes conflictuelles sous un autre nom. Notez que l'opérateur as ne renomme pas la méthode et n'affecte pas d'autres méthodes non plus.

Exemple #5 Résolution des conflits

Dans cet exemple, la classe Talker utilise les traits A et B. Comme A et B ont des méthodes conflictuelles, on indique que l'on souhaite utiliser la variante de smallTalk depuis le trait B, et la variante de bigTalk depuis le trait A.

La classe Aliased_Talker utilise l'opérateur as pour être capable d'utiliser l'implémentation bigTalk de B sous un alias supplémentaire talk.

<?php
trait A {
    public function smallTalk() {
        echo 'a';
    }
    public function bigTalk() {
        echo 'A';
    }
}

trait B {
    public function smallTalk() {
        echo 'b';
    }
    public function bigTalk() {
        echo 'B';
    }
}

class Talker {
    use A, B {
        B::smallTalk insteadof A;
        A::bigTalk insteadof B;
    }
}

class Aliased_Talker {
    use A, B {
        B::smallTalk insteadof A;
        A::bigTalk insteadof B;
        B::bigTalk as talk;
    }
}
?>

Changer la visibilité des méthodes

En utilisant la syntaxe as, vous pouvez aussi ajuster la visibilité de la méthode dans la classe qui l'utilise.

Exemple #6 Changer la visibilité des méthodes

<?php
trait HelloWorld {
    public function sayHello() {
        echo 'Hello World!';
    }
}

// Modification de la visibilité de la méthode sayHello
class MyClass1 {
    use HelloWorld { sayHello as protected; }
}

// Utilisation d'un alias lors de la modification de la visibilité
// La visibilité de la méthode sayHello n'est pas modifiée
class MyClass2 {
    use HelloWorld { sayHello as private myPrivateHello; }
}
?>

Traits Composés depuis d'autres Traits

Tout comme les classes peuvent utiliser des traits, d'autres traits le peuvent aussi. Un trait peut donc utiliser d'autres traits et hériter de tout ou d'une partie de ceux-ci.

Exemple #7 Traits Composés depuis d'autres Traits

<?php
trait Hello {
    public function sayHello() {
        echo 'Hello ';
    }
}

trait World {
    public function sayWorld() {
        echo 'World!';
    }
}

trait HelloWorld {
    use Hello, World;
}

class MyHelloWorld {
    use HelloWorld;
}

$o = new MyHelloWorld();
$o->sayHello();
$o->sayWorld();
?>

L'exemple ci-dessus va afficher :

Hello World!

Méthodes abstraites dans les Traits

Les traits supportent l'utilisation de méthodes abstraites afin d'imposer des contraintes aux classes sous-jacentes. Les méthodes publiques, protégées, et privées sont supportées. Antérieur à PHP 8.0.0, seule les méthodes publiques et protégées abstraire étaient supportées.

Attention

À partir de PHP 8.0.0, la signature d'une méthode concrète doit suivre les règles de compatibilité des signatures. Auparavant, sa signature pouvait être différente.

Exemple #8 Obligations requises par les méthodes abstraites

<?php
trait Hello {
    public function sayHelloWorld() {
        echo 'Hello'.$this->getWorld();
    }
    abstract public function getWorld();
}

class MyHelloWorld {
    private $world;
    use Hello;
    public function getWorld() {
        return $this->world;
    }
    public function setWorld($val) {
        $this->world = $val;
    }
}
?>

Attributs statiques dans les Traits

Les traits peuvent définir des variables statiques, méthodes statiques et propriétés statiques.

Note:
À partir de PHP 8.1.0, appeler une méthode statique ou accéder à une propriété statique directement sur un trait est obsolète. Les méthodes et propriétés statiques devraient seulement être accédé sur une classe utilisant le trait.

Exemple #9 Variables statiques

<?php
trait Counter {
    public function inc() {
        static $c = 0;
        $c = $c + 1;
        echo "$c\n";
    }
}

class C1 {
    use Counter;
}

class C2 {
    use Counter;
}

$o = new C1(); $o->inc(); // echo 1
$p = new C2(); $p->inc(); // echo 1
?>

Exemple #10 Méthodes statiques

<?php
trait StaticExample {
    public static function doSomething() {
        return 'Doing something';
    }
}

class Example {
    use StaticExample;
}

Example::doSomething();
?>

Exemple #11 Propriétés statiques

<?php
trait StaticExample {
    public static $static = 'foo';
}

class Example {
    use StaticExample;
}

echo Example::$static;
?>

Propriétés

Les traits peuvent aussi définir des propriétés.

Exemple #12 Définir des propriétés

<?php
trait PropertiesTrait {
    public $x = 1;
}

class PropertiesExample {
    use PropertiesTrait;
}

$example = new PropertiesExample;
$example->x;
?>

Si un trait définit une propriété, alors la classe ne peut pas définir une propriété de même nom sauf si elle est compatible (même visibilité, type, modificateur readonly, valeur initiale), sinon une erreur fatale est émise.

Exemple #13 Résolution des conflits

<?php
trait PropertiesTrait {
    public $same = true;
    public $different1 = false;
    public bool $different2;
    public bool $different3;
}

class PropertiesExample {
    use PropertiesTrait;
    public $same = true;
    public $different1 = true; // Fatal error
    public string $different2; // Fatal error
    readonly protected bool $different3; // Fatal error
}
?>

Constantes

Les traits peuvent, à partir de PHP 8.2.0, aussi définir des constantes.

Exemple #14 Trait définissant une constante

<?php
trait ConstantsTrait {
    public const FLAG_MUTABLE = 1;
    final public const FLAG_IMMUTABLE = 5;
}

class ConstantsExample {
    use ConstantsTrait;
}

$example = new ConstantsExample;
echo $example::FLAG_MUTABLE; // 1
?>

Si un trait définit une constante, alors une classe ne peut pas définir une constante avec le même nom, à moins qu'elle ne soit compatible (même visibilité, même valeur, etc.), sinon une erreur fatale est émise.

Exemple #15 Résolution de conflit

<?php
trait ConstantsTrait {
    public const FLAG_MUTABLE = 1;
    final public const FLAG_IMMUTABLE = 5;
}

class ConstantsExample {
    use ConstantsTrait;
    public const FLAG_IMMUTABLE = 5; // Fatal error
}
?>

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User Contributed Notes 25 notes

down

656

Safak Ozpinar / safakozpinar at gmail ¶

12 years ago

Unlike inheritance; if a trait has static properties, each class using that trait has independent instances of those properties.

Example using parent class:
<?php
class TestClass {
    public static $_bar;
}
class Foo1 extends TestClass { }
class Foo2 extends TestClass { }
Foo1::$_bar = 'Hello';
Foo2::$_bar = 'World';
echo Foo1::$_bar . ' ' . Foo2::$_bar; // Prints: World World
?>

Example using trait:
<?php
trait TestTrait {
    public static $_bar;
}
class Foo1 {
    use TestTrait;
}
class Foo2 {
    use TestTrait;
}
Foo1::$_bar = 'Hello';
Foo2::$_bar = 'World';
echo Foo1::$_bar . ' ' . Foo2::$_bar; // Prints: Hello World
?>

down

454

greywire at gmail dot com ¶

12 years ago

The best way to understand what traits are and how to use them is to look at them for what they essentially are:  language assisted copy and paste.

If you can copy and paste the code from one class to another (and we've all done this, even though we try not to because its code duplication) then you have a candidate for a trait.

down

248

Stefan W ¶

11 years ago

Note that the "use" operator for traits (inside a class) and the "use" operator for namespaces (outside the class) resolve names differently. "use" for namespaces always sees its arguments as absolute (starting at the global namespace):

<?php
namespace Foo\Bar;
use Foo\Test;  // means \Foo\Test - the initial \ is optional
?>

On the other hand, "use" for traits respects the current namespace:

<?php
namespace Foo\Bar;
class SomeClass {
    use Foo\Test;   // means \Foo\Bar\Foo\Test
}
?>

Together with "use" for closures, there are now three different "use" operators. They all mean different things and behave differently.

down

JustAddingSomeAdditionalUseCase ¶

1 year ago

I have not seen this specific use case:

"Wanting to preserve action of parent class method, the trait one calling ::parent & also the child class mehod action".

// Child class.
use SuperTrait {
  initialize as initializeOr;
}
public function initialize(array &$element) {
  ...
  $this->initializeOr($element);
}
// Trait.
public function initialize(array &$element) {
  ...
  parent::initialize($element);
}
// Parent class.
public function initialize(array &$element) {
  ...
}

down

105

t8 at AT pobox dot com ¶

12 years ago

Another difference with traits vs inheritance is that methods defined in traits can access methods and properties of the class they're used in, including private ones.

For example:
<?php
trait MyTrait
{
  protected function accessVar()
  {
    return $this->var;
  }

}

class TraitUser
{
  use MyTrait;

  private $var = 'var';

  public function getVar()
  {
    return $this->accessVar();
  }
}

$t = new TraitUser();
echo $t->getVar(); // -> 'var'                                                                                                                                                                                                                          

?>

down

chris dot rutledge at gmail dot com ¶

12 years ago

It may be worth noting here that the magic constant __CLASS__ becomes even more magical - __CLASS__ will return the name of the class in which the trait is being used.

for example

<?php
trait sayWhere {
    public function whereAmI() {
        echo __CLASS__;
    }
}

class Hello {
    use sayWHere;
}

class World {
    use sayWHere;
}

$a = new Hello;
$a->whereAmI(); //Hello

$b = new World;
$b->whereAmI(); //World
?>

The magic constant __TRAIT__ will giev you the name of the trait

down

qeremy (!) gmail ¶

9 years ago

Keep in mind; "final" keyword is useless in traits when directly using them, unlike extending classes / abstract classes.

<?php
trait Foo {
    final public function hello($s) { print "$s, hello!"; }
}
class Bar {
    use Foo;
    // Overwrite, no error
    final public function hello($s) { print "hello, $s!"; }
}

abstract class Foo {
    final public function hello($s) { print "$s, hello!"; }
}
class Bar extends Foo {
    // Fatal error: Cannot override final method Foo::hello() in ..
    final public function hello($s) { print "hello, $s!"; }
}
?>

But this way will finalize trait methods as expected;

<?php
trait FooTrait {
    final public function hello($s) { print "$s, hello!"; }
}
abstract class Foo {
    use FooTrait;
}
class Bar extends Foo {
    // Fatal error: Cannot override final method Foo::hello() in ..
    final public function hello($s) { print "hello, $s!"; }
}
?>

down

yeu_ym at yahoo dot com ¶

5 years ago

Here is an example how to work with visiblity and conflicts.

<?php

trait A
{
    private function smallTalk()
    {
        echo 'a';
    }

    private function bigTalk()
    {
        echo 'A';
    }
}

trait B
{
    private function smallTalk()
    {
        echo 'b';
    }

    private function bigTalk()
    {
        echo 'B';
    }
}

trait C
{
    public function smallTalk()
    {
        echo 'c';
    }

    public function bigTalk()
    {
        echo 'C';
    }
}

class Talker
{
    use A, B, C {
        //visibility for methods that will be involved in conflict resolution
        B::smallTalk as public;
        A::bigTalk as public;

        //conflict resolution
        B::smallTalk insteadof A, C;
        A::bigTalk insteadof B, C;

        //aliases with visibility change
        B::bigTalk as public Btalk;
        A::smallTalk as public asmalltalk;
        
        //aliases only, methods already defined as public
        C::bigTalk as Ctalk;
        C::smallTalk as cmallstalk;
    }

}

(new Talker)->bigTalk();//A
(new Talker)->Btalk();//B
(new Talker)->Ctalk();//C

(new Talker)->asmalltalk();//a
(new Talker)->smallTalk();//b
(new Talker)->cmallstalk();//c

down

canufrank ¶

8 years ago

A number of the notes make incorrect assertions about trait behaviour because they do not extend the class.

So, while "Unlike inheritance; if a trait has static properties, each class using that trait has independent instances of those properties.

Example using parent class:
<?php
class TestClass {
    public static $_bar;
}
class Foo1 extends TestClass { }
class Foo2 extends TestClass { }
Foo1::$_bar = 'Hello';
Foo2::$_bar = 'World';
echo Foo1::$_bar . ' ' . Foo2::$_bar; // Prints: World World
?>

Example using trait:
<?php
trait TestTrait {
    public static $_bar;
}
class Foo1 {
    use TestTrait;
}
class Foo2 {
    use TestTrait;
}
Foo1::$_bar = 'Hello';
Foo2::$_bar = 'World';
echo Foo1::$_bar . ' ' . Foo2::$_bar; // Prints: Hello World
?>"

shows a correct example, simply adding
<?php
require_once('above');
class Foo3 extends Foo2 {
}
Foo3::$_bar = 'news';
echo Foo1::$_bar . ' ' . Foo2::$_bar . ' ' . Foo3::$_bar; 

// Prints: Hello news news

I think the best conceptual model of an incorporated trait is an advanced insertion of text, or as someone put it "language assisted copy and paste." If Foo1 and Foo2 were defined with $_bar, you would not expect them to share the instance. Similarly, you would expect Foo3 to share with Foo2, and it does.

Viewing this way explains away a lot of  the 'quirks' that are observed above with final, or subsequently declared private vars,

down

rawsrc ¶

6 years ago

About the (Safak Ozpinar / safakozpinar at gmail)'s great note, you can still have the same behavior than inheritance using trait with this approach : 
<?php

trait TestTrait {
    public static $_bar;
}

class FooBar {
    use TestTrait;
}

class Foo1 extends FooBar {

}
class Foo2 extends FooBar {

}
Foo1::$_bar = 'Hello';
Foo2::$_bar = 'World';
echo Foo1::$_bar . ' ' . Foo2::$_bar; // Prints: World World

down

balbuf ¶

8 years ago

(It's already been said, but for the sake of searching on the word "relative"...)

The "use" keyword to import a trait into a class will resolve relative to the current namespace and therefore should include a leading slash to represent a full path, whereas "use" at the namespace level is always absolute.

down

marko at newvibrations dot net ¶

8 years ago

As already noted, static properties and methods in trait could be accessed directly using trait. Since trait is language assisted c/p, you should be aware that static property from trait will be initialized to the value trait property had in the time of class declaration. 

Example:

<?php

trait Beer {
    protected static $type = 'Light';
    public static function printed(){
        echo static::$type.PHP_EOL;
    }
    public static function setType($type){
        static::$type = $type;
    }
}

class Ale {
    use Beer;
}

Beer::setType("Dark");

class Lager {
    use Beer;
}

Beer::setType("Amber");

header("Content-type: text/plain");

Beer::printed();  // Prints: Amber
Ale::printed();   // Prints: Light
Lager::printed(); // Prints: Dark

?>

down

qschuler at neosyne dot com ¶

10 years ago

Note that you can omit a method's inclusion by excluding it from one trait in favor of the other and doing the exact same thing in the reverse way.

<?php

trait A {
    public function sayHello()
    {
        echo 'Hello from A';
    }

    public function sayWorld()
    {
        echo 'World from A';
    }
}

trait B {
    public function sayHello()
    {
        echo 'Hello from B';
    }

    public function sayWorld()
    {
        echo 'World from B';
    }
}

class Talker {
    use A, B {
        A::sayHello insteadof B;
        A::sayWorld insteadof B;
        B::sayWorld insteadof A;
    }
}

$talker = new Talker();
$talker->sayHello();
$talker->sayWorld();

?>

The method sayHello is imported, but the method sayWorld is simply excluded.

down

Edward ¶

12 years ago

The difference between Traits and multiple inheritance is in the inheritance part.   A trait is not inherited from, but rather included or mixed-in, thus becoming part of "this class".   Traits also provide a more controlled means of resolving conflicts that inevitably arise when using multiple inheritance in the few languages that support them (C++).  Most modern languages are going the approach of a "traits" or "mixin" style system as opposed to multiple-inheritance, largely due to the ability to control ambiguities if a method is declared in multiple "mixed-in" classes.

Also, one can not "inherit" static member functions in multiple-inheritance.

down

ryan at derokorian dot com ¶

12 years ago

Simple singleton trait.

<?php

trait singleton {    
    /**
     * private construct, generally defined by using class
     */
    //private function __construct() {}
    
    public static function getInstance() {
        static $_instance = NULL;
        $class = __CLASS__;
        return $_instance ?: $_instance = new $class;
    }
    
    public function __clone() {
        trigger_error('Cloning '.__CLASS__.' is not allowed.',E_USER_ERROR);
    }
    
    public function __wakeup() {
        trigger_error('Unserializing '.__CLASS__.' is not allowed.',E_USER_ERROR);
    }
}

/**
 * Example Usage
 */

class foo {
    use singleton;
    
    private function __construct() {
        $this->name = 'foo';
    }
}

class bar {
    use singleton;
    
    private function __construct() {
        $this->name = 'bar';
    }
}

$foo = foo::getInstance();
echo $foo->name;

$bar = bar::getInstance();
echo $bar->name;

down

katrinaelaine6 at gmail dot com ¶

7 years ago

Adding to "atorich at gmail dot com":

The behavior of the magic constant __CLASS__ when used in traits is as expected if you understand traits and late static binding (http://php.net/manual/en/language.oop5.late-static-bindings.php).

<?php

$format = 'Class: %-13s | get_class(): %-13s | get_called_class(): %-13s%s';

trait TestTrait {
    public function testMethod() {
        global $format;
        printf($format, __CLASS__, get_class(), get_called_class(), PHP_EOL);
    }
    
    public static function testStatic() {
        global $format;
        printf($format, __CLASS__, get_class(), get_called_class(), PHP_EOL);
    }
}

trait DuplicateTrait {
    public function duplMethod() {
        global $format;
        printf($format, __CLASS__, get_class(), get_called_class(), PHP_EOL);
    }
    
    public static function duplStatic() {
        global $format;
        printf($format, __CLASS__, get_class(), get_called_class(), PHP_EOL);
    }
}

abstract class AbstractClass {
    
    use DuplicateTrait;
    
    public function absMethod() {
        global $format;
        printf($format, __CLASS__, get_class(), get_called_class(), PHP_EOL);
    }
    
    public static function absStatic() {
        global $format;
        printf($format, __CLASS__, get_class(), get_called_class(), PHP_EOL);
    }
}

class BaseClass extends AbstractClass {
    use TestTrait;
}

class TestClass extends BaseClass { }

$t = new TestClass();

$t->testMethod();
TestClass::testStatic();

$t->absMethod();
TestClass::absStatic();

$t->duplMethod();
TestClass::duplStatic();

?>

Will output:

Class: BaseClass     | get_class(): BaseClass     | get_called_class(): TestClass    
Class: BaseClass     | get_class(): BaseClass     | get_called_class(): TestClass    
Class: AbstractClass | get_class(): AbstractClass | get_called_class(): TestClass    
Class: AbstractClass | get_class(): AbstractClass | get_called_class(): TestClass    
Class: AbstractClass | get_class(): AbstractClass | get_called_class(): TestClass    
Class: AbstractClass | get_class(): AbstractClass | get_called_class(): TestClass

Since Traits are considered literal "copying/pasting" of code, it's clear how the methods defined in DuplicateTrait give the same results as the methods defined in AbstractClass.

down

D. Marti ¶

12 years ago

Traits are useful for strategies, when you want the same data to be handled (filtered, sorted, etc) differently.

For example, you have a list of products that you want to filter out based on some criteria (brands, specs, whatever), or sorted by different means (price, label, whatever). You can create a sorting trait that contains different functions for different sorting types (numeric, string, date, etc). You can then use this trait not only in your product class (as given in the example), but also in other classes that need similar strategies (to apply a numeric sort to some data, etc).

<?php
trait SortStrategy {
    private $sort_field = null;
    private function string_asc($item1, $item2) {
        return strnatcmp($item1[$this->sort_field], $item2[$this->sort_field]);
    }
    private function string_desc($item1, $item2) {
        return strnatcmp($item2[$this->sort_field], $item1[$this->sort_field]);
    }
    private function num_asc($item1, $item2) {
        if ($item1[$this->sort_field] == $item2[$this->sort_field]) return 0;
        return ($item1[$this->sort_field] < $item2[$this->sort_field] ? -1 : 1 );
    }
    private function num_desc($item1, $item2) {
        if ($item1[$this->sort_field] == $item2[$this->sort_field]) return 0;
        return ($item1[$this->sort_field] > $item2[$this->sort_field] ? -1 : 1 );
    }
    private function date_asc($item1, $item2) {
        $date1 = intval(str_replace('-', '', $item1[$this->sort_field]));
        $date2 = intval(str_replace('-', '', $item2[$this->sort_field]));
        if ($date1 == $date2) return 0;
        return ($date1 < $date2 ? -1 : 1 );
    }
    private function date_desc($item1, $item2) {
        $date1 = intval(str_replace('-', '', $item1[$this->sort_field]));
        $date2 = intval(str_replace('-', '', $item2[$this->sort_field]));
        if ($date1 == $date2) return 0;
        return ($date1 > $date2 ? -1 : 1 );
    }
}

class Product {
    public $data = array();
    
    use SortStrategy;
    
    public function get() {
        // do something to get the data, for this ex. I just included an array
        $this->data = array(
            101222 => array('label' => 'Awesome product', 'price' => 10.50, 'date_added' => '2012-02-01'),
            101232 => array('label' => 'Not so awesome product', 'price' => 5.20, 'date_added' => '2012-03-20'),
            101241 => array('label' => 'Pretty neat product', 'price' => 9.65, 'date_added' => '2012-04-15'),
            101256 => array('label' => 'Freakishly cool product', 'price' => 12.55, 'date_added' => '2012-01-11'),
            101219 => array('label' => 'Meh product', 'price' => 3.69, 'date_added' => '2012-06-11'),
        );
    }
    
    public function sort_by($by = 'price', $type = 'asc') {
        if (!preg_match('/^(asc|desc)$/', $type)) $type = 'asc';
        switch ($by) {
            case 'name':
                $this->sort_field = 'label';
                uasort($this->data, array('Product', 'string_'.$type));
            break;
            case 'date':
                $this->sort_field = 'date_added';
                uasort($this->data, array('Product', 'date_'.$type));
            break;
            default:
                $this->sort_field = 'price';
                uasort($this->data, array('Product', 'num_'.$type));
        }
    }
}

$product = new Product();
$product->get();
$product->sort_by('name');
echo '<pre>'.print_r($product->data, true).'</pre>';
?>

down

bscheshirwork at gmail dot com ¶

7 years ago

https://3v4l.org/mFuQE

1. no deprecate if same-class-named method get from trait
2. replace same-named method ba to aa in C

trait ATrait {
    public function a(){
        return 'Aa';
    }
}

trait BTrait {
    public function a(){
        return 'Ba';
    }
}

class C {
    use ATrait{
        a as aa;
    }
    use BTrait{
        a as ba;
    }
    
    public function a() {
        return static::aa() . static::ba();
    }
}

$o = new C;
echo $o->a(), "\n";

class D {
    use ATrait{
        ATrait::a as aa;
    }
    use BTrait{
        BTrait::a as ba;
    }
    
    public function a() {
        return static::aa() . static::ba();
    }
}

$o = new D;
echo $o->a(), "\n";

class E {
    use ATrait{
        ATrait::a as aa;
        ATrait::a insteadof BTrait;
    }
    use BTrait{
        BTrait::a as ba;
    }
    
    public function e() {
        return static::aa() . static::ba();
    }
}

$o = new E;
echo $o->e(), "\n";

class F {
    use ATrait{
        a as aa;
    }
    use BTrait{
        a as ba;
    }
    
    public function f() {
        return static::aa() . static::ba();
    }
}

$o = new F;
echo $o->f(), "\n";

AaAa 
AaBa 

Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; E has a deprecated constructor in /in/mFuQE on line 48 
AaBa 

Fatal error: Trait method a has not been applied, because there are collisions with other trait methods on F in /in/mFuQE on line 65

down

Kristof ¶

10 years ago

don't forget you can create complex (embedded) traits as well

<?php
trait Name {
  // ...
}
trait Address {
  // ...
}
trait Telephone {
  // ...
}
trait Contact {
  use Name, Address, Telephone;
}
class Customer {
  use Contact;
}
class Invoce {
  use Contact;
}
?>

down

Carlos Alberto Bertholdo Carucce ¶

8 years ago

If you want to resolve name conflicts and also change the visibility of a trait method, you'll need to declare both in the same line:

trait testTrait{
    
    public function test(){
        echo 'trait test';
    }
    
}

class myClass{
    
    use testTrait {
        testTrait::test as private testTraitF;
    }
    
    public function test(){
        echo 'class test';
        echo '<br/>';
        $this->testTraitF();
    }
    
}

$obj = new myClass(); 
$obj->test(); //prints both 'trait test' and 'class test'
$obj->testTraitF(); //The method is not accessible (Fatal error: Call to private method myClass::testTraitF() )

down

Oddant ¶

11 years ago

I think it's obvious to notice that using 'use' followed by the traits name must be seen as just copying/pasting lines of code into the place where they are used.

down

guidobelluomo at gmail dot com ¶

4 years ago

If you override a method which was defined by a trait, calling the parent method will also call the trait's override. Therefore if you need to derive from a class which has a trait, you can extend the class without losing the trait's functionality:

<?php

trait ExampleTrait
{
    public function output()
    {
        parent::output();
        echo "bar<br>";
    }
}

class Foo
{
    public function output()
    {
        echo "foo<br>";
    }
}

class FooBar extends Foo
{
    use ExampleTrait;
}

class FooBarBaz extends FooBar
{
    use ExampleTrait;
    public function output()
    {
        parent::output();
        echo "baz";
    }
}

(new FooBarBaz())->output();
?>

Output:
foo
bar
baz

down

84td84 at gmail dot com ¶

9 years ago

A note to 'Beispiel #9 Statische Variablen'. A trait can also have a static property:

trait Counter {
    static $trvar=1;

    public static function stfunc() {
        echo "Hello world!"
    }
}

class C1 {
    use Counter;
}

print "\nTRVAR: " . C1::$trvar . "\n";   //prints 1

$obj = new C1();
C1::stfunc();   //prints  Hello world!
$obj->stfunc();   //prints Hello world!

A static property (trvar) can only be accessed using the classname (C1).
But a static function (stfunc) can be accessed using the classname or the instance ($obj).

down

cody at codysnider dot com ¶

7 years ago

/*
DocBlocks pertaining to the class or trait will NOT be carried over when applying the trait.

Results trying a couple variations on classes with and without DocBlocks that use a trait with a DocBlock
*/

<?php

/**
 * @Entity
 */
trait Foo
{
    protected $foo;
}

/**
 * @HasLifecycleCallbacks
 */
class Bar
{
    use \Foo;
    
    protected $bar;
}

class MoreBar
{
    use \Foo;
    
    protected $moreBar;
}

$w = new \ReflectionClass('\Bar');
echo $w->getName() . ":\r\n";
echo $w->getDocComment() . "\r\n\r\n";

$x = new \ReflectionClass('\MoreBar');
echo $x->getName() . ":\r\n";
echo $x->getDocComment() . "\r\n\r\n";

$barObj = new \Bar();
$y = new \ReflectionClass($barObj);
echo $y->getName() . ":\r\n";
echo $y->getDocComment() . "\r\n\r\n";

foreach($y->getTraits() as $traitObj) {
    echo $y->getName() . " ";
    echo $traitObj->getName() . ":\r\n";
    echo $traitObj->getDocComment() . "\r\n";
}

$moreBarObj = new \MoreBar();
$z = new \ReflectionClass($moreBarObj);
echo $z->getName() . " ";
echo $z->getDocComment() . "\r\n\r\n";

foreach($z->getTraits() as $traitObj) {
    echo $z->getName() . " ";
    echo $traitObj->getName() . ":\r\n";
    echo $traitObj->getDocComment() . "\r\n";
}

down

artur at webprojektant dot pl ¶

12 years ago

Trait can not have the same name as class because it will show: Fatal error: Cannot redeclare class

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