Traits

In PHP gibt es eine Methode der Wiederverwendung von Code, die Traits genannt wird.

Traits sind ein Mechanismus zur Wiederverwendung von Code, der in Programmiersprachen mit einfacher Vererbung wie PHP verwendet wird. Ein Trait kann verwendet werden, um den Beschränkungen der einfachen Vererbung auszuweichen, indem er erlaubt, dass Mengen von Methoden frei in mehreren unabhängigen Klassen, die in verschiedenen Klassenhierarchien stecken, wiederzuverwenden. Die Semantik der Kombination von Traits und Klassen ist so definiert, dass die Komplexität reduziert wird und die üblichen Probleme vermeidet, die mit Mehrfachvererbung und Mixins in Verbindung gebracht werden.

Ein Trait hat Ähnlichkeit mit einer Klasse, ist aber nur dafür vorgesehen, Funktionalität in einer feingranularen und konsistenten Art und Weise zu bündeln. Es ist nicht möglich einen Trait alleinstehend zu instantiieren. Es handelt sich um einen Zusatz zur traditionellen Vererbung und erlaubt horizontale Komposition von Verhaltensweisen, d. h. die Verwendung von Klassenmethoden ohne Vererbung vorauszusetzen.

Beispiel #1 Trait-Beispiel

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

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

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

Rangfolge

Methoden der aktuellen Klasse überschreiben Methoden, welche von Traits definiert wurden. Jene wiederum überschreiben von Elternklassen geerbte Methoden.

Beispiel #2 Rangfolge-Beispiel

Die Methode sayHello der Basisklasse wird durch die gleichnamige Methode aus dem Trait überschrieben.

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

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

class
MyHelloWorld extends Base {
use
SayWorld;
}

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

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

Hallo Welt!

Beispiel #3 Weiteres Beispiel für Rangfolge

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

class
TheWorldIsNotEnough {
use
HelloWorld;
public function
sayHello() {
echo
'Hallo Universum!';
}
}

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

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

Hallo Universum!

Mehrere Traits

Mehrere Traits können durch eine kommaseparierte Auflistung im use-Statement zu einer Klasse hinzugefügt werden.

Beispiel #4 Verwendung mehrerer Traits

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

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

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

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

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

Hallo Welt!

Konfliktauflösung

Falls zwei Traits eine Methode mit gleichem Namen einfügen, so wird ein Fatal Error erzeugt, wenn der Konflikt nicht explizit aufgelöst wird.

Um einen Namenskonflikt zwischen Traits in der gleichen Klasse aufzulösen muss der insteadof-Operator verwendet werden, um genau eine der Methoden des Konflikts auszuwählen.

Da dies es nur erlaubt Methoden auszuschließen kann der as-Operator verwendet werden, um einen Alias zu einer der Methoden hinzuzufügen. Es ist zu beachten, dass der as Operator die Methode nicht umbenennt, und auch keine andere Methode beeinflusst.

Beispiel #5 Konfliktauflösung

In diesem Beispiel verwendet die Klasse Talker die Traits A und B. Nachdem A und B sich widersprechende Methoden besitzen definiert die Klasse, dass sie die Variante von smallTalk aus dem Trait B und die Variante von bigTalk des Traits A verwenden möchte.

Die Klasse Aliased_Talker verwendet den as-Operator, damit sie außerdem die Implementierung der bigTalk-Methode von B unter dem Alias talk verwenden kann.

<?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;
}
}
?>

Veränderung der Sichtbarkeit von Methoden

Mit der as-Syntax ist es ebenso möglich, die Sichtbarkeit einer Methode in der darstellenden Klasse zu verändern.

Beispiel #6 Veränderung der Sichtbarkeit von Methoden

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

// Ändern der Sichtbarkeit von sayHello
class MyClass1 {
use
HelloWorld { sayHello as protected; }
}

// Alias der Methode mit geänderter Sichtbarkeit
// Die Sichtbarkeit von sayHello bleibt unverändert
class MyClass2 {
use
HelloWorld { sayHello as private myPrivateHello; }
}
?>

Trait-Zusammensetzung aus Traits

Ebenso wie Klassen können auch Traits andere Traits verwenden. Indem man einen oder mehrere Traits in einer Traitdefinition verwendet kann man Traits entweder teilweise oder vollständig aus Methoden, welche in anderen Traits definiert sind, zusammensetzen.

Beispiel #7 Trait-Zusammensetzung aus Traits

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

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

trait
HelloWorld {
use
Hello, World;
}

class
MyHelloWorld {
use
HelloWorld;
}

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

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

Hallo Welt!

Abstrakte Traitmember

Traits unterstützen auch die Verwendung von abstrakten Methoden, um darstellenden Klassen Anforderungen vorzugeben. Es werden öffentliche, geschützte und private Methoden unterstützt. Vor PHP 8.0.0 wurden nur öffentliche und geschützte abstrakte Methoden unterstützt.

Achtung

Seit PHP 8.0.0 muss die Signatur einer konkreten Methode den Regeln zur Signaturkompatibilität entsprechen; zuvor durfte ihre Signatur davon abweichen.

Beispiel #8 Ausdrücken von Anforderungen durch abstrakte Methoden

<?php
trait Hello {
public function
sayHelloWorld() {
echo
'Hallo'.$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;
}
}
?>

Statische Traitmember

Traits unterstützen sowohl statische Variablen, statische Methoden und statische Eignschaften.

Hinweis:

Seit PHP 8.1.0 sind der Aufruf einer statischen Methode oder der Zugriff auf eine statische Eigenschaft direkt in einem Trait veraltet. Auf statische Methoden und Eigenschaften sollte nur in einer Klasse zugegriffen werden, die den Trait verwendet.

Beispiel #9 Statische Variablen

<?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
?>

Beispiel #10 Statische Methoden

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

class
Example {
use
StaticExample;
}

Example::doSomething();
?>

Beispiel #11 Statische Eigenschaften

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

class
Example {
use
StaticExample;
}

echo
Example::$static;
?>

Eigenschaften

Traits können ebenfalls Eigenschaften definieren.

Beispiel #12 Eigenschaften definieren

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

class
PropertiesExample {
use
PropertiesTrait;
}

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

Definiert ein Trait eine Eigenschaft, dann kann eine Klasse keine Eigenschaft mit dem selben Namen definieren, es sei denn, sie ist kompatibel (selbe Sichtbarkeit und Typ, readonly-Modifikator und Initialwert); andernfalls wird ein fataler Fehler auftreten.

Beispiel #13 Konfliktauflösung

<?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
}
?>

Konstanten

Seit PHP 8.2.0 können Traits auch Konstanten definieren.

Beispiel #14 Definieren von Konstanten

<?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
?>

Wenn ein Trait eine Konstante definiert, kann eine Klasse keine Konstante mit demselben Namen definieren, es sei denn, sie ist kompatibel (dieselbe Sichtbarkeit, derselbe Initialwert und dieselbe Finalität), andernfalls wird ein fataler Fehler ausgegeben.

Beispiel #15 Konfliktauflösung

<?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
}
?>
add a note add a note

User Contributed Notes 37 notes

up
582
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
?>
up
406
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.
up
217
Stefan W
10 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.
up
87
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
up
51
qeremy (!) gmail
8 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!"; }
}
?>
up
77
atorich at gmail dot com
10 years ago
add to "chris dot rutledge at gmail dot com":
__CLASS__ will return the name of the class in which the trait is being used (!) not the class in which trait method is being called:

<?php
trait TestTrait {
    public function
testMethod() {
        echo
"Class: " . __CLASS__ . PHP_EOL;
        echo
"Trait: " . __TRAIT__ . PHP_EOL;
    }
}

class
BaseClass {
    use
TestTrait;
}

class
TestClass extends BaseClass {

}

$t = new TestClass();
$t->testMethod();

//Class: BaseClass
//Trait: TestTrait
up
12
rawsrc
5 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
up
72
t8 at AT pobox dot com
11 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'                                                                                                                                                                                                                         

?>
up
24
canufrank
7 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,
up
17
marko at newvibrations dot net
7 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

?>
up
41
karolis at iwsolutions dot ie
11 years ago
Not very obvious but trait methods can be called as if they were defined as static methods in a regular class

<?php
trait Foo {
    function
bar() {
        return
'baz';
    }
}

echo
Foo::bar(),"\\n";
?>
up
45
Anonymous
11 years ago
Traits can not implement interfaces.
(should be obvious, but tested is tested)
up
2
guidobelluomo at gmail dot com
3 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
up
13
Vasyl Sovyak
8 years ago
<?php
trait A
{
    public function
bar()
    {
        echo
'A::bar';
    }
}

trait
B
{
    public function
bar()
    {
        echo
'B::bar';
    }
}

trait
C
{
    public function
bar()
    {
        echo
'C::bar';
    }
}

class
Foo
{
    use
A, B, C {
       
C::bar insteadof A, B;
    }
}

$foo = new Foo();
$foo->bar(); //C::bar
up
6
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.
up
21
anthony bishopric
12 years ago
The magic method __call works as expected using traits.

<?php
trait Call_Helper{
   
    public function
__call($name, $args){
        return
count($args);
    }
}

class
Foo{
    use
Call_Helper;
}

$foo = new Foo();
echo
$foo->go(1,2,3,4); // echoes 4
up
11
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.
up
5
cody at codysnider dot com
6 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";
}
up
43
ryan at derokorian dot com
11 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;
up
16
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.
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14
D. Marti
11 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>';
?>
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16
Jason dot Hofer dot deletify dot this dot part at gmail dot com
12 years ago
A (somewhat) practical example of trait usage.

Without traits:

<?php

class Controller {
 
/* Controller-specific methods defined here. */
}

class
AdminController extends Controller {
 
/* Controller-specific methods inherited from Controller. */
  /* Admin-specific methods defined here. */
}

class
CrudController extends Controller {
 
/* Controller-specific methods inherited from Controller. */
  /* CRUD-specific methods defined here. */
}

class
AdminCrudController extends CrudController {
 
/* Controller-specific methods inherited from Controller. */
  /* CRUD-specific methods inherited from CrudController. */
  /* (!!!) Admin-specific methods copied and pasted from AdminController. */
}

?>

With traits:

<?php

class Controller {
 
/* Controller-specific methods defined here. */
}

class
AdminController extends Controller {
 
/* Controller-specific methods inherited from Controller. */
  /* Admin-specific methods defined here. */
}

trait
CrudControllerTrait {
 
/* CRUD-specific methods defined here. */
}

class
AdminCrudController extends AdminController {
  use
CrudControllerTrait;
 
/* Controller-specific methods inherited from Controller. */
  /* Admin-specific methods inherited from AdminController. */
  /* CRUD-specific methods defined by CrudControllerTrait. */
}

?>
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12
Kristof
9 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;
}
?>
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8
ryanhanekamp at yahoo dot com
11 years ago
Using AS on a __construct method (and maybe other magic methods) is really, really bad. The problem is that is doesn't throw any errors, at least in 5.4.0. It just sporadically resets the connection. And when I say "sporadically," I mean that arbitrary changes in the preceding code can cause the browser connection to reset or not reset *consistently*, so that subsequent page refreshes will continue to hang, crash, or display perfectly in the same fashion as the first load of the page after a change in the preceding code, but the slightest change in the code can change this state. (I believe it is related to precise memory usage.)

I've spent a good part of the day chasing down this one, and weeping every time commenting or even moving a completely arbitrary section of code would cause the connection to reset. It was just by luck that I decided to comment the

"__construct as primitiveObjectConstruct"

line and then the crashes went away entirely.

My parent trait constructor was very simple, so my fix this time was to copy the functionality into the child __construct. I'm not sure how I'll approach a more complicated parent trait constructor.
up
2
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
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7
Anonymous
6 years ago
", но нельзя определить статические переменные в самом трейте." - зачем вводите людей в заблуждение?

Документация помечена как ооп5 (я не знаю с какой версии есть такая возможность, до сего дня верил вам и думал что нельзя), но учитывая что здесь и по более поздним версиям информация, то Вы как то пометьте что статические переменные могут быть в трейте не только в методах трейта, но и сами по себе свойствами трейта.
up
2
katrinaelaine6 at gmail dot com
6 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.
up
3
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).
up
1
bscheshirwork at gmail dot com
6 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
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2
tz at za-ek dot ru
6 years ago
I want to make flexible module that contains different functionality and I want to combine this but using the same methods:

<?php
class Brain {
    public function
ask($q) {
       
// Trate the question
       
return 'Some response';
    }
}

trait
BrainLogger {
    public function
ask($q) {
       
log('Received a question: ' . $q);
        return
parent::ask();
    }
}
trait
BrainMad {
    public function
ask($q) {
        if(
rand(0,1) == 1) {
               return
parent::ask($q);      
        } else {
               return
'I don\'t wanna talk with you.';
        }
    }
}
?>

In some part of my application I want to use different combinations of that functionality so if I want one brain instance:

<?php
$brain
= new Brain;
$brain->ask('what we gonna do tonight?');
?>

If I want log all received questions:

<?php
class NiceBrain extends Brain {
    use
BrainLog;
}
$brain = new Brain;
$brain->ask('what we gonna do tonight?'); // Will log
?>

If I want to extend more I need to make a cascade of classes:
<?php
class NiceBrain extends Brain {
    use
BrainLog;
}
class
CrazyBrain extends NiceBrain {
    use
BrainMad;
}
$brain = new CrazyBrain;
$brain->ask('What we gonna do tonight?');
// Will output  'I don't wanna talk with you.' or normal response
// but logging only in case BrainMad has a good mood
?>

Because using of multiple traits will call only one selected in section "use Trait;".
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3
Oddant
10 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.
up
1
Carlos Alberto Bertholdo Carucce
7 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() )
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2
artur at webprojektant dot pl
11 years ago
Trait can not have the same name as class because it will  show: Fatal error: Cannot redeclare class
up
1
Anonymous
3 years ago
Trait, utility, or inheritance?

You can view a trait as a collection of utility functions with access to $this, without first having to declare (or think about) which classes $this could belong to.

Anytime you want to carve out (a.k.a factor out, "cut & paste") a section of code that you want to use in other classes too, and you need $this, then you should put the code in a trait function.

Trait functions can also use $this to share data among each other.

If you don't need access to $this, you could carve out the code into a utility function or a separate utility class outside your original class. To share data among functions of a utility class you will have to pass around a utility object. Since a trait is more intimately tied in through $this, there is nothing you need to pass around.

Common functionality can also be factored out into a parent class. Such a parent class could sit in between a base class from a library and several child classes that you write. However, all your classes that use the common functionality must then inherit from the "in between" parent. This means they cannot be children from any other class. If the common functionality is general enough to be used with other base classes, you will end up having to duplicate ("copy & paste") the code into several "in between" classes. With a trait you won't have to, which in most cases makes it easier to update and improve the common functionality.
up
-1
aram dot petrosyan dot 88 at gmail dot com
9 years ago
It's possible to define abstract function in a trait as static and implement non-static version of the function , and it will works. Like this

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

class traitTest
{
    use B;

    public static function talk()
    {
        echo 111;
    }
}

Also, it's possible to define abstract non static , and implement static version.

Can't understand , is this a bug or it's a feature :)
up
-1
gulaschsuppe2 at gmail dot com
4 years ago
Like shown in other examples it is possible to define a constructors and destructors in traits:

<? php
    trait T {
        public $prop = null;

        public function __construct($prop) {
            echo "Constructor called\n";
            $this->prop = $prop;
        }

        public function __destruct() {
            echo "Destructor called\n";
        }
    }

    class A {
        use T;
    }

    $a = new A("Hello World\n"); // Constructor called
   
    echo $a->prop; // Hello World

    // Destructor called

?>

It is also possible to use trait methods as constructor/destructor using them with the alias '__construct'/'__destruct':

<?php
   
trait T {
        public
$prop = null;

        public function
constructor($prop) {
            echo
"Constructor called\n";
           
$this->prop = $prop;
        }

        public function
destructor() {
            echo
"Destructor called\n";
        }
    }

    class
A {
        use
T {
           
T::constructor as __construct;
           
T::destructor as __destruct;
        }
    }

   
$a = new A("Hello World\n"); // Constructor called
   
   
echo $a->prop; // Hello World

    // Destructor called   

?>
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-6
nobody
5 years ago
<?php
trait MyTrait {
    public function
sayHello() {
        echo
'Hello World! from MyTrait';
    }
}

class
MyClass1 {
    use
MyTrait;

    public function
sayHello() {
        echo
'Hello World from MyClasss!';
    }
}
$obj=new MyClass1();
$obj->sayHello(); //Hello World from MyClasss!⏎

?>
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