PHP 5.5.16 is released

Traits

自 PHP 5.4.0 起,PHP 实现了代码复用的一个方法,称为 traits。

Traits 是一种为类似 PHP 的单继承语言而准备的代码复用机制。Trait 为了减少单继承语言的限制,使开发人员能够自由地在不同层次结构内独立的类中复用方法集。Traits 和类组合的语义是定义了一种方式来减少复杂性,避免传统多继承和混入类(Mixin)相关的典型问题。

Trait 和一个类相似,但仅仅旨在用细粒度和一致的方式来组合功能。Trait 不能通过它自身来实例化。它为传统继承增加了水平特性的组合;也就是说,应用类的成员不需要继承。

Example #1 Trait 示例

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

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

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

优先级

从基类继承的成员被 trait 插入的成员所覆盖。优先顺序是来自当前类的成员覆盖了 trait 的方法,而 trait 则覆盖了被继承的方法。

Example #2 优先顺序示例

从基类继承的成员被插入的 SayWorld Trait 中的 MyHelloWorld 方法所覆盖。其行为 MyHelloWorld 类中定义的方法一致。优先顺序是当前类中的方法会覆盖 trait 方法,而 trait 方法又覆盖了基类中的方法。

<?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();
?>

以上例程会输出:

Hello World!

Example #3 另一个优先级顺序的例子

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

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

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

以上例程会输出:

Hello Universe!

多个 trait

通过逗号分隔,在 use 声明列出多个 trait,可以都插入到一个类中。

Example #4 多个 trait 的用法

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

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

class 
MyHelloWorld {
    use 
HelloWorld;
    public function 
sayExclamationMark() {
        echo 
'!';
    }
}

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

以上例程会输出:

Hello World!

冲突的解决

如果两个 trait 都插入了一个同名的方法,如果没有明确解决冲突将会产生一个致命错误。

为了解决多个 trait 在同一个类中的命名冲突,需要使用 insteadof 操作符来明确指定使用冲突方法中的哪一个。

以上方式仅允许排除掉其它方法,as 操作符可以将其中一个冲突的方法以另一个名称来引入。

Example #5 冲突的解决

在本例中 Talker 使用了 trait A 和 B。由于 A 和 B 有冲突的方法,其定义了使用 trait B 中的 smallTalk 以及 trait A 中的 bigTalk。

Aliased_Talker 使用了 as 操作符来定义了 talk 来作为 B 的 bigTalk 的别名。

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

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

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

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

修改方法的访问控制

使用 as 语法还可以用来调整方法的访问控制。

Example #6 修改方法的访问控制

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

// 修改 sayHello 的访问控制
class MyClass1 {
    use 
HelloWorld sayHello as protected; }
}

// 给方法一个改变了访问控制的别名
// 原版 sayHello 的访问控制则没有发生变化
class MyClass2 {
    use 
HelloWorld sayHello as private myPrivateHello; }
}
?>

从 trait 来组成 trait

正如类能够使用 trait 一样,其它 trait 也能够使用 trait。在 trait 定义时通过使用一个或多个 trait,它能够组合其它 trait 中的部分或全部成员。

Example #7 从 trait 来组成 trait

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

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

trait 
HelloWorld {
    use 
HelloWorld;
}

class 
MyHelloWorld {
    use 
HelloWorld;
}

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

以上例程会输出:

Hello World!

Trait 的抽象成员

为了对使用的类施加强制要求,trait 支持抽象方法的使用。

Example #8 表示通过抽象方法来进行强制要求

<?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;
    }
}
?>

Trait 的静态成员

Traits 可以被静态成员静态方法定义。

Example #9 静态变量

<?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
?>

Example #10 静态方法

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

class 
Example {
    use 
StaticExample;
}

Example::doSomething();
?>

属性

Trait 同样可以定义属性。

Example #11 定义属性

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

class 
PropertiesExample {
    use 
PropertiesTrait;
}

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

如果 trait 定义了一个属性,那类将不能定义同样名称的属性,否则会产生一个错误。如果该属性在类中的定义与在 trait 中的定义兼容(同样的可见性和初始值)则错误的级别是 E_STRICT,否则是一个致命错误。

Example #12 解决冲突

<?php
trait PropertiesTrait {
    public 
$same true;
    public 
$different false;
}

class 
PropertiesExample {
    use 
PropertiesTrait;
    public 
$same true// Strict Standards
    
public $different true// 致命错误
}
?>
add a note add a note

User Contributed Notes 26 notes

up
86
Safak Ozpinar / safakozpinar at gmail
2 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
33
Stefan W
1 year 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
32
chris dot rutledge at gmail dot com
2 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
7
atorich at gmail dot com
9 months 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
5
Kristof
2 months 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;
}
?>
up
34
greywire at gmail dot com
2 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
34
ryan at derokorian dot com
2 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
19
t8 at AT pobox dot com
2 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
8
anthony bishopric
2 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
8
Edward
2 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.
up
12
karolis at iwsolutions dot ie
2 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
13
Anonymous
2 years ago
Traits can not implement interfaces.
(should be obvious, but tested is tested)
up
9
Jason dot Hofer dot deletify dot this dot part at gmail dot com
2 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. */
}

?>
up
8
D. Marti
1 year 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>';
?>
up
1
contato at williamsantana dot com dot br
1 year ago
Please note that a trait cannot extend a class. Traits can only contain another traits by using 'use' keyword. Things like

<?php
   
trait DetailedException extends Exception {}
?>

will not work. Be careful.

Cheers.
up
1
ryanhanekamp at yahoo dot com
2 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
0
qschuler at neosyne dot com
6 months 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
0
majoro chitetskoy at gmail dot com
8 months ago
Some extreme Trait testing, which anyone can find useful. This involves what can be called as "Trait Inheritance" though I doubt if that is a proper word. This shows how to have some sort of inheritance in Traits.

Snippet from one complex Tristan Engine code.

<?php
/**
* Trait and Helper Backbone class
*/
trait Foo_HlpBbT {
      function 
mnInfo_gst($x=null, $c=false){
        echo
"Foo_HlpBbT has been called\n";
      }
}

/**
* Base Archvie
*/
class Foo_BaseArchive {
    use
Foo_HlpBbT;
   
   
// accessor properties
   
public    $_mnInfo;
}

/**
* Testing Archive
*/
class Foo_ItemArchvie extends
   
Foo_BaseArchive
{
}

/**
* Testing Archive 2
*/
/**
* The base handler for sub base handler
*/
trait Foo_Item_HlpBbT {
    use
Foo_HlpBbT;

    function
mnInfo_gst($x=null, $c=false){
       
parent::mnInfo_gst($x,$c);
        echo
"Foo_Item_HlpBbT is called.\n";
    }
}

/**
* The base handler for sub base handler
*/
trait Foo_Item_HlpBbT2 {
    use
Foo_Item_HlpBbT {
       
Foo_Item_HlpBbT::mnInfo_gst as _e1_mnInfo_gst;
    }

   
// We need that the Foo_HlpBbT::mnInfo_gst, Foo_Item_HlpBbT::mnInfo_gst and this mnInfo_gst is called.
    // Troubles here, only the Foo_HlpBbT and this is called, the Foo_Item_HlpBbT is skipped.
    // So it's important that if necessary, the function that is intended to be "overriden" from
    // the trait inheritances be aliased like what we did to mnInfo_gst.
   
function mnInfo_gst($x=null, $c=false){
       
$this->_e1_mnInfo_gst($x,$c);
        echo
"Foo_Item_HlpBbT2 is called.\n";
    }
}

/**
* The base handler for sub base handler
*/
trait Foo_Item_HlpBbT3 {
    use
Foo_Item_HlpBbT2 {
       
Foo_Item_HlpBbT2::mnInfo_gst as _e2_mnInfo_gst;
    }

   
// Another deeper Trait declaration
   
function mnInfo_gst($x=null, $c=false){
       
$this->_e2_mnInfo_gst($x,$c);
        echo
"Foo_Item_HlpBbT3 is called.\n";
    }
}

/**
* Item Archive
*/
class Foo_Item_ItemArchive extends
   
Foo_BaseArchive
{
    use
Foo_Item_HlpBbT3;
}

// Testing na
$tang = new Foo_Item_ItemArchive();
$tang->mnInfo_gst();
?>
outputs:

Foo_HlpBbT has been called
Foo_Item_HlpBbT is called.
Foo_Item_HlpBbT2 is called.
Foo_Item_HlpBbT3 is called.
up
-1
tomasz at marcinkowski dot pl
6 months ago
Unlike the __CLASS__ constant, which returns name of a class implementing a trait, the __METHOD__ constant returns the trait method name. You might find it useful.

Example:

<?php

namespace XXX;

trait
Ta {
  public function
test1() {
    return
sprintf('class: %s, method: %s, trait: %s', __CLASS__, __METHOD__, __TRAIT__);
  }
}

class
A {
  use
Ta;
}

$a = new A();
var_dump($a->test1()); // class: XXX\A, method: XXX\Ta::test1, trait: XXX\Ta

?>
up
0
Oddant
1 year 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
0
Serafim
1 year ago
Another useful property of traits:
<?php
namespace Traits;
trait
Properties{
    public function
__get($var){
       
$var = '_' . $var;
       
$getter = '_get' . $var;
       
        if(
method_exists($this, $getter)){
            try{
               
$val = $this->$getter();
            }catch(\
Exception $e){
                throw new \
Exception($e);
            }
            return
$val;
        }
        throw new \
Exception('Can not get property: ' . $var . ', method ' . $getter . ' not exists');
    }
   
    public function
__set($var, $val){
       
$var = '_' . $var;
       
$setter = '_set' . $var;
       
        if(
method_exists($this->$setter) && isset($this->$var)){
            try{
               
$setval = $this->$setter($val);
            }catch(\
Exception $e){
                throw new \
Exception($e);
            }
           
$this->$var = ($setval === NULL) ? $this->$var : $setval;
        }else{
            throw new \
Exception('Can not set property: ' . $var . ', method ' . $setter . ' not exists');
        }
    }
}

class
Some{
  use \
Chidori\Traits\Properties;
 
 
// Magic begin
 
protected $_var = 42;
  protected function
_get_var(){ return $this->_var; }
  protected function
_set_var($val){ return NULL; }
}

$s = new Some();
$s->var = 23; \\ set value
echo $s->var; \\ return 42? where is my 23? =)
?>
up
0
artur at webprojektant dot pl
1 year ago
Trait can not have the same name as class because it will  show: Fatal error: Cannot redeclare class
up
-2
dario dot masamune at gmail dot com
2 years ago
Just in case someone was wondering, traits can be inside namespaces too! Cool!!
up
-1
atorich at gmail dot com
9 months 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
-2
peter at icb dot at
8 months ago
You cannot use a trait whos name is in a variable like:
<?php
trait mytrait { public $x; }

$tr = 'mytrait';
class
myclass
{
  use
$tr;
  ...
}
?>

If you really need that, you have to use eval:
<?php
eval("
class my_tmp_class { use
$tr; }
"
);

class
myclass extends my_tmp_class { ... }
?>
up
-5
syzer3 at gmail dot com
1 year ago
Traits can be useful to create Fluent API
ex:
trait StaticMake
{
    public static function make()
    {
        return new static();
    }
}
class HelloWorld
{
use StaticMake;

   public function getHello()
   {
      return "Hello World";
   }
}
//now instead:
$theHello = new HelloWorld;
echo $theHello -> getHello();

//one may just use
echo HelloWorld:make() -> getHello();
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