Interfaces de Objetos
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
?>
Traits
As of PHP 5.4.0, PHP implements a method of code reuse called Traits.
Traits are a mechanism for code reuse in single inheritance languages such as PHP. A Trait is intended to reduce some limitations of single inheritance by enabling a developer to reuse sets of methods freely in several independent classes living in different class hierarchies. The semantics of the combination of Traits and classes is defined in a way which reduces complexity, and avoids the typical problems associated with multiple inheritance and Mixins.
A Trait is similar to a class, but only intended to group functionality in a fine-grained and consistent way. It is not possible to instantiate a Trait on its own. It is an addition to traditional inheritance and enables horizontal composition of behavior; that is, the application of class members without requiring inheritance.
Exemplo #1 Trait example
<?php
trait ezcReflectionReturnInfo {
function getReturnType() { /*1*/ }
function getReturnDescription() { /*2*/ }
}
class ezcReflectionMethod extends ReflectionMethod {
use ezcReflectionReturnInfo;
/* ... */
}
class ezcReflectionFunction extends ReflectionFunction {
use ezcReflectionReturnInfo;
/* ... */
}
?>
Precedence
An inherited member from a base class is overridden by a member inserted by a Trait. The precedence order is that members from the current class override Trait methods, which in return override inherited methods.
Exemplo #2 Precedence Order Example
An inherited method from a base class is overridden by the method inserted into MyHelloWorld from the SayWorld Trait. The behavior is the same for methods defined in the MyHelloWorld class. The precedence order is that methods from the current class override Trait methods, which in turn override methods from the base class.
<?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();
?>
O exemplo acima irá imprimir:
Hello World!
Exemplo #3 Alternate Precedence Order Example
<?php
trait HelloWorld {
public function sayHello() {
echo 'Hello World!';
}
}
class TheWorldIsNotEnough {
use HelloWorld;
public function sayHello() {
echo 'Hello Universe!';
}
}
$o = new TheWorldIsNotEnough();
$o->sayHello();
?>
O exemplo acima irá imprimir:
Hello Universe!
Multiple Traits
Multiple Traits can be inserted into a class by listing them in the use statement, separated by commas.
Exemplo #4 Multiple Traits Usage
<?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();
?>
O exemplo acima irá imprimir:
Hello World!
Conflict Resolution
If two Traits insert a method with the same name, a fatal error is produced, if the conflict is not explicitly resolved.
To resolve naming conflicts between Traits used in the same class, the insteadof operator needs to be used to chose exactly one of the conflicting methods.
Since this only allows one to exclude methods, the as operator can be used to allow the inclusion of one of the conflicting methods under another name.
Exemplo #5 Conflict Resolution
In this example, Talker uses the traits A and B. Since A and B have conflicting methods, it defines to use the variant of smallTalk from trait B, and the variant of bigTalk from trait A.
The Aliased_Talker makes use of the as operator to be able to use B's bigTalk implementation under an additional alias 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;
}
}
?>
Changing Method Visibility
Using the as syntax, one can also adjust the visibility of the method in the exhibiting class.
Exemplo #6 Changing Method Visibility
<?php
trait HelloWorld {
public function sayHello() {
echo 'Hello World!';
}
}
// Change visibility of sayHello
class MyClass1 {
use HelloWorld { sayHello as protected; }
}
// Alias method with changed visibility
// sayHello visibility not changed
class MyClass2 {
use HelloWorld { sayHello as private myPrivateHello; }
}
?>
Traits Composed from Traits
Just as classes can make use of traits, so can other traits. By using one or more traits in a trait definition, it can be composed partially or entirely of the members defined in those other traits.
Exemplo #7 Traits Composed from 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();
$o->sayWorld();
?>
O exemplo acima irá imprimir:
Hello World!
Abstract Trait Members
Traits support the use of abstract methods in order to impose requirements upon the exhibiting class.
Exemplo #8 Express Requirements by Abstract Methods
<?php
trait Hello {
public function sayHelloWorld() {
echo 'Hello'.$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;
}
}
?>
Static Trait Members
Static variables can be referred to in trait methods, but cannot be defined by the trait. Traits can, however, define static methods for the exhibiting class.
Exemplo #9 Static Variables
<?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
?>
Exemplo #10 Static Methods
<?php
trait StaticExample {
public static function doSomething() {
return 'Doing something';
}
}
class Example {
use StaticExample;
}
Example::doSomething();
?>
Properties
Traits can also define properties.
Exemplo #11 Defining Properties
<?php
trait PropertiesTrait {
public $x = 1;
}
class PropertiesExample {
use PropertiesTrait;
}
$example = new PropertiesExample;
$example->x;
?>
If a trait defines a property then a class can not define a property with
the same name, otherwise an error is issued. It is an
E_STRICT if the class definition is compatible (same
visibility and initial value) or fatal error otherwise.
Exemplo #12 Conflict Resolution
<?php
trait PropertiesTrait {
public $same = true;
public $different = false;
}
class PropertiesExample {
use PropertiesTrait;
public $same = true; // Strict Standards
public $different = true; // Fatal error
}
?>
add a note
User Contributed Notes
Traits - [18 notes]
Safak Ozpinar / safakozpinar at gmail ¶
1 year ago
chris dot rutledge at gmail dot com ¶
1 year 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
t8 at AT pobox dot com ¶
9 months 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 $t->getVar(); // -> 'var'
?>
Serafim ¶
3 months ago
Another useful property of traits:
<?php
namespace Traits;
trait Properties{
public function __get($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? =)
?>
karolis at iwsolutions dot ie ¶
9 months 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";
?>
ryanhanekamp at yahoo dot com ¶
11 months 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.
ryan at derokorian dot com ¶
1 year 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 $bar->name;
greywire at gmail dot com ¶
1 year ago
The best way to understand what traits are and how to use them is to look at them for what they essentially are: language assisted copy and paste.
If you can copy and paste the code from one class to another (and we've all done this, even though we try not to because its code duplication) then you have a candidate for a trait.
Jason dot Hofer dot deletify dot this dot part at gmail dot com ¶
1 year ago
A (somewhat) practical example of trait usage.
Without traits:
<?php
class Controller {
/* Controller-specific methods defined here. */
}
class AdminController extends Controller {
/* Controller-specific methods inherited from Controller. */
/* Admin-specific methods defined here. */
}
class CrudController extends Controller {
/* Controller-specific methods inherited from Controller. */
/* CRUD-specific methods defined here. */
}
class AdminCrudController extends CrudController {
/* Controller-specific methods inherited from Controller. */
/* CRUD-specific methods inherited from CrudController. */
/* (!!!) Admin-specific methods copied and pasted from AdminController. */
}
?>
With traits:
<?php
class Controller {
/* Controller-specific methods defined here. */
}
class AdminController extends Controller {
/* Controller-specific methods inherited from Controller. */
/* Admin-specific methods defined here. */
}
trait CrudControllerTrait {
/* CRUD-specific methods defined here. */
}
class AdminCrudController extends AdminController {
use CrudControllerTrait;
/* Controller-specific methods inherited from Controller. */
/* Admin-specific methods inherited from AdminController. */
/* CRUD-specific methods defined by CrudControllerTrait. */
}
?>
anthony bishopric ¶
1 year ago
The magic method __call works as expected using traits.
<?php
trait Call_Helper{
public function __call($name, $args){
return count($args);
}
}
class Foo{
use Call_Helper;
}
$foo = new Foo();
echo $foo->go(1,2,3,4); // echoes 4
D. Marti ¶
6 months 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>';
?>
Anonymous ¶
1 year ago
Traits can not implement interfaces.
(should be obvious, but tested is tested)
Edward ¶
1 year 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.
artur at webprojektant dot pl ¶
7 months ago
Trait can not have the same name as class because it will show: Fatal error: Cannot redeclare class
dario dot masamune at gmail dot com ¶
8 months ago
Just in case someone was wondering, traits can be inside namespaces too! Cool!!
syzer3 at gmail dot com ¶
5 days 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 $theHello -> getHello();
//one may just use
echo HelloWorld:make() -> getHello();
jan ¶
1 month ago
Hi! Just a quick solution to use class-identical static property. I use it to store SQL descriptions, which is always same for the same class, but may change for an extended class.
<?php
interface hasO{ // just for forcing basic functionalities
static function O($use_as);
function myObj($append = "nothing");
function inc();
static function getName();
}
class O{ // the target class to access
var $val, $num = 0;
function setVAl($val){$this->val = $val;}
function inc(){$this->num++;}
function prt($append){echo "hello, i'm {$this->val} with number: {$this->num} and append a string: {$append}<br>"; }
}
trait T{ // the trait to access O
private static $objs = [];
private static $preference = [];
static function setPreference($class){
self::$preference[get_called_class()] = $class; // we can hack even polymorphism
}
static function O($use_as = null){
/* we use $use_as, preference or the current calling class in this order. */
$cc = ($use_as ? $use_as : (($cc2 = @self::$preference[get_called_class()])!= null ? $cc2 : get_called_class()));
if (!@self::$objs[$cc]){ // you have to use 'self::' to access a private method.
self::$objs[$cc] = new O();
self::$objs[$cc]->setVal(static::getName()); // but you can use 'static::' to access class method.
}
return self::$objs[$cc];
}
}
class A implements hasO{ // A is independent from the other classes
use T;
static function getName() {return 'A';}
function myObj($append = "i'm A",$use_as = null){
if (!$append && $append !== false) $append = "i'm ".get_called_class();
self::O($use_as)->prt($append);
}
function inc(){self::O()->inc();}
}
class B implements hasO{
use T;
function myObj($append = null){
if (!$append && $append !== false) $append = "i'm ".get_called_class();
static::O()->prt($append);
}
function inc(){static::O()->inc();}
static function getName() {return get_called_class();}
}
class C extends B{} // not relevant inheritence.
class D extends B{
use T; // you won't get errors if you accidently reuse the same trait
static function getName() {return 'a child of B ';} // we can use current object static methods, so inheritence is intact
function inc(){
static::O()->inc(); // both self::O and static::O is usable to preserve further inherits
self::O()->inc();
}
}
class E extends B{
const CLSS = 'E';
function myObj($append="EEEE!", $use_as = null){
if (!$append && $append !== false) $append = "i'm ".get_called_class();
self::O($use_as)->prt($append);
}
}
$a = new A;$b = new B;$c = new C;$d = new D;$e = new E; // create all objects...
$b->myObj(); $b->inc(); $b->myObj();
$c->myObj(); $c->inc(); $c->myObj(); // C comes before A, so C's object is already instantized before A tries to access it
$a->myObj(); $a->inc(); $a->myObj();
$a->myObj(null,'C'); // this isn't works, because it's protected private
$d->myObj(); $d->inc(); $d->myObj();
$e->myObj(); $e->inc(); $e->myObj("i'm E again");
$e->myObj(0,'C'); // but this IS working, even if it's private NOT protected.
$e::setPreference('B'); // we want to morph to B
$e->myObj();
$e->inc(); // we incement B's object now as seen bellow
$e->myObj(); $b->myObj();
?>
farhad dot peb at gmail dot com ¶
1 year ago
<?php
trait first_trait
{
function first_function()
{
echo "From First Trait";
}
}
trait second_trait
{
function first_function()
{
echo "From Second Trait";
}
}
class first_class
{
use first_trait, second_trait
{
// This class will now call the method
// first function from first_trait only
first_trait::first_function insteadof second_trait;
// first_function of second_traits can be
// accessed with second_function
second_trait::first_function as second_function;
}
}
$obj = new first_class();
// Output: From First Trait
$obj->first_function();
// Output: From Second Trait
$obj->second_function();
?>
the iranian php programmer
writer: farhad zand
farhad.peb@gmail.com
php_engineer_bk@yahoo.com