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.
Example #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 turn override inherited methods.
Example #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();
?>
The above example will output:
Hello World!
Example #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();
?>
The above example will output:
Hello Universe!
Multiple Traits
Multiple Traits can be inserted into a class by listing them in the use statement, separated by commas.
Example #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();
?>
The above example will output:
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.
Example #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.
Example #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.
Example #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();
$o->sayWorld();
?>
The above example will output:
Hello World!
Abstract Trait Members
Traits support the use of abstract methods in order to impose requirements upon the exhibiting class.
Example #8 Express Requirements by Abstract Methods
<?php
trait Hello {
public function sayHelloWorld() {
echo 'Hello'.$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
Traits can define both static members and static methods.
Example #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
?>
Example #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.
Example #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.
Example #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
}
?>
- Введение
- Основы
- Свойства
- Константы классов
- Автоматическая загрузка классов
- Конструкторы и деструкторы
- Область видимости
- Наследование
- Оператор разрешения области видимости (::)
- Ключевое слово "static"
- Абстрактные классы
- Интерфейсы объектов
- Трейты
- Anonymous classes
- Перегрузка
- Итераторы объектов
- Магические методы
- Ключевое слово "final"
- Клонирование объектов
- Сравнение объектов
- Контроль типа
- Позднее статическое связывание
- Объекты и ссылки
- Сериализация объектов
- Журнал изменений ООП
Коментарии
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
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.
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.
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
?>
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;
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'
?>
Trait can not have the same name as class because it will show: Fatal error: Cannot redeclare classTraits 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>';
?>
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.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.
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.
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;
}
?>
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).
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!"; }
}
?>
(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.
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() )
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,
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
?>
/*
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";
}
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 (language.oop5.late-static-bindings).
<?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.
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
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::$_bar; // Prints: World World
Here is an example how to work with visiblity and conflicts.
<?php
trait A
{
private function smallTalk()
{
echo 'a';
}
private function bigTalk()
{
echo 'A';
}
}
trait B
{
private function smallTalk()
{
echo 'b';
}
private function bigTalk()
{
echo 'B';
}
}
trait C
{
public function smallTalk()
{
echo 'c';
}
public function bigTalk()
{
echo 'C';
}
}
class Talker
{
use A, B, C {
//visibility for methods that will be involved in conflict resolution
B::smallTalk as public;
A::bigTalk as public;
//conflict resolution
B::smallTalk insteadof A, C;
A::bigTalk insteadof B, C;
//aliases with visibility change
B::bigTalk as public Btalk;
A::smallTalk as public asmalltalk;
//aliases only, methods already defined as public
C::bigTalk as Ctalk;
C::smallTalk as cmallstalk;
}
}
(new Talker)->bigTalk();//A
(new Talker)->Btalk();//B
(new Talker)->Ctalk();//C
(new Talker)->asmalltalk();//a
(new Talker)->smallTalk();//b
(new Talker)->cmallstalk();//c
If you override a method which was defined by a trait, calling the parent method will also call the trait's override. Therefore if you need to derive from a class which has a trait, you can extend the class without losing the trait's functionality:
<?php
trait ExampleTrait
{
public function output()
{
parent::output();
echo "bar<br>";
}
}
class Foo
{
public function output()
{
echo "foo<br>";
}
}
class FooBar extends Foo
{
use ExampleTrait;
}
class FooBarBaz extends FooBar
{
use ExampleTrait;
public function output()
{
parent::output();
echo "baz";
}
}
(new FooBarBaz())->output();
?>
Output:
foo
bar
baz
I have not seen this specific use case:
"Wanting to preserve action of parent class method, the trait one calling ::parent & also the child class mehod action".
// Child class.
use SuperTrait {
initialize as initializeOr;
}
public function initialize(array &$element) {
...
$this->initializeOr($element);
}
// Trait.
public function initialize(array &$element) {
...
parent::initialize($element);
}
// Parent class.
public function initialize(array &$element) {
...
}