PHP5.4 Trait 使用详解编程语言

Trait 是个什么鬼

PHP Trait 是一个抽象类, 不能实例化, 简单理解就是将trait的代码复制, 粘贴到你使用trait的类中. 和接口对比, 还是有区别的
有这么个问题.

<?php 
class DbReader extends Mysqli 
{ 
} 
 
class FileReader extends SplFileObject 
{ 
}

DbReader, FileReader 都需要些公共方法, 假设都设计为单列模式, 两个类都需要getInstance方法, php不支持多继承, 怎么办?

<?php 
interface Singleton 
{ 
    public static function getInstance(); 
} 
 
class DbReader extends Mysqli implements Singleton 
{ 
    public static function getInstance(){ return "instanceOfDbReader";} 
} 
 
class FileReader extends SplFileObject implements Singleton 
{ 
    public static function getInstance(){ return "instanceOfFileReader";} 
}

是你想要的吗? 显然是NO

SO PHP特性 Trait

<?php 
trait Singleton 
{ 
    private static $instance; 
 
    public static function getInstance() { 
        if (!(self::$instance instanceof self)) { 
            self::$instance = new self; 
        } 
        return self::$instance; 
    } 
} 
 
class DbReader extends ArrayObject 
{ 
    use Singleton; 
} 
 
class  FileReader 
{ 
    use Singleton; 
} 
$a = DbReader::getInstance(); 
$b = FileReader::getInstance(); 
var_dump($a);  //object(DbReader) 
var_dump($b);  //object(FileReader)

是不是爽了!!!.

使用多个Trait

PHP Trait 是可以多个使用的

<?php 
trait Hello 
{ 
    function sayHello() { 
        echo "Hello"; 
    } 
} 
 
trait World 
{ 
    function sayWorld() { 
        echo "World"; 
    } 
} 
 
class MyWorld 
{ 
    use Hello, World; 
} 
 
$world = new MyWorld(); 
echo $world->sayHello() . " " . $world->sayWorld(); //Hello World

是不是很方便!!!

Trait 组装 Trait

多个Trait可以组装成一个Trait

<?php 
trait Hello 
{ 
    function sayHello() { 
        echo "Hello"; 
    } 
} 
 
trait World 
{ 
    function sayWorld() { 
        echo "World"; 
    } 
} 
trait HelloWorld 
{ 
    use Hello, World; 
} 
 
class MyWorld 
{ 
    use HelloWorld; 
} 
 
$world = new MyWorld(); 
echo $world->sayHello() . " " . $world->sayWorld(); //Hello World

Trait 优先级

Trait中的方法重写继承父类的方法.   
当前类中方法复写trait中的方法   
 
<?php 
trait Hello 
{ 
    function sayHello() { 
        return "Hello"; 
    } 
 
    function sayWorld() { 
        return "Trait World"; 
    } 
 
    function sayHelloWorld() { 
        echo $this->sayHello() . " " . $this->sayWorld(); 
    } 
 
    function sayBaseWorld() { 
        echo $this->sayHello() . " " . parent::sayWorld(); 
    } 
} 
 
class Base 
{ 
    function sayWorld(){ 
        return "Base World"; 
    } 
} 
 
class HelloWorld extends Base 
{ 
    use Hello; 
    function sayWorld() { 
        return "World"; 
    } 
} 
 
$h =  new HelloWorld(); 
$h->sayHelloWorld(); // Hello World 
$h->sayBaseWorld(); // Hello Base World

解决Trait冲突

<?php 
trait Game 
{ 
    function play() { 
        echo "Playing a game"; 
    } 
} 
 
trait Music 
{ 
    function play() { 
        echo "Playing music"; 
    } 
} 
 
class Player 
{ 
    use Game, Music; 
} 
 
$player = new Player(); 
$player->play(); // Fatal Error 
 
// resolve one 
class Player 
{ 
    use Game, Music { 
        Music::play insteadof Game; 
    } 
} 
 
$player = new Player(); 
$player->play(); //Playing music 
 
// resolve two 
class Player 
{ 
    use Game, Music { 
        Game::play as gamePlay; 
        Music::play insteadof Game; 
    } 
} 
 
$player = new Player(); 
$player->play(); //Playing music 
$player->gamePlay(); //Playing a game

使用PHP Reflection类 ReflectionClass::getTraits() 获取类使用的traits. ReflectionClass::getTraitNames() 获取类中trait名称 ReflectionClass::isTrait() 此类是否是trait

其他特性

trait中的 protected, private 可以随便访问

<?php 
trait Message 
{ 
    private $message; 
 
    function alert() { 
        $this->define(); 
        echo $this->message; 
    } 
    abstract function define(); 
} 
 
class Messenger 
{ 
    use Message; 
    function define() { 
        $this->message = "Custom Message"; 
    } 
} 
 
$messenger = new Messenger; 
$messenger->alert(); //Custom Message

参考Shameer C’s Blog