PHP5.4 Trait 使用

今天接触了laravel框架, 发现里面使用了很多的trait, 引发了我写这博文的冲动。

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

PS: 参考Shameer C’s Blog