class Mail{public function send(){/*这里是如何发送邮件的代码*/}
}

class Register{private $_emailObj;public function doRegister(){/*这里是如何注册*/$this->_emailObj = new Mail();$this->_emailObj->send();//发送邮件
    }
}

include 'Mail.class.php';
include 'Register.class.php';
$reg = new Register();
$reg->doRegister();

interface Mail
{public function send();
}

class Email implements Mail()
{public function send(){//发送Email
    }
}

class SmsMail implements Mail()
{public function send(){//发送短信
    }
}

class Register
{private $_mailObj;public function __construct(Mail $mailObj){$this->_mailObj = $mailObj;}public function doRegister(){/*这里是如何注册*/$this->_mailObj->send();//发送信息
    }
}

/* 此处省略若干行 */
$reg = new Register();
$emailObj = new Email();
$smsObj = new SmsMail();$reg->doRegister($emailObj);//使用email发送
$reg->doRegister($smsObj);//使用短信发送
/* 你甚至可以发完邮件再发短信 */

/**
*    依赖注入类
*/
class Container{/***@var array 存储各个类的定义  以类的名称为键*/private $_definitions = array();/***@var array 存储各个类实例化需要的参数 以类的名称为键*/private $_params = array();/***@var array 存储各个类实例化的引用*/private $_reflections = array();/*** @var array 各个类依赖的类*/private $_dependencies = array();/*** 设置依赖* @param string $class 类、方法 名称* @param mixed $defination 类、方法的定义* @param array $params 类、方法初始化需要的参数*/public function set($class, $defination = array(), $params = array()){$this->_params[$class] = $params;$this->_definitions[$class] = $this->initDefinition($class, $defination);}/*** 获取实例* @param string $class 类、方法 名称* @param array $params 实例化需要的参数* @param array $properties 为实例配置的属性* @return mixed*/public function get($class, $params = array(), $properties = array()){if(!isset($this->_definitions[$class])){//如果重来没有声明过 则直接创建return $this->bulid($class, $params, $properties);}$defination = $this->_definitions[$class];if(is_callable($defination, true)){//如果声明是函数$params = $this->parseDependencies($this->mergeParams($class, $params));$obj = call_user_func($defination, $this, $params, $properties);}elseif(is_array($defination)){$originalClass = $defination['class'];unset($definition['class']);//difinition中除了'class'元素外 其他的都当做实例的属性处理$properties = array_merge((array)$definition, $properties);//合并该类、函数声明时的参数$params = $this->mergeParams($class, $params);if($originalClass === $class){//如果声明中的class的名称和关键字的名称相同 则直接生成对象$obj = $this->bulid($class, $params, $properties);}else{//如果不同则有可能为别名 则从容器中获取$obj = $this->get($originalClass, $params, $properties);}}elseif(is_object($defination)){//如果是个对象 直接返回return $defination;}else{throw new Exception($class . ' 声明错误!');}return $obj;}/*** 合并参数* @param string $class 类、函数 名称* @param array $params 参数* @return array*/protected function mergeParams($class, $params = array()){if(empty($this->_params[$class])){return $params;}if(empty($params)){return $this->_params;}$result = $this->_params[$class];foreach($params as $key => $value) {$result[$key] = $value;}return $result;}/*** 初始化声明* @param string $class 类、函数 名称* @param array $defination 类、函数的定义* @return mixed*/protected function initDefinition($class, $defination){if(empty($defination)){return array('class' => $class);}if(is_string($defination)){return array('class' => $defination);}if(is_callable($defination) || is_object($defination)){return $defination;}if(is_array($defination)){if(!isset($defination['class'])){$definition['class'] = $class;}return $defination;}throw new Exception($class. ' 声明错误');}/*** 创建类实例、函数* @param string $class 类、函数 名称* @param array $params 初始化时的参数* @param array $properties 属性* @return mixed*/protected function bulid($class, $params, $properties){list($reflection, $dependencies) = $this->getDependencies($class);foreach ((array)$params as $index => $param) {//依赖不仅有对象的依赖 还有普通参数的依赖$dependencies[$index] = $param;}$dependencies = $this->parseDependencies($dependencies, $reflection);$obj = $reflection->newInstanceArgs($dependencies);if(empty($properties)){return $obj;}foreach ((array)$properties as $name => $value) {$obj->$name = $value;}return $obj;}/*** 获取依赖* @param string $class 类、函数 名称* @return array*/protected function getDependencies($class){if(isset($this->_reflections[$class])){//如果已经实例化过 直接从缓存中获取return array($this->_reflections[$class], $this->_dependencies[$class]);}$dependencies = array();$ref = new ReflectionClass($class);//获取对象的实例$constructor = $ref->getConstructor();//获取对象的构造方法if($constructor !== null){//如果构造方法有参数foreach($constructor->getParameters() as $param) {//获取构造方法的参数if($param->isDefaultValueAvailable()){//如果是默认 直接取默认值$dependencies[] = $param->getDefaultValue();}else{//将构造函数中的参数实例化$temp = $param->getClass();$temp = ($temp === null ? null : $temp->getName());$temp = Instance::getInstance($temp);//这里使用Instance 类标示需要实例化 并且存储类的名字$dependencies[] = $temp;}}}$this->_reflections[$class] = $ref;$this->_dependencies[$class] = $dependencies;return array($ref, $dependencies);}/*** 解析依赖* @param array $dependencies 依赖数组* @param array $reflection 实例* @return array $dependencies*/protected function parseDependencies($dependencies, $reflection = null){foreach ((array)$dependencies as $index => $dependency) {if($dependency instanceof Instance){if ($dependency->id !== null) {$dependencies[$index] = $this->get($dependency->id);} elseif($reflection !== null) {$parameters = $reflection->getConstructor()->getParameters();$name = $parameters[$index]->getName();$class = $reflection->getName();throw new Exception('实例化类 ' . $class . ' 时缺少必要参数:' . $name);}   }}return $dependencies;}
}

class Instance{/*** @var 类唯一标示*/public $id;/*** 构造函数* @param string $id 类唯一ID* @return void*/public function __construct($id){$this->id = $id;}/*** 获取类的实例* @param string $id 类唯一ID* @return Object Instance*/public static function getInstance($id){return new self($id);}
}

class Base{/*** 魔术方法* @param string $name* @param string $value* @return void*/public function __set($name, $value){$this->{$name} = $value;}
}

class A extends Base{private $instanceB;public function __construct(B $instanceB){$this->instanceB = $instanceB;}public function test(){$this->instanceB->test();}
}

class B  extends Base{private $instanceC;public function __construct(C $instanceC){$this->instanceC = $instanceC;}public function test(){return $this->instanceC->test();}
}

class C  extends Base{public function test(){echo 'this is C!';}
}de

function autoload($className)
{include_once $className . '.class.php';
}
spl_autoload_register('autoload', true, true);
$container = new Container;$a = $container->get('A');
$a->test();//输出 'this is C!'

$container->set('foo', function($container, $params, $config){print_r($params);print_r($config);
});$container->get('foo', array('name' => 'foo'), array('key' => 'test'));

class Test
{public function mytest(){echo 'this is a test';}
}$container->set('testObj', new Test());$test = $container->get('testObj');
$test->mytest();