原文地址：http://blog.csdn.net/wzllai/article/details/24485245

依赖注入（Dependency Injection）又叫控制反转（Inversion of Control）是一个重要的面向对象编程的法则来削减计算机程序的耦合问题，它能消除组件间的直接依赖关系，让组件的开发更独立，使用更灵活，在java框架中应用非常广泛。在php中由于语言特性不能完全照搬java的那一套，但简单的功能还是可以实现的。pimple就是php社区中比较流行的一种ioc容器。

可以用composer添加 require  "pimple/pimple": "1.*"

pimple的优势是简单，就一个文件

/* 
 * This file is part of Pimple. 
 * 
 * Copyright (c) 2009 Fabien Potencier 
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy 
 * of this software and associated documentation files (the "Software"), to deal 
 * in the Software without restriction, including without limitation the rights 
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
 * copies of the Software, and to permit persons to whom the Software is furnished 
 * to do so, subject to the following conditions: 
 * 
 * The above copyright notice and this permission notice shall be included in all 
 * copies or substantial portions of the Software. 
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 
 * THE SOFTWARE. 
 */  
  
/** 
 * Pimple main class. 
 * 
 * @package pimple 
 * @author  Fabien Potencier 
 */  
class Pimple implements \ArrayAccess  
{  
    private $values = array();  
    private $factories;  
    private $protected;  
    private $frozen = array();  
    private $raw = array();  
    private $keys = array();  
  
    /** 
     * Instantiate the container. 
     * 
     * Objects and parameters can be passed as argument to the constructor. 
     * 
     * @param array $values The parameters or objects. 
     */  
    public function __construct(array $values = array())  
    {  
        $this->factories = new \SplObjectStorage();  
        $this->protected = new \SplObjectStorage();  
  
        foreach ($values as $key => $value) {  
            $this->offsetSet($key, $value);  
        }  
    }  
  
    /** 
     * Sets a parameter or an object. 
     * 
     * Objects must be defined as Closures. 
     * 
     * Allowing any PHP callable leads to difficult to debug problems 
     * as function names (strings) are callable (creating a function with 
     * the same name as an existing parameter would break your container). 
     * 
     * @param  string           $id    The unique identifier for the parameter or object 
     * @param  mixed            $value The value of the parameter or a closure to define an object 
     * @throws RuntimeException Prevent override of a frozen service 
     */  
    public function offsetSet($id, $value)  
    {  
        if (isset($this->frozen[$id])) {  
            throw new \RuntimeException(sprintf('Cannot override frozen service "%s".', $id));  
        }  
  
        $this->values[$id] = $value;  
        $this->keys[$id] = true;  
    }  
  
    /** 
     * Gets a parameter or an object. 
     * 
     * @param string $id The unique identifier for the parameter or object 
     * 
     * @return mixed The value of the parameter or an object 
     * 
     * @throws InvalidArgumentException if the identifier is not defined 
     */  
    public function offsetGet($id)  
    {  
        if (!isset($this->keys[$id])) {  
            throw new \InvalidArgumentException(sprintf('Identifier "%s" is not defined.', $id));  
        }  
  
        if (  
            isset($this->raw[$id])  
            || !is_object($this->values[$id])  
            || isset($this->protected[$this->values[$id]])  
            || !method_exists($this->values[$id], '__invoke')  
        ) {  
            return $this->values[$id];  
        }  
  
        if (isset($this->factories[$this->values[$id]])) {  
            return $this->values[$id]($this);  
        }  
  
        $this->frozen[$id] = true;  
        $this->raw[$id] = $this->values[$id];  
  
        return $this->values[$id] = $this->values[$id]($this);  
    }  
  
    /** 
     * Checks if a parameter or an object is set. 
     * 
     * @param string $id The unique identifier for the parameter or object 
     * 
     * @return Boolean 
     */  
    public function offsetExists($id)  
    {  
        return isset($this->keys[$id]);  
    }  
  
    /** 
     * Unsets a parameter or an object. 
     * 
     * @param string $id The unique identifier for the parameter or object 
     */  
    public function offsetUnset($id)  
    {  
        if (isset($this->keys[$id])) {  
            if (is_object($this->values[$id])) {  
                unset($this->factories[$this->values[$id]], $this->protected[$this->values[$id]]);  
            }  
  
            unset($this->values[$id], $this->frozen[$id], $this->raw[$id], $this->keys[$id]);  
        }  
    }  
  
    /** 
     * Marks a callable as being a factory service. 
     * 
     * @param callable $callable A service definition to be used as a factory 
     * 
     * @return callable The passed callable 
     * 
     * @throws InvalidArgumentException Service definition has to be a closure of an invokable object 
     */  
    public function factory($callable)  
    {  
        if (!is_object($callable) || !method_exists($callable, '__invoke')) {  
            throw new \InvalidArgumentException('Service definition is not a Closure or invokable object.');  
        }  
  
        $this->factories->attach($callable);  
  
        return $callable;  
    }  
  
    /** 
     * Protects a callable from being interpreted as a service. 
     * 
     * This is useful when you want to store a callable as a parameter. 
     * 
     * @param callable $callable A callable to protect from being evaluated 
     * 
     * @return callable The passed callable 
     * 
     * @throws InvalidArgumentException Service definition has to be a closure of an invokable object 
     */  
    public function protect($callable)  
    {  
        if (!is_object($callable) || !method_exists($callable, '__invoke')) {  
            throw new \InvalidArgumentException('Callable is not a Closure or invokable object.');  
        }  
  
        $this->protected->attach($callable);  
  
        return $callable;  
    }  
  
    /** 
     * Gets a parameter or the closure defining an object. 
     * 
     * @param string $id The unique identifier for the parameter or object 
     * 
     * @return mixed The value of the parameter or the closure defining an object 
     * 
     * @throws InvalidArgumentException if the identifier is not defined 
     */  
    public function raw($id)  
    {  
        if (!isset($this->keys[$id])) {  
            throw new \InvalidArgumentException(sprintf('Identifier "%s" is not defined.', $id));  
        }  
  
        if (isset($this->raw[$id])) {  
            return $this->raw[$id];  
        }  
  
        return $this->values[$id];  
    }  
  
    /** 
     * Extends an object definition. 
     * 
     * Useful when you want to extend an existing object definition, 
     * without necessarily loading that object. 
     * 
     * @param string   $id       The unique identifier for the object 
     * @param callable $callable A service definition to extend the original 
     * 
     * @return callable The wrapped callable 
     * 
     * @throws InvalidArgumentException if the identifier is not defined or not a service definition 
     */  
    public function extend($id, $callable)  
    {  
        if (!isset($this->keys[$id])) {  
            throw new \InvalidArgumentException(sprintf('Identifier "%s" is not defined.', $id));  
        }  
  
        if (!is_object($this->values[$id]) || !method_exists($this->values[$id], '__invoke')) {  
            throw new \InvalidArgumentException(sprintf('Identifier "%s" does not contain an object definition.', $id));  
        }  
  
        if (!is_object($callable) || !method_exists($callable, '__invoke')) {  
            throw new \InvalidArgumentException('Extension service definition is not a Closure or invokable object.');  
        }  
  
        $factory = $this->values[$id];  
  
        $extended = function ($c) use ($callable, $factory) {  
            return $callable($factory($c), $c);  
        };  
  
        if (isset($this->factories[$factory])) {  
            $this->factories->detach($factory);  
            $this->factories->attach($extended);  
        }  
  
        return $this[$id] = $extended;  
    }  
  
    /** 
     * Returns all defined value names. 
     * 
     * @return array An array of value names 
     */  
    public function keys()  
    {  
        return array_keys($this->values);  
    }  
}  

pimple类就继承一个php数组对象接口，在程序整个生命周期中，各种属性、方法、对象、闭包都可以注册其中，得易于php的数组的hashtable实现，容器本身的查询效率不算是太低。类似zf1中的Zend_Register或者Yii的委托代理形式，总体来说还是pimple直观些。

pimple只是实现了一个容器的概念，关于依赖注入自动创建关联对象的功能可以参照Laravel4和z2中的实现。一个例子代码:

class A{

}
class B{
	public function __construct(A a){}
}
class C{
	public function __construct(B b){}
	public function dosomething(){}
}
$container = new pimple;

$container->a = function () {
	return new A();
};
$c->b = function ($c) {
	return new B($c->a);
};
$c->c = function ($c) {
	return new C($c->b);
};

// 从容器中取得Foo
$foo = $c->foo;
$foo->doSomething();
// Bim::doSomething|Bar::doSomething|Foo::doSomething
// 依赖注入的核心就是将对象和类的依赖关系注册到容器中。