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
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<?php/* * 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。
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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：
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require __DIR__ . '/vendor/autoload.php'; // define some services$container['session_storage'] = function ($c) { return new $c['session_storage_class']($c['cookie_name']);};$container['session'] = function ($c) { return new Session($c['session_storage']);};// get the session object$session = $container['session'];$container['session'] = $container->factory(function ($c) { return new Session($c['session_storage']);});立即学习“PHP免费学习笔记（深入）”；
