依賴注入（Dependency Injection）又叫控制反轉（Inversion of Control）是一個重要的面向物件程式設計的法則來削減計算機程式的耦合問題，它能消除元件間的直接依賴關係，讓元件的開發更獨立，使用更靈活，在java框架中應用非常廣泛。在php中由於語言特性不能完全照搬java的那一套，但簡單的功能還是可以實現的。pimple就是php社群中比較流行的一種ioc容器。

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

pimple的優勢是簡單，就一個檔案

<?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類就繼承一個php陣列物件介面，在程式整個生命週期中，各種屬性、方法、物件、閉包都可以註冊其中，得易於php的陣列的hashtable實現，容器本身的查詢效率不算是太低。類似zf1中的Zend_Register或者Yii的委託代理形式，總體來說還是pimple直觀些。

pimple只是實現了一個容器的概念，關於依賴注入自動建立關聯物件的功能可以參照Laravel4和z2中的實現。一個例子程式碼：

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']);
});