awesome PHP之依赖注入容器pimple

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

<?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。

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：

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']);
});