awesomePHP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

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']);});