PHP实现一个轻量级容器的方法

什么是容器

在开发过程中，经常会用到的一个概率就是依赖注入。我们借助依懒注入来解耦代码，选择性的按需加载服务，而这些通常都是借助容器来实现。

容器实现对类的统一管理，并且确保对象实例的唯一性

常用的容器网上有很多，如PHP-DI 、 YII-DI 等各种实现，通常他们要么大而全，要么高度适配特定业务，与实际需要存在冲突。

出于需要，我们自己造一个轻量级的轮子，为了保持规范，我们基于PSR-11 来实现。

PSR-11

PSR 是 php-fig 提供的标准建议，虽然不是官方组织，但是得到广泛认可。PSR-11 提供了容器接口。他包含 ContainerInterface 和 两个异常接口，提供使用建议。

  /**   * Describes the interface of a container that exposes methods to read its entries.   */  interface ContainerInterface  {    /**     * Finds an entry of the container by its identifier and returns it.     *     * @param string $id Identifier of the entry to look for.     *     * @throws NotFoundExceptionInterface No entry was found for **this** identifier.     * @throws ContainerExceptionInterface Error while retrieving the entry.     *     * @return mixed Entry.     */    public function get($id);      /**     * Returns true if the container can return an entry for the given identifier.     * Returns false otherwise.     *     * `has($id)` returning true does not mean that `get($id)` will not throw an exception.     * It does however mean that `get($id)` will not throw a `NotFoundExceptionInterface`.     *     * @param string $id Identifier of the entry to look for.     *     * @return bool     */    public function has($id);  }

实现示例

我们先来实现接口中要求的两个方法

  abstract class AbstractContainer implements ContainerInterface  {      protected $resolvedEntries = [];      /**     * @var array     */    protected $definitions = [];      public function __construct($definitions = [])    {      foreach ($definitions as $id => $definition) {        $this->injection($id, $definition);      }    }      public function get($id)    {        if (!$this->has($id)) {        throw new NotFoundException("No entry or class found for {$id}");      }        $instance = $this->make($id);        return $instance;    }      public function has($id)    {      return isset($this->definitions[$id]);    }

实际我们容器中注入的对象是多种多样的，所以我们单独抽出实例化方法。

  public function make($name)    {      if (!is_string($name)) {        throw new InvalidArgumentException(sprintf(          'The name parameter must be of type string, %s given',          is_object($name) ? get_class($name) : gettype($name)        ));      }        if (isset($this->resolvedEntries[$name])) {        return $this->resolvedEntries[$name];      }        if (!$this->has($name)) {        throw new NotFoundException("No entry or class found for {$name}");      }        $definition = $this->definitions[$name];      $params = [];      if (is_array($definition) && isset($definition['class'])) {        $params = $definition;        $definition = $definition['class'];        unset($params['class']);      }        $object = $this->reflector($definition, $params);        return $this->resolvedEntries[$name] = $object;    }      public function reflector($concrete, array $params = [])    {      if ($concrete instanceof Closure) {        return $concrete($params);      } elseif (is_string($concrete)) {        $reflection = new ReflectionClass($concrete);        $dependencies = $this->getDependencies($reflection);        foreach ($params as $index => $value) {          $dependencies[$index] = $value;        }        return $reflection->newInstanceArgs($dependencies);      } elseif (is_object($concrete)) {        return $concrete;      }    }      /**     * @param ReflectionClass $reflection     * @return array     */    private function getDependencies($reflection)    {      $dependencies = [];      $constructor = $reflection->getConstructor();      if ($constructor !== null) {        $parameters = $constructor->getParameters();        $dependencies = $this->getParametersByDependencies($parameters);      }        return $dependencies;    }      /**     *     * 获取构造类相关参数的依赖     * @param array $dependencies     * @return array $parameters     * */    private function getParametersByDependencies(array $dependencies)    {      $parameters = [];      foreach ($dependencies as $param) {        if ($param->getClass()) {          $paramName = $param->getClass()->name;          $paramObject = $this->reflector($paramName);          $parameters[] = $paramObject;        } elseif ($param->isArray()) {          if ($param->isDefaultValueAvailable()) {            $parameters[] = $param->getDefaultValue();          } else {            $parameters[] = [];          }        } elseif ($param->isCallable()) {          if ($param->isDefaultValueAvailable()) {            $parameters[] = $param->getDefaultValue();          } else {            $parameters[] = function ($arg) {            };          }        } else {          if ($param->isDefaultValueAvailable()) {            $parameters[] = $param->getDefaultValue();          } else {            if ($param->allowsNull()) {              $parameters[] = null;            } else {              $parameters[] = false;            }          }        }      }      return $parameters;    }

如你所见，到目前为止我们只实现了从容器中取出实例，从哪里去提供实例定义呢，所以我们还需要提供一个方水法

  /**     * @param string $id     * @param string | array | callable $concrete     * @throws ContainerException     */    public function injection($id, $concrete)    {      if (is_array($concrete) && !isset($concrete['class'])) {        throw new ContainerException('数组必须包含类定义');      }        $this->definitions[$id] = $concrete;    }

只有这样吗？对的，有了这些操作我们已经有一个完整的容器了，插箱即用。

不过为了使用方便，我们可以再提供一些便捷的方法，比如数组式访问。

  class Container extends AbstractContainer implements ArrayAccess  {      public function offsetExists($offset)    {      return $this->has($offset);    }      public function offsetGet($offset)    {      return $this->get($offset);    }      public function offsetSet($offset, $value)    {      return $this->injection($offset, $value);    }      public function offsetUnset($offset)    {      unset($this->resolvedEntries[$offset]);      unset($this->definitions[$offset]);    }  }

这样我们就拥有了一个功能丰富，使用方便的轻量级容器了，赶快整合到你的项目中去吧。