什么是容器

在開發過程中，經常會用到的一個概念就是依賴注入。我們借助依懶注入來解耦代碼，選擇性的按需加載服務，而這些通常都是借助容器來實現。

容器實現對對象的統一管理，并且確保對象實例的唯一性

容器可以很輕易的找到有很多實現示例，如 PHP-DI 、 YII-DI 等各種實現，通常他們要么大而全，要么高度適配特定業務，與實際需要存在沖突。

出于需要，我們自己造一個輕量級的輪子，為了保持規范，我們基于 PSR-11 來實現。

PSR-11

PSR 是 php-fig 提供的標準化建議，雖然不是官方組織，但是得到廣泛認可。PSR-11 提供了容器接口。它包含 ContainerInterface 和 兩個異常接口，并提供使用建議。

/** * 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 $id Identifier of the entry to look for. * @throws NotFoundExceptionInterface No entry was found for **this** identifier. * @throws ContainerExceptionInterface Error while retrieving the entry. * @return mixed Entry. html' target='_blank'>public function get($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);}

實現示例

我們先來實現接口中要求的兩個方法

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]); }

實際我們容器中注入的對象是多種多樣的，所以我們單獨抽出實例化方法。

 protected function make($name) if (isset($this- resolvedEntries[$name])) { return $this- resolvedEntries[$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; * 獲取構造類相關參數的依賴 * @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; }

如你所見，到目前為止我們只實現了從容器中取出實例，從哪里去提供實例定義呢，所以我們還需要提供一個方法.

 /** * @param string $id * @param string | array | callable $concrete * @throws ContainerException public function injection($id, $concrete) if (!is_string($id)) { throw new /InvalidArgumentException(sprintf( The id parameter must be of type string, %s given , is_object($id) ? get_class($id) : gettype($id) if (is_array($concrete) !isset($concrete[ class ])) { throw new ContainerException( 數組必須包含類定義  $this- definitions[$id] = $concrete; }        
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