详解如何实现Laravel的服务容器的方法示例(4)

class ParametersContainer extends InjectionContainer
{
  // 获取服务
  public function make($name, array $parameters = [])
  {
    if (isset($this->instances[$name])) {
      return $this->instances[$name];
    }
    if (isset($this->bindings[$name])) {
      // 执行回调函数并返回
      $instance = call_user_func($this->bindings[$name]['callback']);

      if ($this->bindings[$name]['shared']) {
        // 标记为单例时，存储到服务中
        $this->instances[$name] = $instance;
      }
    } else {
      // 使用build方法构建此类
      $instance = $this->build($name, $parameters);
    }

    return $instance;
  }

  // 构建一个类，并自动注入服务
  public function build($class, array $parameters = [])
  {
    $reflector = new ReflectionClass($class);

    $constructor = $reflector->getConstructor();

    if (is_null($constructor)) {
      // 没有构造函数，直接new
      return new $class();
    }

    $dependencies = [];

    // 获取构造函数所需的参数
    foreach ($constructor->getParameters() as $dependency) {

      if (isset($parameters[$dependency->getName()])) {
        // 先从自定义参数中查找
        $dependencies[] = $parameters[$dependency->getName()];
        continue;
      }

      if (is_null($dependency->getClass())) {
        // 参数类型不是类或接口时，无法从容器中获取依赖
        if ($dependency->isDefaultValueAvailable()) {
          // 查找默认值，如果有就使用默认值
          $dependencies[] = $dependency->getDefaultValue();
        } else {
          // 无法提供类所依赖的参数
          throw new Exception('找不到依赖参数：' . $dependency->getName());
        }
      } else {
        // 参数类型是类时，就用make方法构建该类
        $dependencies[] = $this->make($dependency->getClass()->name);
      }
    }

    return $reflector->newInstanceArgs($dependencies);
  }
}

// ----------- ↓↓↓↓示例代码↓↓↓↓ ----------- //

class Redis
{
}

class Cache
{
  protected $redis;

  protected $name;

  protected $default;

  // 构造函数中依赖Redis服务和name参数，name的类型不是类，无法从容器中查找
  public function __construct(Redis $redis, $name, $default = '默认值')
  {
    $this->redis = $redis;
    $this->name = $name;
    $this->default = $default;
  }
}

$container = new ParametersContainer();
// 绑定Redis服务
$container->singleton(Redis::class, function () {
  return new Redis();
});
// 构建Cache类
$cache = $container->make(Cache::class, ['name' => 'test']);
var_dump($cache);