结构体套结构体指针--有什么黑魔法么

在看 k8s 源代码时候，有这么一段代码，其中 Complete()方法， 看注释是可以填充没有设置的字段，填充字段需要这么套娃么.

CompletedConfig --》 指针 completedConfig --》 Config 指针

// Config is the main context object for the controller manager.
type Config struct {
	ComponentConfig kubectrlmgrconfig.KubeControllerManagerConfiguration

	SecureServing *apiserver.SecureServingInfo
	// LoopbackClientConfig is a config for a privileged loopback connection
	LoopbackClientConfig *restclient.Config

	// TODO: remove deprecated insecure serving
	InsecureServing *apiserver.DeprecatedInsecureServingInfo
	Authentication  apiserver.AuthenticationInfo
	Authorization   apiserver.AuthorizationInfo

	// the general kube client
	Client *clientset.Clientset

	// the client only used for leader election
	LeaderElectionClient *clientset.Clientset

	// the rest config for the master
	Kubeconfig *restclient.Config

	// the event sink
	EventRecorder record.EventRecorder
}

type completedConfig struct {
	*Config
}

// CompletedConfig same as Config, just to swap private object.
type CompletedConfig struct {
	// Embed a private pointer that cannot be instantiated outside of this package.
	*completedConfig
}

// Complete fills in any fields not set that are required to have valid data. It's mutating the receiver.
func (c *Config) Complete() *CompletedConfig {
	cc := completedConfig{c}

	apiserver.AuthorizeClientBearerToken(c.LoopbackClientConfig, &c.Authentication, &c.Authorization)

	return &CompletedConfig{&cc}
}