caffe中有許多的layer,在net中建立連線layer是通過工廠模式的方式建立，而不是每一個new然後連線。在net.cpp中建立layer方式如下：

layers_.push_back(LayerRegistry<Dtype>::CreateLayer(layer_param));

下面簡要分析下layer_factory

template<typename Dtype>
class LayerRegistry{
public:
    // 函式指標Creator，返回Layer<Dtype>指標
    typedef shared_ptr<
 
Layer<Dtype>> (*Creator)(const LayerParameter&);
    typedef std::map<string, Creator> CreatorRegistry;

    static CreatorRegistry& Registry() {
        static CreatorRegistry* g_registry_ = new CreatorRegistry();
        return *g_registry_;
    }

    // Adds a creator.
    static
 
 void AddCreator(const string& type, Creator creator) {
        CreatorRegistry& registry = Registry();
        LOG(INFO) << "AddCreator: " << type;
        registry[type] = creator;
    }

    // Get a layer using a LayerParameter.
    static shared_ptr<Layer<Dtype> > CreateLayer
 
(const LayerParameter& param) {

        const string& type = param.type();
        CreatorRegistry& registry = Registry();

        CHECK_EQ(registry.count(type), 1) << "Unknown layer type: ";
        return registry[type](param);
    }
private:
    // Layer registry should never be instantiated
    // everything is done with its static variables.
    LayerRegistry() {}
};

結合巨集定義以及模板特化建立的對應的註冊類：

template <typename Dtype>
class LayerRegisterer {
public:
    LayerRegisterer(const string& type,
                  shared_ptr<Layer<Dtype>>(*creator)(const LayerParameter&))
    {
        LayerRegistry<Dtype>::AddCreator(type, creator);
    }
};

#define REGISTER_LAYER_CREATOR(type, creator)                                       \
  static LayerRegisterer<float> g_creator_f_##type(#type, creator<float>);     \
  static LayerRegisterer<double> g_creator_d_##type(#type, creator<double>)    \

#define REGISTER_LAYER_CLASS(type)                                                     \
  template <typename Dtype>                                                              \
  shared_ptr<Layer<Dtype> > Creator_##type##Layer(const LayerParameter& param) \
  {                                                                                            \
    return shared_ptr<Layer<Dtype> >(new type##Layer<Dtype>(param));              \
  }                                                                                            \
  REGISTER_LAYER_CREATOR(type, Creator_##type##Layer)
    
}

使用如下,例如輸入層：

INSTANTIATE_CLASS(InputLayer);
REGISTER_LAYER_CLASS(Input);