factory.h

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#ifndef SINGA_UTILS_FACTORY_H_
#define SINGA_UTILS_FACTORY_H_

#include <functional>
#include <map>
#include <string>

#include "singa/utils/logging.h"
#define CreateInstance(SubClass, BaseClass) \
  [](void)->BaseClass* {return new SubClass();}

template<typename T, typename ID = std::string>
class Factory {
 public:
  static void Register(const ID& id,
                       const std::function<T*(void)>& creator) {
    Registry* reg = GetRegistry();
    // CHECK(reg->find(id) == reg->end())
    //  << "The id " << id << " has been registered";
    (*reg)[id] = creator;
  }

  static T* Create(const ID& id) {
    Registry* reg = GetRegistry();
    CHECK(reg->find(id) != reg->end())
      << "The creation function for " << id << " has not been registered";
    return (*reg)[id]();
  }

  static const std::vector<ID> GetIDs() {
    std::vector<ID> keys;
    for (const auto entry : *GetRegistry())
      keys.push_back(entry.first);
    return keys;
  }

 private:
  // Map that stores the registered creation functions
  typedef std::map<ID, std::function<T*(void)>> Registry;
  static Registry* GetRegistry() {
    static Registry reg;
    return &reg;
  }
};

template<typename Base, typename Sub, typename ID = std::string>
class Registra {
 public:
  Registra(const ID& id) {
    Factory<Base, ID>::Register(id, [](void) { return new Sub(); });
  }
};
#endif  // SINGA_UTILS_FACTORY_H_