Factory関数を複数登録できるようにした。

base.hh

#ifndef BASE_HH_INCLUDED
#define BASE_HH_INCLUDED 1

struct Base
{
  virtual const char *ClassName() const
  {
    return "Base";
  }
};

#endif // !defined(BASE_HH_INCLUDED)

base_factory_registry.hh

#ifndef BASE_FACTORY_REGISTRY_HH_INCLUDED
#define BASE_FACTORY_REGISTRY_HH_INCLUDED 1

#include <cstddef>
#include "base.hh"
#include <iostream>

class BaseFactoryRegistry
{
public:
  BaseFactoryRegistry()
    : count_(0)
  {
  }
  void RegisterFactory(Base *(*factory)())
  {
    factories_[count_] = factory;
    ++count_;
  }
  Base *NewBase(size_t n)
  {
    return (factories_[n])();
  }
  size_t Count() const
  {
    return count_;
  }
  static BaseFactoryRegistry *Instance()
  {
    static BaseFactoryRegistry instance;
    return &instance;
  }
private:
  Base *(*factories_[10])();
  size_t count_;
};

#define BASE_FACTORY_REGISTRATION(klass)				\
  struct BaseFactoryRegistration_##klass {				\
    BaseFactoryRegistration_##klass() {					\
      BaseFactoryRegistry::Instance()->RegisterFactory(New##klass);	\
    }									\
    static Base *New##klass() {						\
      return new klass;							\
    }									\
  };									\
  BaseFactoryRegistration_##klass base_factory_registration_##klass

#endif // !defined(BASE_FACTORY_REGISTRY_HH_INCLUDED)

derived.cc

#include "derived.hh"
#include "base_factory_registry.hh"

BASE_FACTORY_REGISTRATION(Derived);

derived.hh

#ifndef DERIVED_HH_INCLUDED
#define DERIVED_HH_INCLUDED

#include "base.hh"

struct Derived : public Base
{
  const char *ClassName() const
  {
    return "Derived";
  }
};

#endif // !defined(DERIVED_HH_INCLUDED)

derived2.cc

#include "derived2.hh"
#include "base_factory_registry.hh"

BASE_FACTORY_REGISTRATION(Derived2);

derived2.hh

#ifndef DERIVED2_HH_INCLUDED
#define DERIVED2_HH_INCLUDED

#include "base.hh"

struct Derived2 : public Base
{
  const char *ClassName() const
  {
    return "Derived2";
  }
};

#endif // !defined(DERIVED2_HH_INCLUDED)

derived3.cc

#include "derived3.hh"
#include "base_factory_registry.hh"

BASE_FACTORY_REGISTRATION(Derived3);

derived3.hh

#ifndef DERIVED3_HH_INCLUDED
#define DERIVED3_HH_INCLUDED

#include "base.hh"

struct Derived3 : public Base
{
  const char *ClassName() const
  {
    return "Derived3";
  }
};

#endif // !defined(DERIVED3_HH_INCLUDED)

main.cc

#include "base_factory_registry.hh"
#include <iostream>

int main()
{
  for (size_t i = 0; i < BaseFactoryRegistry::Instance()->Count(); ++i) {
    Base *base = BaseFactoryRegistry::Instance()->NewBase(i);
    std::cout << base->ClassName() << std::endl;
  }
  return 0;
}

Makefile

CXX = g++
CXXFLAGS = -Wall -Wextra -O2 -g
CPPFLAGS =
AR = ar
LD = g++
LDFLAGS =
LIBS =
RM = rm -f

all: ok ng

clean:
	$(RM) ok ng
	$(RM) libderived.a
	$(RM) main.o derived.o derived2.o derived3.o

ok: main.o derived.o derived2.o derived3.o
	$(LD) $(LDFLAGS) -o $@ main.o derived.o derived2.o derived3.o

ng: main.o libderived.a
	$(LD) $(LDFLAGS) -o $@ main.o -L. -lderived

main.o: main.cc base_factory_registry.hh
	$(CXX) $(CXXFLAGS) -o $@ -c $<

derived.o: derived.cc base.hh derived.hh base_factory_registry.hh
	$(CXX) $(CXXFLAGS) -o $@ -c $<

derived2.o: derived2.cc base.hh derived2.hh base_factory_registry.hh
	$(CXX) $(CXXFLAGS) -o $@ -c $<

derived3.o: derived3.cc base.hh derived3.hh base_factory_registry.hh
	$(CXX) $(CXXFLAGS) -o $@ -c $<

libderived.a: derived.o derived2.o derived3.o
	$(RM) $@; $(AR) crs $@ derived.o derived2.o derived3.o