factory.h

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//
// Copyright (c) 2018, University of Edinburgh
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#ifndef EXOTICA_CORE_FACTORY_H_
#define EXOTICA_CORE_FACTORY_H_
 
#include <map>
#include <memory>
#include <typeinfo>
 
#include <exotica_core/object.h>
#include <exotica_core/tools.h>
 
#include <pluginlib/class_list_macros.h>
 
#define EXOTICA_CORE_REGISTER(BASE, TYPE, DERIV)                                                                                         \
    static exotica::Registrar<BASE> EX_UNIQ(object_registrar_, __LINE__)("exotica/" TYPE, []() -> BASE* { return new DERIV(); }, #BASE); \
    PLUGINLIB_EXPORT_CLASS(DERIV, BASE)
 
#define EXOTICA_CORE_REGISTER_CORE(BASE, TYPE, DERIV) static exotica::Registrar<BASE> EX_UNIQ(object_registrar_, __LINE__)("exotica/" TYPE, []() -> BASE* { return new DERIV(); }, #BASE);
 
namespace exotica
{
template <typename BaseClass>
class Registrar;
 
template <class BaseClass>
class Factory : public Object
{
public:
    friend class Registrar<BaseClass>;
 
    static Factory<BaseClass>& Instance(void)
    {
        static Factory<BaseClass> factory_;  
        return factory_;                     
    };
 
    void RegisterType(const std::string& type, BaseClass* (*creator_function)())
    {
        if (type_registry_.find(type) == type_registry_.end())  
        {
            type_registry_[type] = creator_function;
        }
        else  // I.e. it exists, then cannot re-create it!
        {
            ThrowPretty("Trying to register already existing type '" << type << "'!");
        }
    }
 
    std::shared_ptr<BaseClass> CreateInstance(const std::string& type)
    {
        auto it = type_registry_.find(type);  // Attempt to find it
        if (it != type_registry_.end())       // If exists
        {
            return std::shared_ptr<BaseClass>(it->second());
        }
        else
        {
            ThrowPretty("This factory does not recognize type '" << type << "' (" + base_type_ + ")");
        }
    }
 
    std::vector<std::string> GetDeclaredClasses()
    {
        std::vector<std::string> DeclaredClasses;
        for (auto it = type_registry_.begin(); it != type_registry_.end(); ++it)
        {
            DeclaredClasses.push_back(it->first);
        }
        return DeclaredClasses;
    }
 
private:
    inline explicit Factory<BaseClass>()
    {
    }
 
    std::map<std::string, BaseClass* (*)()> type_registry_;
    std::string base_type_;
};
 
template <typename BaseClass>
class Registrar
{
public:
    Registrar(const std::string& name, BaseClass* (*creator)(), const std::string& base_type)
    {
        Factory<BaseClass>::Instance().base_type_ = base_type;
        Factory<BaseClass>::Instance().RegisterType(name, creator);
    }
};
}  // namespace exotica
 
#endif  // EXOTICA_CORE_FACTORY_H_