Although this is a C++ question, I am trying to use this with unreal engine ot create my own classes.
Here is the specifics:
- Consider a simple constructor in a class with two input arguments,
concreteclass(_1, _2). - I have a map for this instantiation, map ``.
- Also, these classes work with different datatypes
concreteclass(_1,_2)is different fromconcreteclass(_1,_2).
Now that my problem is described above here is what I try to do using boost::factory pattern, classes defined in a string map and datatypes defined in an enum.
First, there is a simple way to demonstrate how boost factory pattern can be used with constructor arguments, the following code nicely works:
// Factory which takes two arguments
struct base {
base(int alpha) : alpha(alpha) {}
virtual ~base() = default;
virtual void print() const = 0;
int alpha;
};
struct derived : public base {
derived(int alpha, int beta) : base(alpha), beta(beta) {}
void print() const override {
std::cout << alpha << " " << beta << std::endl;
}
int beta;
};
void TestBoostFactoryWithTwoArgs()
{
// Constructor factory with two input args
{
std::map<std::string, boost::function<base* (int&, int&)>> factories;
factories["derived"] = boost::bind(boost::factory<derived*>(), _1, _2);
int x = 42;
int y = 51;
std::unique_ptr<base> b{ factories.at("derived")(x,y) };
b->print();
}
// Factory with two initialized inputs args - binding of values not at run time
{
std::map<std::string, boost::function<base* ()>> factories;
factories["derived"] = boost::bind(boost::factory<derived*>(), 42, 51);
std::unique_ptr<base> b{ factories.at("derived")() };
b->print();
}
}
Now consider my code - SimpleClasses.h:
// Dummy base class - non template
class IBaseClass
{
public:
};
// Templatized Derived Base class
template <typename T>
class ConcreteClass : public IBaseClass
{
private:
std::shared_ptr<IBaseClass> m_leftArgument;
std::shared_ptr<IBaseClass> m_leftArgument;
public:
ConcreteClass(std::unique_ptr<IBaseClass>& leftArgument, std::unique_ptr<IBaseClass>& rightArgument)
{
m_leftArgument = leftArgument;
m_rightArgument = rightArgument;
};
virtual T DoSomething()
{
cout << "I did something in Concrete Base Class" << endl;
return T();
}; // This is the main reason for creating T
};
template <typename T>
class ConcreteClassA : ConcreteClass
{
};
template <typename T>
class ConcreteClassB : ConcreteClass
{
};
template <typename T>
class ConcreteClassC : ConcreteClass
{
};
Another File, ClassFactory.h :
#pragma once
#include "SimpleClasses.h"
#include <memory>
#include <map>
#include <boost/functional/overloaded_function.hpp>
#include <boost/functional/factory.hpp>
using namespace std;
// Add More class Keys here
namespace MyClassesNamespace { // These are all string keys
static const string CLASS_A = "specialclassA";
static const string CLASS_B = "specialclassB";
static const string CLASS_C = "specialclassC";
};
enum EMyDataTypes
{
INT8,
FLOAT8,
FLOAT16,
};
// This type def we keep for non templatized base class constructor
typedef boost::function<IBaseClass*(std::unique_ptr<IBaseClass>&, std::unique_ptr<IBaseClass>&)> IBaseClassConstructorFunc_factory;
// Dummy base factory - no template
class UBaseClassTemplateFactory
{
public:
};
template<typename T>
class UClassFactoryTemplate : public UBaseClassTemplateFactory
{
private:
static std::map<string, IBaseClassConstructorFunc_factory> ClassFactoryTemplateMap; // Unique Classes only
public:
UClassFactoryTemplate();
__forceinline static UClassFactoryTemplate*Get()
{
static UClassFactoryTemplate<T> SingletonInstance;
return &SingletonInstance;
}
static std::unique_ptr<IBaseClass<T>> CreateClassTemplatized(string ClassString, std::unique_ptr<IBaseClass> LeftArgument, std::unique_ptr<IBaseClass> RightArgument);
};
// This type def we keep for non templatized base class
typedef boost::function<UBaseClassTemplateFactory*()> ClassFactoryTemplate_factory;
/* This is the instance class that resolves the classes as well as the concrete datatype to be used in UClassFactoryTemplate*/
class UClassFactory
{
private:
UClassFactory();
static std::map<EMyDataTypes, ClassFactoryTemplate_factory> ClassDataTypeTemplateFactoryMap;
public:
__forceinline static UClassFactory *Get()
{
static UClassFactory SingletonInstance;
return &SingletonInstance;
}
static std::unique_ptr<IBaseClass> CreateConcreteClass(string ClassString, std::unique_ptr<IBaseClass> LeftVal, std::unique_ptr<IBaseClass> RightVal, EMyDataTypes someEnumVal = EMyDataTypes::INT8);
};
Finally, in ClassFactory.cpp
#include "ClassFactory.h"
#include <boost/bind.hpp>
/*static, but non-const data members should be defined outside of the class definition
*and inside the namespace enclosing the class. The usual practice is to define it in
*the translation unit (*.cpp) because it is considered to be an implementation detail.
*Only static and const integral types can be declared and defined at the same time (inside class definition):*/
template<typename T>
std::map<string, IBaseClassConstructorFunc_factory> UClassFactoryTemplate<T>::ClassFactoryTemplateMap;
std::map<EMyDataTypes, ClassFactoryTemplate_factory> UClassFactory::ClassDataTypeTemplateFactoryMap;
template<typename T>
inline UClassFactoryTemplate<T>::UClassFactoryTemplate()
{
ClassFactoryTemplateMap[MyClassesNamespace::CLASS_A] = boost::bind(boost::factory<ConcreteClassA<T>*>(), _1, _2);
ClassFactoryTemplateMap[MyClassesNamespace::CLASS_B] = boost::bind(boost::factory<ConcreteClassB<T>*>(), _1, _2);
ClassFactoryTemplateMap[MyClassesNamespace::CLASS_C] = boost::bind(boost::factory<ConcreteClassC<T>*>(), _1, _2);
}
template<typename T>
std::unique_ptr<IBaseClass<T>> UClassFactoryTemplate<T>::CreateClassTemplatized(string ClassString, std::unique_ptr<IBaseClass> LeftArgument, std::unique_ptr<IBaseClass> RightArgument)
{
std::unique_ptr<IBaseClass<T>> someTemplatizedDataTypeInstance{ ClassFactoryTemplateMap.at(ClassString) (LeftArgument,RightArgument) };
return someTemplatizedDataTypeInstance;
}
UClassFactory::UClassFactory()
{
ClassDataTypeTemplateFactoryMap[EMyDataTypes::INT8] = boost::bind(boost::factory<UClassFactoryTemplate<int>*>());
ClassDataTypeTemplateFactoryMap[EMyDataTypes::FLOAT8] = boost::bind(boost::factory<UClassFactoryTemplate<float>*>());
ClassDataTypeTemplateFactoryMap[EMyDataTypes::FLOAT16] = boost::bind(boost::factory<UClassFactoryTemplate<double>*>());
}
std::unique_ptr<IBaseClass> UClassFactory::CreateConcreteClass(string ClassString, std::unique_ptr<IBaseClass> LeftVal, std::unique_ptr<IBaseClass> RightVal, EMyDataTypes someEnumVal)
{
std::unique_ptr<UBaseClassTemplateFactory> BaseOperatorTempFactory{ ClassDataTypeTemplateFactoryMap.at(someEnumVal) };
return BaseOperatorTempFactory->Get()::CreateClassTemplatized(ClassString, LeftVal, RightVal);
}
The question now is, the above code does not even compile let alone run, it says abstract class cannot be instantiated for the templatized map. I just want the UClassFactory to return me correct instantiated class like A,B,C based on a string map with correct datatypes based on an enum. How do I achieve this combination? I wonder what is the correct syntax? Or is my approach inherently flawed? Or there is a nice way to instantiate classes with factory pattern and different datatypes? Please let me know any suggestions/ comments.
Thanks
Alam