c++11 Template Factory pattern and constructor with parameters - c++

Question

I'm trying to make a c++11 templated factory with automatic registration,
I pretty much followed this: http://www.drdobbs.com/conversations-abstract-factory-template/184403786
So I have a AFactory like this:
template<class BaseType, typename IDKey = std::string>
class AFactory : public Singleton<AFactory<BaseType, IDKey>>
{
friend class Singleton<AFactory>;
private:
typedef std::unique_ptr<BaseType>(*typeCreator)();
public:
AFactory() = default;
~AFactory() = default;
AFactory(const AFactory&) = delete;
AFactory& operator=(const AFactory&) = delete;
void registerNewClass(const IDKey& key, const typeCreator& creator)
{
_registerTypes.insert({key, creator});
};
template<typename... Args>
std::unique_ptr<BaseType> create(const IDKey& key, Args&&... args) const
{
return (_registerTypes.at(key))(std::forward<Args>(args)...);
};
private:
std::unordered_map<IDKey, typeCreator> _registerTypes;
};
And a registration class like that:
template<class BaseType, class RealType, typename IDKey = std::string>
class AFactoryRegistration
{
public:
AFactoryRegistration(const IDKey& key)
{
AFactory<BaseType>::instance().registerNewClass(key, &instancier);
};
~AFactoryRegistration() = default;
AFactoryRegistration(const AFactoryRegistration&) = delete;
AFactoryRegistration& operator=(const AFactoryRegistration&) = delete;
static std::unique_ptr<BaseType> instancier()
{
return std::unique_ptr<BaseType>(new RealType());
};
};
But I still have a problem with classes which take construction parameters.
For example if I have a class:
class Point : public stuff
{
public:
Point(int x, int y);
/*...*/
};
How can I register the class Point to the factory taking the constructor Point(int x, int y) ?

Answer 1

Wow. A four year old question. Maybe std::any would help. You can store anything in std::any.
The any_cast is a little bit tricky.
See below example:
#include <iostream>
#include <map>
#include <utility>
#include <any>
// Some demo classes ----------------------------------------------------------------------------------
struct Base {
Base(int d) : data(d) {};
virtual ~Base() { std::cout << "Destructor Base\n"; }
virtual void print() { std::cout << "Print Base\n"; }
int data{};
};
struct Child1 : public Base {
Child1(int d, std::string s) : Base(d) { std::cout << "Constructor Child1 " << d << " " << s << "\n"; }
virtual ~Child1() { std::cout << "Destructor Child1\n"; }
virtual void print() { std::cout << "Print Child1: " << data << "\n"; }
};
struct Child2 : public Base {
Child2(int d, char c, long l) : Base(d) { std::cout << "Constructor Child2 " << d << " " << c << " " << l << "\n"; }
virtual ~Child2() { std::cout << "Destructor Child2\n"; }
virtual void print() { std::cout << "Print Child2: " << data << "\n"; }
};
struct Child3 : public Base {
Child3(int d, long l, char c, std::string s) : Base(d) { std::cout << "Constructor Child3 " << d << " " << l << " " << c << " " << s << "\n"; }
virtual ~Child3() { std::cout << "Destructor Child3\n"; }
virtual void print() { std::cout << "Print Child3: " << data << "\n"; }
};
using UPTRB = std::unique_ptr<Base>;
template <class Child, typename ...Args>
UPTRB createClass(Args...args) { return std::make_unique<Child>(args...); }
// The Factory ----------------------------------------------------------------------------------------
template <class Key, class Object>
class Factory
{
std::map<Key, std::any> selector;
public:
Factory() : selector() {}
Factory(std::initializer_list<std::pair<const Key, std::any>> il) : selector(il) {}
template<typename Function>
void add(Key key, Function&& someFunction) { selector[key] = std::any(someFunction); };
template <typename ... Args>
Object create(Key key, Args ... args) {
if (selector.find(key) != selector.end()) {
return std::any_cast<std::add_pointer_t<Object(Args ...)>>(selector[key])(args...);
}
else return nullptr;
}
};
int main()
{
Factory<int, UPTRB> factory{
{1, createClass<Child1, int, std::string>},
{2, createClass<Child2, int, char, long>}
};
factory.add(3, createClass<Child3, int, long, char, std::string>);
// Some test values
std::string s1(" Hello1 "); std::string s3(" Hello3 ");
int i = 1; const int ci = 1; int& ri = i; const int& cri = i; int&& rri = 1;
UPTRB b1 = factory.create(1, 1, s1);
UPTRB b2 = factory.create(2, 2, '2', 2L);
UPTRB b3 = factory.create(3, 3, 3L, '3', s3);
b1->print();
b2->print();
b3->print();
b1 = factory.create(2, 4, '4', 4L);
b1->print();
return 0;
}
You could generalize it even more. But then is just a wrapper around a creator function.