Take a careful look at this:
#include <iostream>
class Gadget
{
public:
void sayHello() const
{
std::cout << "Gadget!" << std::endl;
}
};
class Widget
{
public:
void sayHello() const
{
std::cout << "Widget!" << std::endl;
}
};
template <class T>
class OpNewCreator
{
public:
T* create()
{
std::cout << "Using 'new': ";
return new T;
}
};
template <class T>
class MallocCreator
{
public:
T* create()
{
std::cout << "Using 'malloc': ";
void* buf = std::malloc(sizeof(T));
if (!buf) return 0;
return new(buf) T;
}
};
template <class T, class B>
class Creator : public T<B>
{
public:
void exec()
{
B* obj = this->create();
obj->sayHello();
delete obj;
}
};
typedef Creator<MallocCreator, Widget> Manager;
int main (int argc, char * const argv[])
{
Manager obj;
obj.exec();
return 0;
}
Try changing MallocCreator by OpNewCreator and Widget by Gadget in the typedef of line 57, recompile and run; of course you can provide default values, so that
template <class T = MallocCreator, class B = Widget>
class Creator : public T<B>
so that you just do
typedef Creator<>; Manager;
I’ve just started reading “Modern C++ Design” by Andrei Alexandrescu and I’ve already my head spinning out of orbit. This is amazing (and by giving a quick look at the rest of the book, there’s even more incredible stuff there)!