Creating a new object from dynamic type info

Question

In C++, is there any way to query the type of an object and then use that information to dynamically create a new object of the same type?

For example, say I have a

Answer 1

I used macros in my project to synthesize such methods. I'm just researching this approach now, so I may be wrong, but here's an answer to your question in my code of IAllocable.hh. Note that I use GCC 4.8, but I hope 4.7 suits.

#define SYNTHESIZE_I_ALLOCABLE \
    public: \
    auto alloc() -> __typeof__(this) { return new (__typeof__(*this))(); } \
    IAllocable * __IAllocable_alloc() { return new (__typeof__(*this))(); } \
    private:


class IAllocable {
public:
    IAllocable * alloc() {
        return __IAllocable_alloc();
    }
protected:
    virtual IAllocable * __IAllocable_alloc() = 0;
};

Usage:

class Usage : public virtual IAllocable {

    SYNTHESIZE_I_ALLOCABLE

public:
    void print() {
        printf("Hello, world!\n");
    }
};

int main() {
    {
        Usage *a = new Usage;
        Usage *b = a->alloc();

        b->print();

        delete a;
        delete b;
    }

    {
        IAllocable *a = new Usage;
        Usage *b = dynamic_cast(a->alloc());

        b->print();

        delete a;
        delete b;
    }
 }

Hope it helps.