Something like boost::any

I was working out a way to implement some type of generic object, something similar to boost::any. I don't have any boost sources laying around, so I'm not quite sure how they achieve it.

This is what I came up with so far:

Code:

---

template <typename T>
inline const char* TypeOf()
{
        return typeid(T).name();
}

template <typename T>
inline const char* TypeOf(T obj)
{
        return typeid(obj).name();
}

class Object
{
        void* ptr;
        const char* m_type;

public:

        template <typename T>
        Object(T obj)
        {
                m_type = TypeOf(obj);
                ptr = new T(obj);
        }

        Object(Object& obj)
        {
                m_type = obj.m_type;
                ptr = obj.ptr;
                obj.ptr = 0;
        }

        ~Object()
        {
                if(ptr) delete ptr;
        }

        template <typename T>
        operator T()
        {
                return *((T*)ptr);
        }

        const char* Type() const
        {
                return m_type;
        }
};

---

Code:

---

int main()
{
        vector<Object> objects;
        objects.push_back(42);
        objects.push_back(88);
        objects.push_back(3.14159f);
        objects.push_back('c');
        objects.push_back(string("Hello!"));
        objects.push_back(1337L);

        auto lambda = [](Object obj)
        {
                if(obj.Type() == TypeOf<int>())
                {
                        cout << static_cast<int>(obj) << "\n";
                }
                else if(obj.Type() == TypeOf<float>())
                {
                        cout << static_cast<float>(obj) << "\n";
                }
                else if(obj.Type() == TypeOf<char>())
                {
                        cout << static_cast<char>(obj) << "\n";
                }
                else if(obj.Type() == TypeOf<string>())
                {
                        cout << static_cast<string>(obj) << "\n";
                }
                else
                {
                        cout << "Unknown type" << "\n";
                }
        };

        for_each(objects.begin(), objects.end(), lambda);
        system("PAUSE");
        return 0;
}

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Quote:

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Originally Posted by Chris_F

I was working out a way to implement some type of generic object, something similar to boost::any. I don't have any boost sources laying around, so I'm not quite sure how they achieve it.

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I don't think that type_info::name is guaranteed to return a unique name for each type.

Couple of points about your code:

Quote:

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Originally Posted by Chris_F

Code:

---

        Object(Object& obj)
        {
                m_type = obj.m_type;
                ptr = obj.ptr;
                obj.ptr = 0;
        }

---

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That's not a good idea. This gives you the same behavior as std::auto_ptr, which will be deprecated in C++0x for good reason. You won't be able to safely store your objects in a vector (which seems somewhat the point of having a class like boost::any).
Since you are using other C++0x features, why not make the object movable?

Quote:

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Originally Posted by Chris_F

Code:

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        ~Object()
        {
                if(ptr) delete ptr;
        }

---

---

Deleting a void* is undefined behavior.

First, boost::any does not use a void* in its implementation of the type. Second, you would need to have type_info to store type information on the encapsulated object but you shouldn't use the name for the reason as suggested by D_Drmmr.

Have a look at this blogpost for some background on boost::any: here and then you can also refer to the boost code by following the link provided there. If you do have boost on your system, you should be able to access their code.