Generic way to cast int to enum in C++

Question

Is there a generic way to cast int to enum in C++?

If int falls in range of an enum it should return

Answer 1

What do you think about this one?

#include 
#include 
#include 
#include 

using namespace std;

template
class Enum
{
public:
    static void insert(int value)
    {
        _set.insert(value);
    }

    static T buildFrom(int value)
    {
        if (_set.find(value) != _set.end()) {
            T retval;
            retval.assign(value);
            return retval;
        }
        throw std::runtime_error("unexpected value");
    }

    operator int() const { return _value; }

private:
    void assign(int value)
    {
        _value = value;
    }

    int _value;
    static std::set _set;
};

template std::set Enum::_set;

class Apples: public Enum {};

class Oranges: public Enum {};

class Proxy
{
public:
    Proxy(int value): _value(value) {}

    template
    operator T()
    {
        T theEnum;
        return theEnum.buildFrom(_value);
    }

    int _value;
};

Proxy convert(int value)
{
    return Proxy(value);
}

int main()
{    
    Apples::insert(4);
    Apples::insert(8);

    Apples a = convert(4); // works
    std::cout << a << std::endl; // prints 4

    try {
        Apples b = convert(9); // throws    
    }
    catch (std::exception const& e) {
        std::cout << e.what() << std::endl; // prints "unexpected value"
    }
    try {
        Oranges b = convert(4); // also throws  
    }
    catch (std::exception const& e) {
        std::cout << e.what() << std::endl; // prints "unexpected value"
    }
}

You could then use code I posted here to switch on values.