Question

Which is the best way to implement several order relations for only one class? I have an idea with the Strategy Pattern but I’m not sure that’s a good idea. And if there is not a best way, why?

Answer 1

Create a functor class and initialize a member with the order relation you want to use. Have operator() use the member to decide the ordering of the two operands.

class Ordering
{
public:
    Ordering(int method) : _method(method) {}
    bool operator()(const MyObject & first, const MoObject & second) const
    {
        switch(_method)
        {
            case 0:
                return first.name < second.name;
            case 1:
                return first.age < second.age;
            // ...
        }
    }
    int _method;  // an enum would be better
};

std::sort(myobjs.begin(), myobjs.end(), Ordering(selected_method));