Michael Fawcett wrote:
On 3/27/07, Noah Roberts <roberts.noah@gmail.com> wrote:
Nope. Your dialog manager would keep track of the unit and set appropriately upon initialization and/or user interaction. Your reader would then be as simple as setting the value directly to the quantity. Alternatively you might have something like this:
quantity<abstract> on_dialog_ok() { quantity<abstract> dist; dist.set_unit(combo.selected_item().data()); dist.set_value(entry.value().as_double()); }
I see. Would the implementation allocate a derived class based on the unit type, or just dispatch during arithmetic based on unit type? I suppose it works out to about the same penalty either way, virtual function or if statement for every arithmetic. It would probably be a lot cleaner to go the derived class route though.
No virtual function would be required. template < typename D > struct unit { double convert(double base_value) const { return base_value * cv_fact; } private: double cv_fact; }; D is the dimension and simply makes sure you don't intermix dimensions as it would be unassignable to any quantity except ones in the same dimension.