Question

I have a class Bar which stores objects derived from BarItem:

#include <list>
#include <memory>

class Bar {
public:
    typedef std::shared_ptr<BarItem> item_ptr;

    void add_item(item_ptr item) {
        items_.push_back(item);
    }

private:
    std::list<item_ptr> items_;
};

I have another class Note which is a subclass of BarItem. Currently to add a copy of a Note object I am doing:

Bar my_bar;
Note my_note;

my_bar.add_item(Bar::item_ptr(new Note(my_note)));

Which is a bit ugly; I would like to know if there is a better way or a way to automate this?

Answer 1

You can’t actually avoid the copy (in C++11 you can make it a move), but you can “automate” it so you save a few keystrokes by overloading the add_item function for each type (that may be child of BarItem).

template <class T>
typedef enable_if<is_base_of<BarItem, T>::value,void>::type add_item(const T& item) { /* or T&& */
    items_.push_back(item_ptr(new T(item)));
}