Create std::list with std::multimap iterators

Question

I have the following function:

std::list<std::shared_ptr<Object>> AnimalManager::GetObjectsOfType(std::string type)
{    
    std::pair <std::multimap<std::string, std::shared_ptr<Object>>::iterator, std::multimap<std::string, std::shared_ptr<Object>>::iterator> ret;
    ret = m_objects.equal_range(type);

    std::list<std::shared_ptr<Object>> objectsOfType(ret.first, ret.second);

    return objectsOfType;
}

I'm creating a list with a range of iterators but I'm getting an error. I due to the iterators in the multimap are pairs and elements in list are uniques. But I don't want to iterate thought iterators because I'll lose the benefit I get using std::multimap instead other data strcuture with O(1) insertion but O(n) find.

Is possible to create a list as I want to do it? Or would it be better If I use another design pattern or data structure?

Answer 1

What you need it std::transform to transform the range into a different one. Making use of a lambda you could construct the list like

std::list<std::shared_ptr<Object>> AnimalManager::GetObjectsOfType(std::string type)
{    
    auto ret = m_objects.equal_range(type);

    std::list<std::shared_ptr<Object>> objectsOfType;
    std::transform((ret.first, ret.second, std::back_inserter(objectsOfType),
                   [](const auto& pair){ return pair.second; });

    return objectsOfType;
}