What's your preferred way of returning a list of items?

Hi,

Here are a couple of ways to return some list of items.

struct A
{
};

std::vector<A> aList; // Some list of items.

// Returning a copy.
std::vector<A> getList() { return aList; }

void getList( std::vector<A>& v )
{
    std::copy( aList.begin(), aList.end(), v.begin() );
}

void getList( std::vector<A>* v )
{
    std::copy( aList.begin(), aList.end(), v->begin() );
}

// Returning a reference to aList.
const std::vector<A>& getList() { return aList; }

const std::vector<A>::const_iterator& getList()
{
    return aList.begin();
}

Do you know more ways to return a list? What's your preferred way to
return a list of items?

Also, here comes another trickier one. Let's say I have a map instead
and want to return the keys.

std::map<std::string, A> aMap;

// Returning a copy of the keys.
std::vector<std::string> getList()
{
    std::vector<std::string> aKeys;
    auto keysEnd = aMap.end();
    for( auto i = aMap.begin(); i != keysEnd; ++i )
       aKeys.push_back( (*i).first );
    return aKeys;
}

void getList( std::vector<std::string>& v )
{
    auto keysEnd = aMap.end();
    for( auto i = aMap.begin(); i != keysEnd; ++i )
       v.push_back( (*i).first );
}

void getList( std::vector<std::string>* v )
{
    auto keysEnd = aMap.end();
    for( auto i = aMap.begin(); i != keysEnd; ++i )
       v->push_back( (*i).first );
}

// But is it even possible to return a reference to
// the keys in a map?

const std::vector<std::string>& getList() { /* What here? */ }

const std::vector<std::string>::const_iterator& getList()
{
    /* What here? */
}

How do you usually deal with these kind of list returns?

Thanks,
Daniel