Question

Comming from Java I would like to implement the following “test multiple implementations” idiom in C++

void testMethod() {
    List veryBigList = createNewRandomList(10000);
    Algo algo = createAlgo(veryBigList);
    algo.run();
}

// this can be overwritten from a subclass to test against different algo
Algo createAlgo(List list) {
    Algo a(list);
    return a;
}

List createNewRandomList(int size) {
    List l = new ArrayList(size);
    // fill list with random objects
    return l;
}

I’m a bit lost how to do this the right way in C++ … when I’m doing it this way:

void test_method() {
    vector<string> big_list(10000);
    init_random_list(big_list);
    algo my_algo = create_algo(big_list);
    my_algo.run();
}

algo create_algo(vector<string> list) {
    algo a(list);
    return a;
}

void init_random_list(vector<string> list) {
    // fill list with random objects        
}

then what will C++ do? Will it copy the full list to go to create_algo and then on return it’ll copy the algo (and the list again)??

But when using call by reference I would access the reference in test_method outside of the scope of algo causing a lot trouble and violating the RAII principle, right?

I know for some implementations of C++ they optimize speed for call by value according to this doc, but can I rely on that for g++ and visual c++?

Answer 1

Assuming that the code is exactly as you posted, and that algo can be modified to store a reference, then you probably want to pass and store a reference.