Clean ways to write multiple 'for' loops

Question

For an array with multiple dimensions, we usually need to write a for loop for each of its dimensions. For example:

vector< vector< vector         


        

Answer 1

One technique I've used is templates. E.g.:

template void do_something_on_A(std::vector &vec) {
    for (auto& i : vec) { // can use a simple for loop in C++03
        do_something_on_A(i);
    }
}

void do_something_on_A(int &val) {
    // this is where your `do_something_on_A` method goes
}

Then you simply call do_something_on_A(A) in your main code. The template function gets created once for each dimension, the first time with T = std::vector>, the second time with with T = std::vector.

You could make this more generic using std::function (or function-like objects in C++03) as a second argument if you want:

template void do_something_on_vec(std::vector &vec, std::function &func) {
    for (auto& i : vec) { // can use a simple for loop in C++03
        do_something_on_vec(i, func);
    }
}

template void do_something_on_vec(T &val, std::function &func) {
    func(val);
}

Then call it like:

do_something_on_vec(A, std::function(do_something_on_A));

This works even though the functions have the same signature because the first function is a better match for anything with std::vector in the type.