lambda

using Algo = std::function<void (int)> ;


double lengthMeters = 5;

Length<Meters> a = 5;
Length<Nm> b = 5;

auto square = a * b;


int sum = 0;
auto algo = [sum](int element){sum += element;};
Algo algo22 = [sum](int element){sum += element/2;};

void treeWidth(Algo algo);
{
    ...
    el = ...
    algo(el);
    ...

    print(sum)
}

void treeDepth(Algo algo)
{
    ...
    el = ...
    algo(el);
    ...

    print(sum)
}

void run()
{
    treeDepth(algo);
    treeWidth(algo22);
}