How to get the index of a value in a vector using for_each?

In C++14 thanks to generalized lambda captures you can do something like so:

std::vector<int> v(10);
std::for_each(v.begin(), v.end(), [idx = 0] (int i) mutable {
    // your code...
    ++idx; // 0, 1, 2... 9
});