#include <iostream>
#include <vector>

template <typename iter>
void func(iter it)
{
    *it = (*it) * 2;
}

template <typename iter, typename func>
void myapply(iter begin, iter end, func f)
{
    for (iter it = begin; it != end; ++it) {
        f(it);
    }
}


int main()
{
    std::vector<int> v = {1, 2, 3, 4};
    myapply(v.begin(), v.end(), func);

    for (int c : v) {
        std::cout << c << std::endl;
    }

}