Fast way to implement pop_front to a std::vector

Question

I\'m using some classes and several utility methods that use std:: vector.

Now I need to use each frame a pop_front - push_back method on one of those classes (but they

Answer 1

I would expect:

template
void pop_front(std::vector& vec)
{
    assert(!vec.empty());
    vec.front() = std::move(vec.back());
    vec.pop_back();
}

to be the most efficient way of doing this, but it does not maintain the order of the elements in the vector.

If you need to maintain the order of the remaining elements in vec, you can do:

template
void pop_front(std::vector& vec)
{
    assert(!vec.empty());
    vec.erase(vec.begin());
}

This will have linear time in the number of elements in vec, but it is the best you can do without changing your data structure.

Neither of these functions will maintain the vector at a constant size, because a pop_front operation will by definition remove an element from a container.