C++17 STL Cookbook

How it works...

The quick_remove_at function removes items pretty quickly without touching too many other items. It does this in a relatively creative way: It kind of swaps the actual item,  which shall be removed with the last item in the vector. Although the last item has no connection to the actually selected item, it is in a special position: Removing the last item is cheap! The vector's size just needs to be shrunk down by one slot, and that's it. No items are moved during that step. Have a look at the following diagram which helps imaging how this happens:

Both the steps in the recipe code look like this:

 v.at(idx) = std::move(v.back()); ...