How to sort a std::set with const getters

Question

I have a std::set container whose elements are objects of the following class:

class LaneConnector {
public:

    const Lane* getLaneFrom() const {
        r         


        

Answer 1

First, you cannot sort an std::set. It is a sorted structure, sorting happens upon construction or insertion.

Second, you can construct an std::set with your own sorting functor, and you can avoid unnecessary const_casts by making it take const pointers:

struct MyLaneConectorSorter {
  bool operator() (const LaneConnector* lhs, const LaneConnector* rhs) const
  {
    // you may want to put some null pointer checks in here
    const Lane* a = lhs->getLaneFrom();
    const Lane* b = rhs->getLaneFrom();
    return a->getLaneID() < b->getLaneID();
  }
};

and instantiate the set like this:

std::set<LaneConnector*, MyLaneConectorSorter> s(MyLaneConectorSorter());

or, if you want to construct it from a different set, with a different ordering,

std::set<LaneConnector*> orig = ..... ;
....
std::set<LaneConnector*, MyLaneConectorSorter> s(orig.begin(), orig.end(), MyLaneConectorSorter());