Is there a difference between using .begin() vs .end() for std::inserter for std::set?

Question

If there is any difference between it1 and it2?

std::set s;

auto it1 = std::inserter(s, s.begin());
auto it2 = std::inserter(s, s.end());
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Answer 1

In practice, not much. If you're inserting a large number of already in order elements into an empty set, the second will be somewhat faster, but that's about it. std::insert_iterator calls insert with the iterator; std::set interprets it as a hint, and inserts in constant time (rather than lg n) if the insertion is immediately before the hint. (Actually, if the set is empty, I think both will do exactly the same thing.)