How come std::distance() doesn't work for rvalues?

Question

For example:

std::list <int> list1 = {1, 2, 3, 4, 5};
auto first = list1.begin();

std::cout <<  std::distance(--first, ++first);

The output is 0. Strange enough, if we change --first to first--, the output becomes 5 (although here it should be 0, as it returns first). What am I missing?

Answer 1

Neither --first nor ++first is an rvalue. They are lvalues.

You are also not allowed to decrement the iterator returned by begin().

To get the distance between two rvalues, you could use std::prev and std::next:

auto second = std::next(list1.begin()); // to make std::prev(second) ok

std::cout <<  std::distance(std::prev(second), std::next(second));