The changes from the One Ranges Proposal amount to adding:
- a constructor that takes a `default_sentinel_t` and is equivalent to
the default constructor;
- an `operator==` that compares the iterator to `default_sentinel_t`.
The original proposal defined two overloads for `operator==` (different
argument order) as well as `operator!=`. This has been removed by
[P1614](https://wg21.link/p1614).
Differential Revision: https://reviews.llvm.org/D119620
This must have been meant to be friend-declaring operator!=, but it
turns out that it's not even necessary to make it a friend since it
does not access any private state.
rdar://82568613
Konstantin Varlamov