extent

This is an alternative to std::ops::{Range,RangeInclusive}, avoiding the quirks of those types (non-Copy, inability to produce empty inclusive ranges without extra bool, directly implementing Iterator, etc). See https://ridiculousfish.com/blog/posts/least-favorite-rust-type.html and https://kaylynn.gay/blog/post/rust_ranges_and_suffering for its litany of sins.

I was coincidentally writing this type in one of my own crates today when I saw the second post go by, so I figured I'd split it out and post it as a crate others can use. It has some quirks and limitations of its own but it suits my needs better than the builtins. Here are the choices I made:

1. Extent represents an inclusive range of numbers, where number is N:PrimInt from the (fairly standard) num-traits crate. It is inclusive because (at least the most obvious representations of) exclusive ranges can't represent the maximum number of a number-type, which in my experience one fairly often needs to represent!

2. Extent uses exactly 2 numbers and no extra flags or wasted space.

3. Extent can represent empty ranges. Empty ranges are represented with a normalized form of {lo=1, hi=0}. This is the only case for which lo > hi and is only constructable via the static function empty or the IO-oriented function new_unchecked. Typical accessors for endpoints lo() and hi() return an Option<N> with None in the empty case. If you want the raw form (eg. for doing IO) you can call lo_unchecked() or hi_unchecked(), which are marked unsafe as they do not reflect the significant lo <= hi invariant.

4. All nonempty cases have lo <= hi enforced in new. If you pass hi > lo to new, the values are swapped (i.e. you can construct from either order of points; they get stored in order). If you are constructing from raw IO values you can do new_unchecked which will not swap, only normalize unordered ranges to empty(), and is also unsafe.

5. Extent implements Copy (and everything else standard).

6. Extent does not implement Iterator, but it has an iter method that copies Extent into ExtentIter, which does implement Iterator.

7. There is also an ExtentRevIter that counts down.

8. Some basic set-like operators are provided (union, intersection, contains) but nothing too fancy.

Patches are welcome to enrich this further, though I will try to keep it fairly simple and focused on the use-case of number-ranges, not "arbitrary thing ranges".

License: MIT OR Apache-2.0