discrete_range_map/README.md

range_bounds_map

This crate provides RangeBoundsMap and RangeBoundsSet.

RangeBoundsMap is an ordered map of non-overlapping RangeBounds based on BTreeMap.

RangeBoundsSet is an ordered set of non-overlapping RangeBounds based on RangeBoundsMap.

Example using Ranges

use range_bounds_map::RangeBoundsMap;

let mut map = RangeBoundsMap::new();

map.insert_strict(0..5, true);
map.insert_strict(5..10, false);

assert_eq!(map.overlaps(&(-2..12)), true);
assert_eq!(map.contains_point(&20), false);
assert_eq!(map.contains_point(&5), true);

Example using a custom RangeBounds type

use std::ops::{Bound, RangeBounds};

use range_bounds_map::RangeBoundsMap;

#[derive(Debug)]
enum Reservation {
	// Start, End (Inclusive-Inclusive)
	Finite(u8, u8),
	// Start (Exclusive)
	Infinite(u8),
}

// First, we need to implement RangeBounds
impl RangeBounds<u8> for Reservation {
	fn start_bound(&self) -> Bound<&u8> {
		match self {
			Reservation::Finite(start, _) => {
				Bound::Included(start)
			}
			Reservation::Infinite(start) => {
				Bound::Excluded(start)
			}
		}
	}
	fn end_bound(&self) -> Bound<&u8> {
		match self {
			Reservation::Finite(_, end) => Bound::Included(end),
			Reservation::Infinite(_) => Bound::Unbounded,
		}
	}
}

// Next we can create a custom typed RangeBoundsMap
let reservation_map = RangeBoundsMap::try_from([
	(Reservation::Finite(10, 20), "Ferris".to_string()),
	(Reservation::Infinite(20), "Corro".to_string()),
])
.unwrap();

for (reservation, name) in reservation_map.overlapping(&(16..17))
{
	println!(
		"{name} has reserved {reservation:?} inside the range 16..17"
	);
}

for (reservation, name) in reservation_map.iter() {
	println!("{name} has reserved {reservation:?}");
}

assert_eq!(
	reservation_map.overlaps(&Reservation::Infinite(0)),
	true
);

Key Definitions:

Invalid RangeBounds

Within this crate, not all RangeBounds are considered valid RangeBounds. The definition of the validity of a RangeBounds used within this crate is that a RangeBounds is only valid if it contains at least one value of the underlying domain.

For example, 4..6 is considered valid as it contains the values 4 and 5, however, 4..4 is considered invalid as it contains no values. Another example of invalid RangeBounds are those with start_bound()s with greater values than their end_bound()s, such as 5..2 or 100..=40.

Here are a few examples of RangeBounds and whether they are valid:

RangeBounds	Valid
0..0	NO
0..1	YES
9..8	NO
(0.4)..=(-0.2)	NO
..(-3)	YES
0.0003..	YES
..	YES
400..=400	YES

Overlap

Two RangeBounds are "overlapping" if there exists a point that is contained within both RangeBounds.

Touching

Two RangeBounds are "touching" if they do not overlap and there exists no value between them. For example, 2..4 and 4..6 are touching but 2..4 and 6..8 are not, neither are 2..6 and 4..8.

Merging

When a RangeBounds "merges" other RangeBounds it absorbs them to become larger.

Further Reading

See Wikipedia's article on Intervals: https://en.wikipedia.org/wiki/Interval_(mathematics)

Improvements/Caveats

• Missing some functions common to BTreeMap and BTreeSet like:
  • clear()
  • is_subset()
  • etc... prob a bunch more
• Not particularly optimized, (which doesn't mean it's neccessarily slow)
• Can't use TryFrom<(Bound, Bound)> instead of [TryFromBounds] (relys on upstream to impl, see this thread)

Credit

I originally came up with the StartBound: Ord bodge on my own, however, I later stumbled across rangemap which also used a StartBound: Ord bodge. rangemap then became my main source of inspiration.

The aim for my library was to become a more generic superset of rangemap, following from this issue and this pull request in which I changed rangemap's RangeMap to use RangeBoundss as keys before I realized it might be easier and simpler to just write it all from scratch. Which ended up working really well with some simplifications (BoundOrd) I made which made some of the code much easier to work with.

Similar Crates

Here are some relevant crates I found whilst searching around the topic area:

• https://docs.rs/rangemap Very similar to this crate but can only use Ranges and RangeInclusives as keys in it's map and set structs (separately).
• https://docs.rs/btree-range-map
• https://docs.rs/ranges Cool library for fully-generic ranges (unlike std::ops ranges), along with a Ranges datastructure for storing them (Vec-based unfortunately)
• https://docs.rs/intervaltree Allows overlapping intervals but is immutable unfortunately
• https://docs.rs/nonoverlapping_interval_tree Very similar to rangemap except without a gaps() function and only for Ranges and not RangeInclusives. And also no fancy coalescing functions.
• https://docs.rs/unbounded-interval-tree A data structure based off of a 2007 published paper! It supports any RangeBounds as keys too, except it is implemented with a non-balancing Box<Node> based tree, however it also supports overlapping RangeBounds which my library does not.
• https://docs.rs/rangetree I'm not entirely sure what this library is or isn't, but it looks like a custom red-black tree/BTree implementation used specifically for a Range Tree. Interesting but also quite old (5 years) and uses unsafe.