range_bound_cmp

Range Bound Cmp

Comparison operations between primitive Bound values.

Usage

range_bound_cmp aims to simplify set operations on primitive ranges by providing lower and upper bound specific implementations of PartialEq, Eq, PartialOrd and Ord. This allows for comparison of values rather than variants. Take for example the following assertions:

assert!(Bound::Included(9) != Bound::Excluded(10));

// The above is `false` for `LowerBound` but `true` for `UpperBound`.
assert!(LowerBound(Bound::Included(9)) != LowerBound(Bound::Excluded(10)));
assert!(UpperBound(Bound::Included(9)) == UpperBound(Bound::Excluded(10)));

// Therefore we can make more assertions for the entire range.
assert!(OrdRange::new(0..9) != OrdRange::new(0..10));
assert!(OrdRange::new(0..=9) == OrdRange::new(0..10));

Passing a range into OrdRange will wrap the bounds for comparison operations. Use the RangeBound implementation on OrdRange, or call take to return the unwrapped bounds for operations such as slicing into an array. Range bound assertions are particularly useful in the development of range set algorithms. Take for example this naive implementation of intersection below:

// Our return type.
pub type TupleRange<T> = (Bound<T>, Bound<T>);

/// Get the range of elements in both sets `a` and `b`.
fn intersection(a: impl RangeBounds<usize>, b: impl RangeBounds<usize>) -> OrdRange<usize> {
    let a = OrdRange::new(a);
    let b = OrdRange::new(b);

    // Conversion is infallible for this operation.
    OrdRange::try_from((a.start.max(b.start), a.end.min(b.end))).unwrap()
}

assert_eq!(intersection((0..7), (3..10)).take(), (Bound::Included(3), Bound::Excluded(7)));

Lower and Upper bound conversion

Conversion between LowerBound and UpperBound using TryFrom or TryInto has the following behaviour:

• Bound variant is always maintained. LowerBound::Included(5) will be converted to UpperBound::Included(5) while LowerBound::Excluded(4) will be converted to UpperBound::Excluded(6).
• Bound::Unbounded conversion is always an error. The lower bound of ..10 is not equal to the upper bound of 0...

License: MIT OR Apache-2.0