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use std::cmp::Ordering;
use Ordering::*;
#[inline]
pub const fn bool_cmp(left: bool, right: bool) -> Ordering {
match (left, right) {
(true, false) => Greater,
(false, true) => Less,
_ => Equal,
}
}
#[inline]
pub const fn lattice_ord(left: Ordering, right: Ordering) -> Option<Ordering> {
match (left, right) {
(Equal, right) => Some(right),
(left, Equal) => Some(left),
(Greater, Greater) => Some(Greater),
(Less, Less) => Some(Less),
(Greater, Less) | (Less, Greater) => None,
}
}
#[inline]
pub const fn lattice_ord_opt(left: Option<Ordering>, right: Option<Ordering>) -> Option<Ordering> {
match (left, right) {
(Some(left), Some(right)) => lattice_ord(left, right),
_ => None,
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn bool_cmp_test() {
let bools = [true, false];
for &l in &bools {
for &r in &bools {
assert_eq!(bool_cmp(l, r), l.cmp(&r))
}
}
}
#[test]
fn lattice_ord_test() {
let tuples = [
(Less, Less, Some(Less)),
(Less, Equal, Some(Less)),
(Less, Greater, None),
(Equal, Equal, Some(Equal)),
(Equal, Greater, Some(Greater)),
(Greater, Greater, Some(Greater)),
];
for &(left, right, result) in tuples.iter() {
assert_eq!(lattice_ord(left, right), result);
assert_eq!(lattice_ord_opt(Some(left), Some(right)), result);
}
for &ord in &[Less, Equal, Greater] {
assert_eq!(lattice_ord_opt(Some(ord), None), None);
assert_eq!(lattice_ord_opt(None, Some(ord)), None);
}
}
}