From 1f73f8028fffce5c737412b9e8fb1b5145f67a33 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Thu, 28 May 2020 14:51:11 -0400
Subject: util: Add a wrapper to implement Ord on top of PartialOrd

This allows nearest neighbors implementations to sort things by distance
or coordinate.
---
 src/lib.rs  |  2 ++
 src/util.rs | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 src/util.rs

diff --git a/src/lib.rs b/src/lib.rs
index 2f6504a..897a5e9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,8 @@ pub mod distance;
 pub mod euclid;
 pub mod exhaustive;
 
+mod util;
+
 pub use coords::Coordinates;
 pub use distance::{Distance, Metric, Proximity};
 pub use euclid::{euclidean_distance, Euclidean, EuclideanDistance};
diff --git a/src/util.rs b/src/util.rs
new file mode 100644
index 0000000..f838a9b
--- /dev/null
+++ b/src/util.rs
@@ -0,0 +1,54 @@
+//! Internal utilities.
+
+use std::cmp::Ordering;
+
+/// A wrapper that converts a partial ordering into a total one by panicking.
+#[derive(Clone, Copy, Debug, PartialEq, PartialOrd)]
+pub struct Ordered<T>(T);
+
+impl<T> Ordered<T> {
+    /// Wrap a value.
+    pub fn new(item: T) -> Self {
+        Self(item)
+    }
+}
+
+impl<T> From<T> for Ordered<T> {
+    fn from(item: T) -> Self {
+        Self::new(item)
+    }
+}
+
+impl<T: PartialOrd> Ord for Ordered<T> {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.partial_cmp(other).expect("Comparison between unordered items")
+    }
+}
+
+impl<T: PartialEq> Eq for Ordered<T> {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_ordered() {
+        let one = Ordered::new(1.0);
+        let two = Ordered::new(2.0);
+
+        assert_eq!(one.cmp(&one), Ordering::Equal);
+        assert_eq!(one.cmp(&two), Ordering::Less);
+        assert_eq!(two.cmp(&one), Ordering::Greater);
+    }
+
+    #[test]
+    #[should_panic(expected = "Comparison between unordered items")]
+    fn test_unordered() {
+        let one = Ordered::new(1.0);
+        let nan = Ordered::new(f64::NAN);
+
+        assert!(!(one < nan));
+        assert!(!(nan < one));
+        let _ = one.cmp(&nan);
+    }
+}
-- 
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