From 82df66b852fd2e16f3ab5cc0b4bbf32034ee49db Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Thu, 28 May 2020 14:41:22 -0400
Subject: coords: Implement coordinate spaces

---
 src/coords.rs | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs    |   2 ++
 2 files changed, 115 insertions(+)
 create mode 100644 src/coords.rs

(limited to 'src')

diff --git a/src/coords.rs b/src/coords.rs
new file mode 100644
index 0000000..c43b7e9
--- /dev/null
+++ b/src/coords.rs
@@ -0,0 +1,113 @@
+//! Coordinate spaces.
+
+use crate::distance::{Distance, Value};
+
+/// A coordinate space.
+pub trait Coordinates {
+    /// The type of individual coordinates.
+    type Value: Value;
+
+    /// Get the number of dims this point has.
+    fn dims(&self) -> usize;
+
+    /// Get the `i`th coordinate of this point.
+    fn coord(&self, i: usize) -> Self::Value;
+
+    /// Create a vector with this point's coordinates as values.
+    fn as_vec(&self) -> Vec<Self::Value> {
+        let len = self.dims();
+        let mut vec = Vec::with_capacity(len);
+        for i in 0..len {
+            vec.push(self.coord(i));
+        }
+        vec
+    }
+}
+
+/// [Coordinates] implementation for slices.
+impl<T: Value> Coordinates for [T] {
+    type Value = T;
+
+    fn dims(&self) -> usize {
+        self.len()
+    }
+
+    fn coord(&self, i: usize) -> T {
+        self[i]
+    }
+}
+
+/// [Coordinates] implementation for arrays.
+macro_rules! array_coordinates {
+    ($n:expr) => (
+        impl<T: Value> Coordinates for [T; $n] {
+            type Value = T;
+
+            fn dims(&self) -> usize {
+                $n
+            }
+
+            fn coord(&self, i: usize) -> T {
+                self[i]
+            }
+        }
+    );
+}
+
+array_coordinates!(1);
+array_coordinates!(2);
+array_coordinates!(3);
+array_coordinates!(4);
+array_coordinates!(5);
+array_coordinates!(6);
+array_coordinates!(7);
+array_coordinates!(8);
+
+/// [Coordinates] implemention for vectors.
+impl<T: Value> Coordinates for Vec<T> {
+    type Value = T;
+
+    fn dims(&self) -> usize {
+        self.len()
+    }
+
+    fn coord(&self, i: usize) -> T {
+        self[i]
+    }
+}
+
+/// Blanket [Coordinates] implementation for references.
+impl<T: ?Sized + Coordinates> Coordinates for &T {
+    type Value = T::Value;
+
+    fn dims(&self) -> usize {
+        (*self).dims()
+    }
+
+    fn coord(&self, i: usize) -> Self::Value {
+        (*self).coord(i)
+    }
+}
+
+/// Types that support computing distances to raw slices of coordinates.
+pub trait CoordinateProximity<T> {
+    type Distance: Distance;
+
+    /// Compute the distance to a point specified by its coordinates.
+    fn distance_to_coords(&self, coords: &[T]) -> Self::Distance;
+}
+
+/// Blanket [CoordinateProximity] implementation for references.
+impl<T: CoordinateProximity<U>, U> CoordinateProximity<U> for &T {
+    type Distance = T::Distance;
+
+    fn distance_to_coords(&self, coords: &[U]) -> Self::Distance {
+        (*self).distance_to_coords(coords)
+    }
+}
+
+/// Marker trait for coordinate proximities that are [metrics][crate::distance::Metric].
+pub trait CoordinateMetric<T>: CoordinateProximity<T> {}
+
+/// Blanket [CoordinateMetric] implementation for references.
+impl<T: CoordinateMetric<U>, U> CoordinateMetric<U> for &T {}
diff --git a/src/lib.rs b/src/lib.rs
index 8b0c32b..1532211 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,6 +2,8 @@
 //!
 //! [nearest neighbor search]: https://en.wikipedia.org/wiki/Nearest_neighbor_search
 
+pub mod coords;
 pub mod distance;
 
+pub use coords::Coordinates;
 pub use distance::{Distance, Metric, Proximity};
-- 
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