Implement broadcasting trait for matrices and enhance element-wise comparison methods

src/matrix/mat.rs

@@ -183,24 +183,52 @@ impl<'a, T> MatrixRow<'a, T> {
         (0..self.matrix.cols).map(move |c| &self.matrix[(self.row, c)])
     }
 }
+/// A trait to turn either a Matrix<T> or a scalar T into a Vec<T> of 
+/// length rows*cols (broadcasting the scalar).
+pub trait Broadcastable<T> {
+    fn to_vec(&self, rows: usize, cols: usize) -> Vec<T>;
+}
 
-/// Implements element‐wise eq, lt, le, gt and ge for `Matrix<T>`.
+impl<T: Clone> Broadcastable<T> for T {
+    fn to_vec(&self, rows: usize, cols: usize) -> Vec<T> {
+        vec![self.clone(); rows * cols]
+    }
+}
+
+impl<T: Clone> Broadcastable<T> for Matrix<T> {
+    fn to_vec(&self, rows: usize, cols: usize) -> Vec<T> {
+        assert_eq!(self.rows, rows, "row count mismatch");
+        assert_eq!(self.cols, cols, "col count mismatch");
+        self.data.clone()
+    }
+}
+
+/// Generates element-wise eq, lt, le, gt and ge methods
+/// where the rhs can be a Matrix<T> or a scalar T.
 macro_rules! impl_elementwise_cmp {
     (
         $( $method:ident => $op:tt ),* $(,)?
     ) => {
-        impl<T: PartialOrd> Matrix<T> {
+        impl<T: PartialOrd + Clone> Matrix<T> {
             $(
-            #[doc = concat!("Element‐wise comparison `x ", stringify!($op), " y`.")]
-            pub fn $method(&self, rhs: &Matrix<T>) -> BoolMatrix {
-                assert_eq!(self.rows, rhs.rows, "row count mismatch");
-                assert_eq!(self.cols, rhs.cols, "col count mismatch");
+            #[doc = concat!("Element-wise comparison `self ", stringify!($op), " rhs`,\n\
+                             where `rhs` may be a Matrix<T> or a scalar T.")]
+            pub fn $method<Rhs>(&self, rhs: Rhs) -> BoolMatrix
+            where
+                Rhs: Broadcastable<T>,
+            {
+                // Prepare broadcasted rhs-data
+                let rhs_data = rhs.to_vec(self.rows, self.cols);
+
+                // Pairwise compare
                 let data = self
                     .data
                     .iter()
-                    .zip(&rhs.data)
+                    .cloned()
+                    .zip(rhs_data.into_iter())
                     .map(|(a, b)| a $op b)
                     .collect();
+
                 BoolMatrix::from_vec(data, self.rows, self.cols)
             }
             )*
@@ -208,7 +236,7 @@ macro_rules! impl_elementwise_cmp {
     };
 }
 
-// Invoke it for all five operations:
+// Instantiate element-wise comparison implementations for matrices.
 impl_elementwise_cmp! {
     eq_elementwise => ==,
     lt_elementwise => <,