Data commit

Task/Metaprogramming/Rust/metaprogramming.rust

@@ -0,0 +1,58 @@
+// dry.rs
+use std::ops::{Add, Mul, Sub};
+
+macro_rules! assert_equal_len {
+    // The `tt` (token tree) designator is used for
+    // operators and tokens.
+    ($a:ident, $b: ident, $func:ident, $op:tt) => (
+        assert!($a.len() == $b.len(),
+                "{:?}: dimension mismatch: {:?} {:?} {:?}",
+                stringify!($func),
+                ($a.len(),),
+                stringify!($op),
+                ($b.len(),));
+    )
+}
+
+macro_rules! op {
+    ($func:ident, $bound:ident, $op:tt, $method:ident) => (
+        fn $func<T: $bound<T, Output=T> + Copy>(xs: &mut Vec<T>, ys: &Vec<T>) {
+            assert_equal_len!(xs, ys, $func, $op);
+
+            for (x, y) in xs.iter_mut().zip(ys.iter()) {
+                *x = $bound::$method(*x, *y);
+                // *x = x.$method(*y);
+            }
+        }
+    )
+}
+
+// Implement `add_assign`, `mul_assign`, and `sub_assign` functions.
+op!(add_assign, Add, +=, add);
+op!(mul_assign, Mul, *=, mul);
+op!(sub_assign, Sub, -=, sub);
+
+mod test {
+    use std::iter;
+    macro_rules! test {
+        ($func: ident, $x:expr, $y:expr, $z:expr) => {
+            #[test]
+            fn $func() {
+                for size in 0usize..10 {
+                    let mut x: Vec<_> = iter::repeat($x).take(size).collect();
+                    let y: Vec<_> = iter::repeat($y).take(size).collect();
+                    let z: Vec<_> = iter::repeat($z).take(size).collect();
+
+                    super::$func(&mut x, &y);
+
+                    assert_eq!(x, z);
+                }
+            }
+        }
+    }
+
+    // Test `add_assign`, `mul_assign` and `sub_assign`
+    test!(add_assign, 1u32, 2u32, 3u32);
+    test!(mul_assign, 2u32, 3u32, 6u32);
+    test!(sub_assign, 3u32, 2u32, 1u32);
+}