Add conversions from &T to &OrderedFloat<T>

Fixes #72.

Author: mbrubeck

src/lib.rs

@@ -61,6 +61,24 @@ impl<T: Float> AsMut<T> for OrderedFloat<T> {
     }
 }
 
+impl<'a, T: Float> From<&'a T> for &'a OrderedFloat<T> {
+    fn from(t: &'a T) -> &'a OrderedFloat<T> {
+        // Safety: OrderedFloat is #[repr(transparent)] and has no invalid values.
+        unsafe {
+            &*(t as *const T as *const OrderedFloat<T>)
+        }
+    }
+}
+
+impl<'a, T: Float> From<&'a mut T> for &'a mut OrderedFloat<T> {
+    fn from(t: &'a mut T) -> &'a mut OrderedFloat<T> {
+        // Safety: OrderedFloat is #[repr(transparent)] and has no invalid values.
+        unsafe {
+            &mut *(t as *mut T as *mut OrderedFloat<T>)
+        }
+    }
+}
+
 impl<T: Float> PartialOrd for OrderedFloat<T> {
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         Some(self.cmp(other))

tests/test.rs

@@ -605,3 +605,20 @@ fn not_nan_panic_safety() {
     assert!(!catch_op(not_nan(0.0), |a| *a /= 0.0).is_nan());
     assert!(!catch_op(not_nan(0.0), |a| *a %= 0.0).is_nan());
 }
+
+#[test]
+fn from_ref() {
+    let f = 1.0f32;
+    let o: &OrderedFloat<f32> = (&f).into();
+    assert_eq!(*o, 1.0f32);
+
+    let mut f = 1.0f64;
+    let o: &OrderedFloat<f64> = (&f).into();
+    assert_eq!(*o, 1.0f64);
+
+    let o: &mut OrderedFloat<f64> = (&mut f).into();
+    assert_eq!(*o, 1.0f64);
+    *o = OrderedFloat(2.0);
+    assert_eq!(*o, 2.0f64);
+    assert_eq!(f, 2.0f64);
+}