Fix safety of SliceInfo::new

Author: jturner314

src/slice.rs

@@ -307,7 +307,8 @@ impl From<NewAxis> for AxisSliceInfo {
 ///
 /// This trait is unsafe to implement because the implementation must ensure
 /// that `D`, `Self::OutDim`, `self.in_dim()`, and `self.out_ndim()` are
-/// consistent with the `&[AxisSliceInfo]` returned by `self.as_ref()`.
+/// consistent with the `&[AxisSliceInfo]` returned by `self.as_ref()` and that
+/// `self.as_ref()` always returns the same value when called multiple times.
 pub unsafe trait CanSlice<D: Dimension>: AsRef<[AxisSliceInfo]> {
     type OutDim: Dimension;
 
@@ -409,10 +410,13 @@ where
 {
     /// Returns a new `SliceInfo` instance.
     ///
-    /// If you call this method, you are guaranteeing that `in_dim` and
-    /// `out_dim` are consistent with `indices`.
-    ///
     /// **Note:** only unchecked for non-debug builds of `ndarray`.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `in_dim` and `out_dim` are consistent with
+    /// `indices` and that `indices.as_ref()` always returns the same value
+    /// when called multiple times.
     #[doc(hidden)]
     pub unsafe fn new_unchecked(
         indices: T,
@@ -444,7 +448,12 @@ where
     /// Returns a new `SliceInfo` instance.
     ///
     /// Errors if `Din` or `Dout` is not consistent with `indices`.
-    pub fn new(indices: T) -> Result<SliceInfo<T, Din, Dout>, ShapeError> {
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure `indices.as_ref()` always returns the same value
+    /// when called multiple times.
+    pub unsafe fn new(indices: T) -> Result<SliceInfo<T, Din, Dout>, ShapeError> {
         if let Some(in_ndim) = Din::NDIM {
             if in_ndim != indices.as_ref().in_ndim() {
                 return Err(ShapeError::from_kind(ErrorKind::IncompatibleShape));

tests/array.rs

@@ -216,13 +216,15 @@ fn test_slice_dyninput_array_fixed() {
 #[test]
 fn test_slice_array_dyn() {
     let mut arr = Array3::<f64>::zeros((5, 2, 5));
-    let info = &SliceInfo::<_, Ix3, IxDyn>::new([
-        AxisSliceInfo::from(1..),
-        AxisSliceInfo::from(1),
-        AxisSliceInfo::from(NewAxis),
-        AxisSliceInfo::from(..).step_by(2),
-    ])
-    .unwrap();
+    let info = &unsafe {
+        SliceInfo::<_, Ix3, IxDyn>::new([
+            AxisSliceInfo::from(1..),
+            AxisSliceInfo::from(1),
+            AxisSliceInfo::from(NewAxis),
+            AxisSliceInfo::from(..).step_by(2),
+        ])
+        .unwrap()
+    };
     arr.slice(info);
     arr.slice_mut(info);
     arr.view().slice_move(info);
@@ -232,13 +234,15 @@ fn test_slice_array_dyn() {
 #[test]
 fn test_slice_dyninput_array_dyn() {
     let mut arr = Array3::<f64>::zeros((5, 2, 5)).into_dyn();
-    let info = &SliceInfo::<_, Ix3, IxDyn>::new([
-        AxisSliceInfo::from(1..),
-        AxisSliceInfo::from(1),
-        AxisSliceInfo::from(NewAxis),
-        AxisSliceInfo::from(..).step_by(2),
-    ])
-    .unwrap();
+    let info = &unsafe {
+        SliceInfo::<_, Ix3, IxDyn>::new([
+            AxisSliceInfo::from(1..),
+            AxisSliceInfo::from(1),
+            AxisSliceInfo::from(NewAxis),
+            AxisSliceInfo::from(..).step_by(2),
+        ])
+        .unwrap()
+    };
     arr.slice(info);
     arr.slice_mut(info);
     arr.view().slice_move(info);
@@ -248,13 +252,15 @@ fn test_slice_dyninput_array_dyn() {
 #[test]
 fn test_slice_dyninput_vec_fixed() {
     let mut arr = Array3::<f64>::zeros((5, 2, 5)).into_dyn();
-    let info = &SliceInfo::<_, Ix3, Ix3>::new(vec![
-        AxisSliceInfo::from(1..),
-        AxisSliceInfo::from(1),
-        AxisSliceInfo::from(NewAxis),
-        AxisSliceInfo::from(..).step_by(2),
-    ])
-    .unwrap();
+    let info = &unsafe {
+        SliceInfo::<_, Ix3, Ix3>::new(vec![
+            AxisSliceInfo::from(1..),
+            AxisSliceInfo::from(1),
+            AxisSliceInfo::from(NewAxis),
+            AxisSliceInfo::from(..).step_by(2),
+        ])
+        .unwrap()
+    };
     arr.slice(info);
     arr.slice_mut(info);
     arr.view().slice_move(info);
@@ -264,13 +270,15 @@ fn test_slice_dyninput_vec_fixed() {
 #[test]
 fn test_slice_dyninput_vec_dyn() {
     let mut arr = Array3::<f64>::zeros((5, 2, 5)).into_dyn();
-    let info = &SliceInfo::<_, Ix3, IxDyn>::new(vec![
-        AxisSliceInfo::from(1..),
-        AxisSliceInfo::from(1),
-        AxisSliceInfo::from(NewAxis),
-        AxisSliceInfo::from(..).step_by(2),
-    ])
-    .unwrap();
+    let info = &unsafe {
+        SliceInfo::<_, Ix3, IxDyn>::new(vec![
+            AxisSliceInfo::from(1..),
+            AxisSliceInfo::from(1),
+            AxisSliceInfo::from(NewAxis),
+            AxisSliceInfo::from(..).step_by(2),
+        ])
+        .unwrap()
+    };
     arr.slice(info);
     arr.slice_mut(info);
     arr.view().slice_move(info);

tests/oper.rs

@@ -595,7 +595,7 @@ fn scaled_add_3() {
 
                 {
                     let mut av = a.slice_mut(s![..;s1, ..;s2]);
-                    let c = c.slice(&SliceInfo::<_, IxDyn, IxDyn>::new(cslice).unwrap());
+                    let c = c.slice(&unsafe { SliceInfo::<_, IxDyn, IxDyn>::new(cslice).unwrap() });
 
                     let mut answerv = answer.slice_mut(s![..;s1, ..;s2]);
                     answerv += &(beta * &c);