feat: add Dimension::from_slice (#1608)

Add a public `from_slice` that returns `None` when the slice length does not match the type's dimensionality (`IxDyn` accepts any length). Now `from_dimension` uses `from_slice`.

Closes #1330

Author: SomeB1oody

src/dimension/dimension_trait.rs

@@ -375,18 +375,24 @@ pub trait Dimension:
         IxDyn(self.slice())
     }
 
+    /// Creates a dimension of this type from a slice of axis lengths.
+    ///
+    /// Returns `None` if the slice length is incompatible with this
+    /// dimension type's dimensionality
+    fn from_slice(ix: &[Ix]) -> Option<Self>
+    {
+        if Self::NDIM.is_some_and(|n| n != ix.len()) {
+            return None;
+        }
+        let mut s = Self::zeros(ix.len());
+        s.slice_mut().copy_from_slice(ix);
+        Some(s)
+    }
+
     #[doc(hidden)]
     fn from_dimension<D2: Dimension>(d: &D2) -> Option<Self>
     {
-        let mut s = Self::default();
-        if s.ndim() == d.ndim() {
-            for i in 0..d.ndim() {
-                s[i] = d[i];
-            }
-            Some(s)
-        } else {
-            None
-        }
+        Self::from_slice(d.slice())
     }
 
     #[doc(hidden)]
@@ -584,15 +590,6 @@ impl Dimension for Dim<[Ix; 1]>
     {
         self.remove_axis(axis)
     }
-
-    fn from_dimension<D2: Dimension>(d: &D2) -> Option<Self>
-    {
-        if 1 == d.ndim() {
-            Some(Ix1(d[0]))
-        } else {
-            None
-        }
-    }
     private_impl! {}
 }
 
@@ -1003,9 +1000,9 @@ impl Dimension for IxDyn
         }
     }
 
-    fn from_dimension<D2: Dimension>(d: &D2) -> Option<Self>
+    fn from_slice(ix: &[Ix]) -> Option<Self>
     {
-        Some(IxDyn(d.slice()))
+        Some(IxDyn(ix))
     }
 
     fn into_dyn(self) -> IxDyn

tests/dimension.rs

@@ -2,7 +2,7 @@
 
 use defmac::defmac;
 
-use ndarray::{arr2, ArcArray, Array, Axis, Dim, Dimension, IxDyn, RemoveAxis};
+use ndarray::{arr2, ArcArray, Array, Axis, Dim, Dimension, Ix0, Ix2, IxDyn, RemoveAxis};
 
 use std::hash::{Hash, Hasher};
 
@@ -360,3 +360,21 @@ fn test_all_ndindex()
     ndindex!(10, 4, 3, 2, 2);
     ndindex!(10, 4, 3, 2, 2, 2);
 }
+
+#[test]
+fn from_slice()
+{
+    assert_eq!(Ix0::from_slice(&[]), Some(Dim([])));
+    assert_eq!(Ix0::from_slice(&[1]), None);
+
+    assert_eq!(Ix2::from_slice(&[2, 3]), Some(Dim([2, 3])));
+    assert_eq!(Ix2::from_slice(&[2]), None);
+    assert_eq!(Ix2::from_slice(&[2, 3, 4]), None);
+
+    assert_eq!(IxDyn::from_slice(&[]), Some(IxDyn(&[])));
+    assert_eq!(IxDyn::from_slice(&[2, 3, 4, 5]), Some(IxDyn(&[2, 3, 4, 5])));
+
+    assert_eq!(Ix2::from_dimension(&IxDyn(&[2, 3])), Some(Dim([2, 3])));
+    assert_eq!(Ix2::from_dimension(&IxDyn(&[2, 3, 4])), None);
+    assert_eq!(IxDyn::from_dimension(&Dim([2, 3])), Some(IxDyn(&[2, 3])));
+}