Add Dimension::zero_index_with_ndim()

Author: jturner314

src/dimension/dimension_trait.rs

@@ -156,6 +156,15 @@ pub trait Dimension : Clone + Eq + Debug + Send + Sync + Default +
         Self::default()
     }
 
+    #[doc(hidden)]
+    /// Return an index of same type and with the specified dimensionality.
+    ///
+    /// This method is useful for generalizing over fixed-size and
+    /// variable-size dimension representations.
+    ///
+    /// **Panics** if `Self` has a fixed size that is not `ndim`.
+    fn zero_index_with_ndim(ndim: usize) -> Self;
+
     #[doc(hidden)]
     #[inline]
     fn first_index(&self) -> Option<Self> {
@@ -371,6 +380,11 @@ impl Dimension for Dim<[Ix; 0]> {
     #[inline]
     fn into_pattern(self) -> Self::Pattern { }
     #[inline]
+    fn zero_index_with_ndim(ndim: usize) -> Self {
+        assert_eq!(ndim, 0);
+        Self::default()
+    }
+    #[inline]
     fn next_for(&self, _index: Self) -> Option<Self> {
         None
     }
@@ -402,6 +416,11 @@ impl Dimension for Dim<[Ix; 1]> {
         get!(&self, 0)
     }
     #[inline]
+    fn zero_index_with_ndim(ndim: usize) -> Self {
+        assert_eq!(ndim, 1);
+        Self::default()
+    }
+    #[inline]
     fn next_for(&self, mut index: Self) -> Option<Self> {
         getm!(index, 0) += 1;
         if get!(&index, 0) < get!(self, 0) {
@@ -491,6 +510,11 @@ impl Dimension for Dim<[Ix; 2]> {
     #[inline]
     fn slice_mut(&mut self) -> &mut [Ix] { self.ixm() }
     #[inline]
+    fn zero_index_with_ndim(ndim: usize) -> Self {
+        assert_eq!(ndim, 2);
+        Self::default()
+    }
+    #[inline]
     fn next_for(&self, index: Self) -> Option<Self> {
         let mut i = get!(&index, 0);
         let mut j = get!(&index, 1);
@@ -630,6 +654,12 @@ impl Dimension for Dim<[Ix; 3]> {
         m as usize * n as usize * o as usize
     }
 
+    #[inline]
+    fn zero_index_with_ndim(ndim: usize) -> Self {
+        assert_eq!(ndim, 3);
+        Self::default()
+    }
+
     #[inline]
     fn next_for(&self, index: Self) -> Option<Self> {
         let mut i = get!(&index, 0);
@@ -734,6 +764,11 @@ macro_rules! large_dim {
             #[inline]
             fn slice_mut(&mut self) -> &mut [Ix] { self.ixm() }
             #[inline]
+            fn zero_index_with_ndim(ndim: usize) -> Self {
+                assert_eq!(ndim, $n);
+                Self::default()
+            }
+            #[inline]
             $($insert_axis)*
             #[inline]
             fn try_remove_axis(&self, axis: Axis) -> Self::Smaller {
@@ -786,6 +821,11 @@ impl Dimension for IxDyn
         IxDyn::zeros(self.ndim())
     }
 
+    #[inline]
+    fn zero_index_with_ndim(ndim: usize) -> Self {
+        IxDyn::zeros(ndim)
+    }
+
     #[inline]
     fn insert_axis(&self, axis: Axis) -> Self::Larger {
         debug_assert!(axis.index() <= self.ndim());