Make the aview0, aview1, and aview2 free functions be const fns

.github/workflows/ci.yaml

@@ -34,7 +34,7 @@ jobs:
           - stable
           - beta
           - nightly
-          - 1.51.0  # MSRV
+          - 1.57.0  # MSRV
 
     name: tests/${{ matrix.rust }}
     steps:

Cargo.toml

@@ -3,7 +3,7 @@
 name = "ndarray"
 version = "0.15.6"
 edition = "2018"
-rust-version = "1.51"
+rust-version = "1.57"
 authors = [
   "Ulrik Sverdrup \"bluss\"",
   "Jim Turner"

scripts/all-tests.sh

@@ -6,7 +6,7 @@ set -e
 FEATURES=$1
 CHANNEL=$2
 
-if [ "$CHANNEL" = "1.51.0" ]; then
+if [ "$CHANNEL" = "1.57.0" ]; then
     cargo update --package openblas-src --precise 0.10.5
     cargo update --package openblas-build --precise 0.10.5
     cargo update --package once_cell --precise 1.14.0

src/aliases.rs

@@ -7,43 +7,43 @@ use crate::{ArcArray, Array, ArrayView, ArrayViewMut, Ix, IxDynImpl};
 /// Create a zero-dimensional index
 #[allow(non_snake_case)]
 #[inline(always)]
-pub fn Ix0() -> Ix0 {
+pub const fn Ix0() -> Ix0 {
     Dim::new([])
 }
 /// Create a one-dimensional index
 #[allow(non_snake_case)]
 #[inline(always)]
-pub fn Ix1(i0: Ix) -> Ix1 {
+pub const fn Ix1(i0: Ix) -> Ix1 {
     Dim::new([i0])
 }
 /// Create a two-dimensional index
 #[allow(non_snake_case)]
 #[inline(always)]
-pub fn Ix2(i0: Ix, i1: Ix) -> Ix2 {
+pub const fn Ix2(i0: Ix, i1: Ix) -> Ix2 {
     Dim::new([i0, i1])
 }
 /// Create a three-dimensional index
 #[allow(non_snake_case)]
 #[inline(always)]
-pub fn Ix3(i0: Ix, i1: Ix, i2: Ix) -> Ix3 {
+pub const fn Ix3(i0: Ix, i1: Ix, i2: Ix) -> Ix3 {
     Dim::new([i0, i1, i2])
 }
 /// Create a four-dimensional index
 #[allow(non_snake_case)]
 #[inline(always)]
-pub fn Ix4(i0: Ix, i1: Ix, i2: Ix, i3: Ix) -> Ix4 {
+pub const fn Ix4(i0: Ix, i1: Ix, i2: Ix, i3: Ix) -> Ix4 {
     Dim::new([i0, i1, i2, i3])
 }
 /// Create a five-dimensional index
 #[allow(non_snake_case)]
 #[inline(always)]
-pub fn Ix5(i0: Ix, i1: Ix, i2: Ix, i3: Ix, i4: Ix) -> Ix5 {
+pub const fn Ix5(i0: Ix, i1: Ix, i2: Ix, i3: Ix, i4: Ix) -> Ix5 {
     Dim::new([i0, i1, i2, i3, i4])
 }
 /// Create a six-dimensional index
 #[allow(non_snake_case)]
 #[inline(always)]
-pub fn Ix6(i0: Ix, i1: Ix, i2: Ix, i3: Ix, i4: Ix, i5: Ix) -> Ix6 {
+pub const fn Ix6(i0: Ix, i1: Ix, i2: Ix, i3: Ix, i4: Ix, i5: Ix) -> Ix6 {
     Dim::new([i0, i1, i2, i3, i4, i5])
 }
 

src/arraytraits.rs

@@ -307,6 +307,10 @@ pub const ARRAY_FORMAT_VERSION: u8 = 1u8;
 
 // use "raw" form instead of type aliases here so that they show up in docs
 /// Implementation of `ArrayView::from(&S)` where `S` is a slice or sliceable.
+///
+/// **Panics** if the length of the slice overflows `isize`. (This can only
+/// occur if `A` is zero-sized, because slices cannot contain more than
+/// `isize::MAX` number of bytes.)
 impl<'a, A, Slice: ?Sized> From<&'a Slice> for ArrayView<'a, A, Ix1>
 where
     Slice: AsRef<[A]>,
@@ -315,14 +319,7 @@ where
     ///
     /// **Panics** if the slice length is greater than `isize::MAX`.
     fn from(slice: &'a Slice) -> Self {
-        let xs = slice.as_ref();
-        if mem::size_of::<A>() == 0 {
-            assert!(
-                xs.len() <= ::std::isize::MAX as usize,
-                "Slice length must fit in `isize`.",
-            );
-        }
-        unsafe { Self::from_shape_ptr(xs.len(), xs.as_ptr()) }
+        aview1(slice.as_ref())
     }
 }
 
@@ -334,25 +331,7 @@ where
 impl<'a, A, const N: usize> From<&'a [[A; N]]> for ArrayView<'a, A, Ix2> {
     /// Create a two-dimensional read-only array view of the data in `slice`
     fn from(xs: &'a [[A; N]]) -> Self {
-        let cols = N;
-        let rows = xs.len();
-        let dim = Ix2(rows, cols);
-        if size_of::<A>() == 0 {
-            dimension::size_of_shape_checked(&dim)
-                .expect("Product of non-zero axis lengths must not overflow isize.");
-        } else if N == 0 {
-            assert!(
-                xs.len() <= isize::MAX as usize,
-                "Product of non-zero axis lengths must not overflow isize.",
-            );
-        }
-
-        // `cols * rows` is guaranteed to fit in `isize` because we checked that it fits in
-        // `isize::MAX`
-        unsafe {
-            let data = slice::from_raw_parts(xs.as_ptr() as *const A, cols * rows);
-            ArrayView::from_shape_ptr(dim, data.as_ptr())
-        }
+        aview2(xs)
     }
 }
 

src/dimension/dim.rs

@@ -42,7 +42,7 @@ pub struct Dim<I: ?Sized> {
 
 impl<I> Dim<I> {
     /// Private constructor and accessors for Dim
-    pub(crate) fn new(index: I) -> Dim<I> {
+    pub(crate) const fn new(index: I) -> Dim<I> {
         Dim { index }
     }
     #[inline(always)]

src/free_functions.rs

@@ -10,6 +10,7 @@ use alloc::vec;
 #[cfg(not(feature = "std"))]
 use alloc::vec::Vec;
 use std::mem::{forget, size_of};
+use std::ptr::NonNull;
 
 use crate::imp_prelude::*;
 use crate::{dimension, ArcArray1, ArcArray2};
@@ -65,32 +66,105 @@ pub fn rcarr1<A: Clone>(xs: &[A]) -> ArcArray1<A> {
 }
 
 /// Create a zero-dimensional array view borrowing `x`.
-pub fn aview0<A>(x: &A) -> ArrayView0<'_, A> {
-    unsafe { ArrayView::from_shape_ptr(Ix0(), x) }
+pub const fn aview0<A>(x: &A) -> ArrayView0<'_, A> {
+    ArrayBase {
+        data: ViewRepr::new(),
+        // Safe because references are always non-null.
+        ptr: unsafe { NonNull::new_unchecked(x as *const A as *mut A) },
+        dim: Ix0(),
+        strides: Ix0(),
+    }
 }
 
 /// Create a one-dimensional array view with elements borrowing `xs`.
 ///
+/// **Panics** if the length of the slice overflows `isize`. (This can only
+/// occur if `A` is zero-sized, because slices cannot contain more than
+/// `isize::MAX` number of bytes.)
+///
 /// ```
-/// use ndarray::aview1;
+/// use ndarray::{aview1, ArrayView1};
 ///
 /// let data = [1.0; 1024];
 ///
 /// // Create a 2D array view from borrowed data
 /// let a2d = aview1(&data).into_shape((32, 32)).unwrap();
 ///
 /// assert_eq!(a2d.sum(), 1024.0);
+///
+/// // Create a const 1D array view
+/// const C: ArrayView1<'static, f64> = aview1(&[1., 2., 3.]);
+///
+/// assert_eq!(C.sum(), 6.);
 /// ```
-pub fn aview1<A>(xs: &[A]) -> ArrayView1<'_, A> {
-    ArrayView::from(xs)
+pub const fn aview1<A>(xs: &[A]) -> ArrayView1<'_, A> {
+    if size_of::<A>() == 0 {
+        assert!(
+            xs.len() <= isize::MAX as usize,
+            "Slice length must fit in `isize`.",
+        );
+    }
+    ArrayBase {
+        data: ViewRepr::new(),
+        // Safe because references are always non-null.
+        ptr: unsafe { NonNull::new_unchecked(xs.as_ptr() as *mut A) },
+        dim: Ix1(xs.len()),
+        strides: Ix1(1),
+    }
 }
 
 /// Create a two-dimensional array view with elements borrowing `xs`.
 ///
-/// **Panics** if the product of non-zero axis lengths overflows `isize` (This can only occur if A
-/// is zero-sized because slices cannot contain more than `isize::MAX` number of bytes).
-pub fn aview2<A, const N: usize>(xs: &[[A; N]]) -> ArrayView2<'_, A> {
-    ArrayView2::from(xs)
+/// **Panics** if the product of non-zero axis lengths overflows `isize` (This
+/// can only occur if A is zero-sized or if `N` is zero, because slices cannot
+/// contain more than `isize::MAX` number of bytes).
+///
+/// ```
+/// use ndarray::{aview2, ArrayView2};
+///
+/// let data = vec![[1., 2., 3.], [4., 5., 6.]];
+///
+/// let view = aview2(&data);
+/// assert_eq!(view.sum(), 21.);
+///
+/// // Create a const 2D array view
+/// const C: ArrayView2<'static, f64> = aview2(&[[1., 2., 3.], [4., 5., 6.]]);
+/// assert_eq!(C.sum(), 21.);
+/// ```
+pub const fn aview2<A, const N: usize>(xs: &[[A; N]]) -> ArrayView2<'_, A> {
+    let cols = N;
+    let rows = xs.len();
+    if size_of::<A>() == 0 {
+        if let Some(n_elems) = rows.checked_mul(cols) {
+            assert!(
+                rows <= isize::MAX as usize
+                    && cols <= isize::MAX as usize
+                    && n_elems <= isize::MAX as usize,
+                "Product of non-zero axis lengths must not overflow isize.",
+            );
+        } else {
+            panic!("Overflow in number of elements.");
+        }
+    } else if N == 0 {
+        assert!(
+            rows <= isize::MAX as usize,
+            "Product of non-zero axis lengths must not overflow isize.",
+        );
+    }
+    // Safe because references are always non-null.
+    let ptr = unsafe { NonNull::new_unchecked(xs.as_ptr() as *mut A) };
+    let dim = Ix2(rows, cols);
+    let strides = if rows == 0 || cols == 0 {
+        Ix2(0, 0)
+    } else {
+        Ix2(cols, 1)
+    };
+    ArrayBase {
+        data: ViewRepr::new(),
+        ptr,
+        dim,
+        strides,
+    }
 }
 
 /// Create a one-dimensional read-write array view with elements borrowing `xs`.

src/lib.rs

@@ -71,7 +71,7 @@
 //!     needs matching memory layout to be efficient (with some exceptions).
 //!   + Efficient floating point matrix multiplication even for very large
 //!     matrices; can optionally use BLAS to improve it further.
-//! - **Requires Rust 1.51 or later**
+//! - **Requires Rust 1.57 or later**
 //!
 //! ## Crate Feature Flags
 //!
@@ -1450,7 +1450,7 @@ pub struct RawViewRepr<A> {
 
 impl<A> RawViewRepr<A> {
     #[inline(always)]
-    fn new() -> Self {
+    const fn new() -> Self {
         RawViewRepr { ptr: PhantomData }
     }
 }
@@ -1467,7 +1467,7 @@ pub struct ViewRepr<A> {
 
 impl<A> ViewRepr<A> {
     #[inline(always)]
-    fn new() -> Self {
+    const fn new() -> Self {
         ViewRepr { life: PhantomData }
     }
 }