Add 0-d NDArray support

vecxt/src/NDArrayCheck.scala

@@ -89,14 +89,12 @@ object dimNDArrayCheck:
       end if
 end dimNDArrayCheck
 
-/** shapeCheck validates that the shape is non-empty and all dimensions are > 0. */
+/** shapeCheck validates that all dimensions are > 0. A 0-length shape (0-d array) is valid. */
 object shapeCheck:
   inline def apply(
       shape: Array[Int]
   )(using inline doCheck: BoundsCheck): Unit =
     inline if doCheck then
-      if shape.length == 0 then throw InvalidNDArray("Shape must be non-empty")
-      end if
       var i = 0
       while i < shape.length do
         if shape(i) <= 0 then

vecxt/src/ndarray.scala

@@ -60,6 +60,9 @@ object ndarray:
         end while
         result && data.length == numel
 
+    /** True if this is a 0-dimensional (scalar) NDArray. */
+    lazy val isScalar: Boolean = shape.length == 0
+
     lazy val layout: String =
       s"ndim: $ndim, shape: [${shape.mkString(",")}], strides: [${strides.mkString(",")}], offset: $offset, data length: ${data.length}"
 
@@ -93,6 +96,10 @@ object ndarray:
     )(using inline boundsCheck: BoundsCheck): NDArray[A] =
       new NDArray(data, Array(data.length), Array(1), 0)
 
+    /** Create a 0-dimensional (scalar) NDArray holding a single value. */
+    inline def scalar[A](value: A)(using ct: scala.reflect.ClassTag[A]): NDArray[A] =
+      new NDArray(Array(value), Array.emptyIntArray, Array.emptyIntArray, 0)
+
     inline def zeros[A](
         shape: Array[Int]
     )(using inline boundsCheck: BoundsCheck, oz: OneAndZero[A], ct: scala.reflect.ClassTag[A]): NDArray[A] =