fix #364 -- x[.ellipsis] returns self instead of a "copy" (#367)

Author: davidkoski

Source/MLX/MLXArray+Indexing.swift

@@ -532,7 +532,9 @@ func getItem(src: MLXArray, operation: MLXArrayIndexOperation, stream: StreamOrD
 {
     switch operation {
     case .ellipsis:
-        return src
+        // let y = x[.elllipsis] -- this should be a "copy", e.g. a full range
+        // slice.  getItemND() handles that, so fall back to it
+        return getItemND(src: src, operations: [operation], stream: stream)
 
     case .newAxis:
         return src.expandedDimensions(axis: 0, stream: stream)

Tests/MLXTests/MLXArray+IndexingTests.swift

@@ -662,4 +662,18 @@ class MLXArrayIndexingTests: XCTestCase {
         assertEqual(b, expected)
     }
 
+    public func testCopyEllipsis() {
+        // https://github.com/ml-explore/mlx-swift/issues/364
+        let x = arange(0, 12).reshaped([3, 4])
+
+        // this should produce an independent copy of x -- they share the same backing
+        // but if y is mutated then x should have reference to the original values
+        let y = x[.ellipsis]
+
+        y[.ellipsis, 1] *= 10
+
+        // x and y should be different
+        XCTAssertFalse(x.allClose(y).all().item())
+    }
+
 }