fix: ensure proper cache invalidation

---
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---

Author: kgryte

lib/node_modules/@stdlib/array/base/nested2views/lib/main.js

@@ -23,6 +23,7 @@
 // MODULES //
 
 var setNonEnumerableReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
+var setNonEnumerable = require( '@stdlib/utils/define-nonenumerable-property' );
 var setReadWriteAccessor = require( '@stdlib/utils/define-read-write-accessor' );
 var resolveGetter = require( '@stdlib/array/base/resolve-getter' );
 var accessors = require( '@stdlib/array/base/accessors' );
@@ -99,13 +100,15 @@ function nested2views( arr, fields ) {
 	* @private
 	* @constructor
 	* @param {Collection} arr - nested array
+	* @param {NonNegativeInteger} i - element index
 	* @returns {Datum} datum instance
 	*/
-	function Datum( arr ) {
+	function Datum( arr, i ) {
 		var acc = accessors( arr ).accessors;
-		setNonEnumerableReadOnly( this, '_arr', arr );
-		setNonEnumerableReadOnly( this, '_get', acc[ 0 ] );
-		setNonEnumerableReadOnly( this, '_set', acc[ 1 ] );
+		setNonEnumerable( this, '_arr', arr );
+		setNonEnumerable( this, '_get', acc[ 0 ] );
+		setNonEnumerable( this, '_set', acc[ 1 ] );
+		setNonEnumerableReadOnly( this, '_i', i );
 		return this;
 	}
 
@@ -114,16 +117,37 @@ function nested2views( arr, fields ) {
 		setReadWriteAccessor( Datum.prototype, keys[ i ], getValue( i ), setValue( i ) ); // eslint-disable-line max-len
 	}
 
+	// Define a method for ensuring that cached references are up-to-date:
+	setNonEnumerableReadOnly( Datum.prototype, '_updateCache', updateCache );
+
 	// Ensure that the returned array correctly serializes to JSON:
 	setNonEnumerableReadOnly( Datum.prototype, 'toJSON', toJSON );
 
 	// Create a list of composite views...
 	out = [];
 	for ( i = 0; i < M; i++ ) {
-		out.push( new Datum( oget( arr, i ) ) );
+		out.push( new Datum( oget( arr, i ), i ) );
 	}
 	return out;
 
+	/**
+	* Updates cached references, if necessary.
+	*
+	* @private
+	*/
+	function updateCache() {
+		var acc;
+		var ref;
+
+		ref = oget( arr, this._i );
+		if ( ref !== this._arr ) {
+			acc = accessors( ref ).accessors;
+			this._arr = ref;
+			this._get = acc[ 0 ];
+			this._set = acc[ 1 ];
+		}
+	}
+
 	/**
 	* Returns an accessor for returning the value associated with a field.
 	*
@@ -141,6 +165,7 @@ function nested2views( arr, fields ) {
 		* @returns {*} result
 		*/
 		function get() {
+			this._updateCache();
 			return this._get( this._arr, idx );
 		}
 	}
@@ -162,6 +187,7 @@ function nested2views( arr, fields ) {
 		* @param {*} value - value to set
 		*/
 		function set( value ) {
+			this._updateCache();
 			this._set( this._arr, idx, value );
 		}
 	}

lib/node_modules/@stdlib/array/base/nested2views/test/test.js

@@ -227,3 +227,65 @@ tape( 'the function returns views on the input arrays (accessors)', function tes
 
 	t.end();
 });
+
+tape( 'the function supports outer array mutation (indexed)', function test( t ) {
+	var actual;
+	var fields;
+	var tmp;
+	var x;
+
+	fields = [ 'x', 'y' ];
+
+	x = [ [ 1, 2 ], [ 3, 4 ] ];
+
+	actual = nested2views( x, fields );
+
+	t.strictEqual( actual[ 0 ].x, 1, 'returns expected value' );
+	t.strictEqual( actual[ 0 ].y, 2, 'returns expected value' );
+
+	t.strictEqual( actual[ 1 ].x, 3, 'returns expected value' );
+	t.strictEqual( actual[ 1 ].y, 4, 'returns expected value' );
+
+	tmp = x[ 0 ];
+	x[ 0 ] = x[ 1 ];
+	x[ 1 ] = tmp;
+
+	t.strictEqual( actual[ 0 ].x, 3, 'returns expected value' );
+	t.strictEqual( actual[ 0 ].y, 4, 'returns expected value' );
+
+	t.strictEqual( actual[ 1 ].x, 1, 'returns expected value' );
+	t.strictEqual( actual[ 1 ].y, 2, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function supports outer array mutation (accessors)', function test( t ) {
+	var actual;
+	var fields;
+	var tmp;
+	var x;
+
+	fields = [ 'x', 'y' ];
+
+	x = [ [ 1, 2 ], [ 3, 4 ] ];
+
+	actual = nested2views( toAccessorArray( x ), fields );
+
+	t.strictEqual( actual[ 0 ].x, 1, 'returns expected value' );
+	t.strictEqual( actual[ 0 ].y, 2, 'returns expected value' );
+
+	t.strictEqual( actual[ 1 ].x, 3, 'returns expected value' );
+	t.strictEqual( actual[ 1 ].y, 4, 'returns expected value' );
+
+	tmp = x[ 0 ];
+	x[ 0 ] = x[ 1 ];
+	x[ 1 ] = tmp;
+
+	t.strictEqual( actual[ 0 ].x, 3, 'returns expected value' );
+	t.strictEqual( actual[ 0 ].y, 4, 'returns expected value' );
+
+	t.strictEqual( actual[ 1 ].x, 1, 'returns expected value' );
+	t.strictEqual( actual[ 1 ].y, 2, 'returns expected value' );
+
+	t.end();
+});