Fixed slice function and added tests for slice

Author: CMCDragonkai

lib/ArrayFixed.js

@@ -96,7 +96,21 @@ class ArrayFixed<item> {
   }
 
   slice (begin: ?number, end: ?number): ArrayFixed<item> {
-    return ArrayFixed.fromArray(this._array.slice(begin, end));
+    if (begin == null) begin = 0;
+    if (end == null) end = this._array.length;
+    if (begin < 0) {
+      begin = Math.max(begin + this._array.length, 0);
+    }
+    if (end < 0) {
+      end = Math.max(end + this._array.length, 0);
+    }
+    let count;
+    if (this._direction) {
+      count = Math.max(this._count - begin, 0) - Math.max(this._count - end, 0);
+    } else {
+      count = Math.max(end - this._count, 0) - Math.max(begin - this._count, 0);
+    }
+    return ArrayFixed.fromArray(this._array.slice(begin, end), count);
   }
 
   splice (

lib/ArrayFixedDense.js

@@ -128,7 +128,25 @@ class ArrayFixedDense<item> extends ArrayFixed<item> {
   }
 
   slice (begin: ?number, end: ?number): ArrayFixedDense<item> {
-    return ArrayFixedDense.fromArray(this._array.slice(begin, end));
+    if (begin == null) begin = 0;
+    if (end == null) end = this._array.length;
+    if (begin < 0) {
+      begin = Math.max(begin + this._array.length, 0);
+    }
+    if (end < 0) {
+      end = Math.max(end + this._array.length, 0);
+    }
+    let count;
+    if (this._direction) {
+      count = Math.max(this._count - begin, 0) - Math.max(this._count - end, 0);
+    } else {
+      count = Math.max(end - this._count, 0) - Math.max(begin - this._count, 0);
+    }
+    return ArrayFixedDense.fromArray(
+      this._array.slice(begin, end),
+      count,
+      this._direction
+    );
   }
 
   splice (

test/ArrayFixed.js

@@ -48,6 +48,27 @@ test('iterator', t => {
   t.deepEqual([...arr], [...arrF]);
 });
 
+test('slice', t => {
+  let arr, slice;
+  arr = new ArrayFixed([1,2,3,4, , ,]);
+  slice = arr.slice(0, arr.count / 2);
+  t.deepEqual(slice.toArray(), [1,2]);
+  slice = arr.slice(arr.count / 2);
+  t.deepEqual(slice.toArray(), [3,4, , ,]);
+  slice = arr.slice(0);
+  t.deepEqual(slice.toArray(), [1,2,3,4, , ,]);
+  slice = arr.slice(-2);
+  t.deepEqual(slice.toArray(), [ , ,]);
+  slice = arr.slice(-3, 4);
+  t.deepEqual(slice.toArray(), [4]);
+  slice = arr.slice(-3, -2);
+  t.deepEqual(slice.toArray(), [4]);
+  slice = arr.slice(2, 1);
+  t.deepEqual(slice.toArray(), []);
+  slice = arr.slice(arr.length);
+  t.deepEqual(slice.toArray(), []);
+});
+
 test('splice', t => {
   const arr = new ArrayFixed([1,2,,4,5,,]);
   t.is(arr.count, 4);

test/ArrayFixedDense.js

@@ -79,6 +79,44 @@ test('unsetting elements', t => {
   t.deepEqual(arr.toArray(), [ ,]);
 });
 
+test('slice', t => {
+  let arr, slice;
+  arr = new ArrayFixedDense([1,2,3,4, , ,]);
+  slice = arr.slice(0, arr.count / 2);
+  t.deepEqual(slice.toArray(), [1,2]);
+  slice = arr.slice(arr.count / 2);
+  t.deepEqual(slice.toArray(), [3,4, , ,]);
+  slice = arr.slice(0);
+  t.deepEqual(slice.toArray(), [1,2,3,4, , ,]);
+  slice = arr.slice(-2);
+  t.deepEqual(slice.toArray(), [ , ,]);
+  slice = arr.slice(-3, 4);
+  t.deepEqual(slice.toArray(), [4]);
+  slice = arr.slice(-3, -2);
+  t.deepEqual(slice.toArray(), [4]);
+  slice = arr.slice(2, 1);
+  t.deepEqual(slice.toArray(), []);
+  slice = arr.slice(arr.length);
+  t.deepEqual(slice.toArray(), []);
+  arr = new ArrayFixedDense([ , ,1,2,3,4], false);
+  slice = arr.slice(0, arr.count / 2);
+  t.deepEqual(slice.toArray(), [ , ,]);
+  slice = arr.slice(arr.count / 2);
+  t.deepEqual(slice.toArray(), [1,2,3,4]);
+  slice = arr.slice(0);
+  t.deepEqual(slice.toArray(), [ , ,1,2,3,4]);
+  slice = arr.slice(-2);
+  t.deepEqual(slice.toArray(), [3,4]);
+  slice = arr.slice(-3, 4);
+  t.deepEqual(slice.toArray(), [2]);
+  slice = arr.slice(-3, -2);
+  t.deepEqual(slice.toArray(), [2]);
+  slice = arr.slice(2, 1);
+  t.deepEqual(slice.toArray(), []);
+  slice = arr.slice(arr.length);
+  t.deepEqual(slice.toArray(), []);
+});
+
 test('splice', t => {
   let arr;
   arr = new ArrayFixedDense([1,2,3,4, , ,]);