added ArrayIterator::Empty

Author: jsteemann

include/velocypack/Iterator.h

@@ -41,8 +41,14 @@ class ArrayIterator : public std::iterator<std::forward_iterator_tag, Slice> {
  public:
   using iterator_category = std::forward_iterator_tag;
 
+  struct Empty {};
+
   ArrayIterator() = delete;
 
+  // optimization for an empty array
+  explicit ArrayIterator(Empty) noexcept
+      : _slice(Slice::emptyArraySlice()), _size(0), _position(0), _current(nullptr), _first(nullptr) {}
+
   explicit ArrayIterator(Slice slice)
       : _slice(slice), _size(0), _position(0), _current(nullptr), _first(nullptr) {
 

tests/testsBuilder.cpp

@@ -3447,7 +3447,7 @@ TEST(BuilderTest, TestBoundariesWithPaddingButContainingNones) {
 
 #if __cplusplus >= 201703L
 TEST(BuilderTest, getSharedSlice) {
-  auto const check = [](Builder& b, bool const isSmall) {
+  auto const check = [](Builder& b, bool const /* isSmall */) {
     auto const slice = b.slice();
     ASSERT_EQ(1, b.buffer().use_count());
     auto const sharedSlice = b.sharedSlice();

tests/testsIterator.cpp

@@ -81,6 +81,20 @@ TEST(IteratorTest, IterateArrayEmpty) {
   Slice s(parser.start());
 
   ArrayIterator it(s);
+  ASSERT_EQ(0U, it.size());
+  ASSERT_FALSE(it.valid());
+
+  ASSERT_VELOCYPACK_EXCEPTION(it.value(), Exception::IndexOutOfBounds);
+
+  it.next();
+  ASSERT_FALSE(it.valid());
+  
+  ASSERT_VELOCYPACK_EXCEPTION((*it), Exception::IndexOutOfBounds);
+}
+
+TEST(IteratorTest, IterateArrayEmptySpecial) {
+  ArrayIterator it(ArrayIterator::Empty{});
+  ASSERT_EQ(0U, it.size());
   ASSERT_FALSE(it.valid());
 
   ASSERT_VELOCYPACK_EXCEPTION(it.value(), Exception::IndexOutOfBounds);
@@ -99,6 +113,7 @@ TEST(IteratorTest, IterateArray) {
   Slice s(parser.start());
 
   ArrayIterator it(s);
+  ASSERT_EQ(8U, it.size());
 
   ASSERT_TRUE(it.valid());
   Slice current = it.value();
@@ -167,6 +182,7 @@ TEST(IteratorTest, IterateArrayForward) {
   Slice s(parser.start());
 
   ArrayIterator it(s);
+  ASSERT_EQ(8U, it.size());
 
   ASSERT_TRUE(it.valid());
   Slice current = it.value();
@@ -228,6 +244,7 @@ TEST(IteratorTest, IterateCompactArrayForward) {
   Slice s(parser.start());
 
   ArrayIterator it(s);
+  ASSERT_EQ(8U, it.size());
 
   ASSERT_TRUE(it.valid());
   Slice current = it.value();
@@ -286,12 +303,14 @@ TEST(IteratorTest, IterateSubArray) {
   Slice s(parser.start());
 
   ArrayIterator it(s);
+  ASSERT_EQ(2U, it.size());
 
   ASSERT_TRUE(it.valid());
   Slice current = it.value();
   ASSERT_TRUE(current.isArray());
 
   ArrayIterator it2(current);
+  ASSERT_EQ(3U, it2.size());
   ASSERT_TRUE(it2.valid());
   Slice sub = it2.value();
   ASSERT_TRUE(sub.isNumber());
@@ -322,6 +341,7 @@ TEST(IteratorTest, IterateSubArray) {
   ASSERT_TRUE(current.isArray());
 
   ArrayIterator it3(current);
+  ASSERT_EQ(2U, it3.size());
 
   ASSERT_TRUE(it3.valid());
   sub = it3.value();
@@ -352,6 +372,7 @@ TEST(IteratorTest, IterateArrayUnsorted) {
   Slice s(parser.start());
 
   ArrayIterator it(s);
+  ASSERT_EQ(8U, it.size());
 
   ASSERT_TRUE(it.valid());
   Slice current = it.value();