AK: Implement reverse iterator for Vector class

Author: https://github.com/guerinoni
Commit: https://github.com/SerenityOS/serenity/commit/b0e74a3fd3
Pull-request: https://github.com/SerenityOS/serenity/pull/12741
Reviewed-by: https://github.com/IdanHo
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/linusg

AK/Vector.h

@@ -13,6 +13,7 @@
 #include <AK/Forward.h>
 #include <AK/Iterator.h>
 #include <AK/Optional.h>
+#include <AK/ReverseIterator.h>
 #include <AK/Span.h>
 #include <AK/StdLibExtras.h>
 #include <AK/Traits.h>
@@ -693,12 +694,15 @@ public:
 
     using ConstIterator = SimpleIterator<Vector const, VisibleType const>;
     using Iterator = SimpleIterator<Vector, VisibleType>;
+    using ReverseIterator = SimpleReverseIterator<Vector, VisibleType>;
 
     ConstIterator begin() const { return ConstIterator::begin(*this); }
     Iterator begin() { return Iterator::begin(*this); }
+    ReverseIterator rbegin() { return ReverseIterator::rbegin(*this); }
 
     ConstIterator end() const { return ConstIterator::end(*this); }
     Iterator end() { return Iterator::end(*this); }
+    ReverseIterator rend() { return ReverseIterator::rend(*this); }
 
     template<typename TUnaryPredicate>
     ConstIterator find_if(TUnaryPredicate&& finder) const

Tests/AK/TestVector.cpp

@@ -533,3 +533,29 @@ TEST_CASE(reference_deletion_should_not_affect_object)
     }
     EXPECT_EQ(times_deleted, 1u);
 }
+
+TEST_CASE(rbegin)
+{
+    Vector<int> v { 1, 2, 3, 4, 5, 6, 7, 8, 0 };
+
+    auto const expected = v.begin() + 4;
+    auto const expected_in_reverse = v.rbegin() + 4;
+    EXPECT_EQ(*expected, *expected_in_reverse);
+}
+
+TEST_CASE(rend)
+{
+    Vector<int> v { 1, 2, 3, 4, 5, 6, 7, 8, 0 };
+
+    const auto expected = v.end() - 5;
+    const auto expected_in_reverse = v.rend() - 5;
+    EXPECT_EQ(*expected, *expected_in_reverse);
+}
+
+TEST_CASE(reverse_loop)
+{
+    Vector<int> v { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+    int index = 9;
+    for (auto rev = v.rbegin(); rev != v.rend(); ++rev)
+        EXPECT_EQ(*rev, index--);
+}