Updates ZipIterator to support offsetting and std::next/prev

Author: briancairl

include/mf/zip_iterator.hpp

@@ -85,6 +85,37 @@ template <typename... IteratorTs> class ZipIterator<std::tuple<IteratorTs...>>
     return *this;
   }
 
+  inline std::ptrdiff_t operator-(const ZipIterator& other) const
+  {
+    return std::get<0>(this->ptr_) - std::get<0>(other.ptr_);
+  }
+
+  inline ZipIterator operator-(const std::ptrdiff_t offset) const
+  {
+    ZipIterator result{*this};
+    tuple_for_each([offset](auto& ptr) { ptr -= offset; }, result.ptr_);
+    return result;
+  }
+
+  inline ZipIterator operator+(const std::ptrdiff_t offset) const
+  {
+    ZipIterator result{*this};
+    tuple_for_each([offset](auto& ptr) { ptr += offset; }, result.ptr_);
+    return result;
+  }
+
+  inline ZipIterator& operator-=(const std::ptrdiff_t offset)
+  {
+    tuple_for_each([offset](auto& ptr) { ptr -= offset; }, ptr_);
+    return *this;
+  }
+
+  inline ZipIterator& operator+=(const std::ptrdiff_t offset)
+  {
+    tuple_for_each([offset](auto& ptr) { ptr += offset; }, ptr_);
+    return *this;
+  }
+
   inline ZipIterator& operator--()
   {
     tuple_for_each([](auto& ptr) { --ptr; }, ptr_);

test/unit/zip_iterator.cpp

@@ -69,3 +69,36 @@ TEST(ZipIterator, TraitsNoCommonIteratorCatagory)
 
   ASSERT_TRUE((std::is_same_v<std::iterator_traits<decltype(zip_itr)>::iterator_category, void>));
 }
+
+TEST(ZipIterator, PositiveOffset)
+{
+  const std::string s{"oooo"};  // random access
+  const std::string l{"bbbb"};  // random access
+
+  auto zip_itr_begin = mf::make_zip_iterator(s.begin(), l.begin());
+  auto zip_itr_next = zip_itr_begin + 1;
+
+  ASSERT_EQ(std::distance(zip_itr_begin, zip_itr_next), 1);
+}
+
+TEST(ZipIterator, NegativeOffset)
+{
+  const std::string s{"oooo"};  // random access
+  const std::string l{"bbbb"};  // random access
+
+  auto zip_itr_end = mf::make_zip_iterator(s.end(), l.end());
+  auto zip_itr_prev = zip_itr_end - 1;
+
+  ASSERT_EQ(std::distance(zip_itr_end, zip_itr_prev), -1);
+}
+
+TEST(ZipIterator, StdPrev)
+{
+  const std::string s{"oooo"};  // random access
+  const std::string l{"bbbb"};  // random access
+
+  auto zip_itr_end = mf::make_zip_iterator(s.end(), l.end());
+  auto zip_itr_prev = std::prev(zip_itr_end);
+
+  ASSERT_EQ(std::distance(zip_itr_end, zip_itr_prev), -1);
+}