Implement std::random_access_iterator_tag

src/ThreadPipeline.h

@@ -78,8 +78,7 @@ template <class T> struct ThreadPipeline {
     Batch() : ring(), begin_(), end_() {}
 
     struct Iterator {
-      // TODO implement random_iterator_tag
+      using iterator_category = std::random_access_iterator_tag;
-      using iterator_category = std::forward_iterator_tag;
       using difference_type = std::ptrdiff_t;
       using value_type = T;
       using pointer = value_type *;
@@ -100,6 +99,40 @@ template <class T> struct ThreadPipeline {
         ++(*this);
         return tmp;
       }
+      Iterator &operator--() {
+        --index;
+        return *this;
+      }
+      Iterator operator--(int) {
+        auto tmp = *this;
+        --(*this);
+        return tmp;
+      }
+      Iterator &operator+=(difference_type n) {
+        index += n;
+        return *this;
+      }
+      Iterator &operator-=(difference_type n) {
+        index -= n;
+        return *this;
+      }
+      Iterator operator+(difference_type n) const {
+        return Iterator(index + n, ring);
+      }
+      Iterator operator-(difference_type n) const {
+        return Iterator(index - n, ring);
+      }
+      difference_type operator-(const Iterator &rhs) const {
+        assert(ring == rhs.ring);
+        return static_cast<difference_type>(index) -
+               static_cast<difference_type>(rhs.index);
+      }
+      reference operator[](difference_type n) const {
+        return (*ring)[(index + n) & (ring->size() - 1)];
+      }
+      friend Iterator operator+(difference_type n, const Iterator &iter) {
+        return iter + n;
+      }
       friend bool operator==(const Iterator &lhs, const Iterator &rhs) {
         assert(lhs.ring == rhs.ring);
         return lhs.index == rhs.index;
@@ -108,6 +141,23 @@ template <class T> struct ThreadPipeline {
         assert(lhs.ring == rhs.ring);
         return lhs.index != rhs.index;
       }
+      friend bool operator<(const Iterator &lhs, const Iterator &rhs) {
+        assert(lhs.ring == rhs.ring);
+        // Handle potential uint32_t wraparound by using signed difference
+        return static_cast<int32_t>(lhs.index - rhs.index) < 0;
+      }
+      friend bool operator<=(const Iterator &lhs, const Iterator &rhs) {
+        assert(lhs.ring == rhs.ring);
+        return static_cast<int32_t>(lhs.index - rhs.index) <= 0;
+      }
+      friend bool operator>(const Iterator &lhs, const Iterator &rhs) {
+        assert(lhs.ring == rhs.ring);
+        return static_cast<int32_t>(lhs.index - rhs.index) > 0;
+      }
+      friend bool operator>=(const Iterator &lhs, const Iterator &rhs) {
+        assert(lhs.ring == rhs.ring);
+        return static_cast<int32_t>(lhs.index - rhs.index) >= 0;
+      }
 
     private:
       Iterator(uint32_t index, std::vector<T> *const ring)