Add #69: Let IterableAccessor satisfy ranges::input_range

include/fastgltf/tools.hpp

@@ -471,10 +471,10 @@ class IterableAccessor;
 template <typename ElementType, typename BufferDataAdapter = DefaultBufferDataAdapter>
 class AccessorIterator {
 protected:
- const IterableAccessor<ElementType, BufferDataAdapter>* accessor;
- std::size_t idx;
- std::size_t sparseIdx = 0;
- std::size_t nextSparseIndex = 0;
+ const IterableAccessor<ElementType, BufferDataAdapter>* accessor = nullptr;
+ std::size_t idx = std::numeric_limits<std::size_t>::max();
+ mutable std::size_t sparseIdx = 0;
+ mutable std::size_t nextSparseIndex = 0;
 
 public:
  using value_type = ElementType;
@@ -486,6 +486,8 @@ class AccessorIterator {
  // some things that these come with (e.g. std::distance using operator-).
  using iterator_category = std::random_access_iterator_tag;
 
+ AccessorIterator() = default;
+
  AccessorIterator(const IterableAccessor<ElementType, BufferDataAdapter>* accessor, std::size_t idx = 0)
  : accessor(accessor), idx(idx) {
  if (accessor->accessor.sparse.has_value()) {
@@ -512,7 +514,8 @@ class AccessorIterator {
 
  [[nodiscard]] bool operator==(const AccessorIterator& iterator) const noexcept {
  // We don't compare sparse properties
- return idx == iterator.idx &&
+ return accessor == iterator.accessor &&
+ idx == iterator.idx &&
  accessor->bufferBytes.data() == iterator.accessor->bufferBytes.data() &&
  accessor->stride == iterator.accessor->stride &&
  accessor->componentType == iterator.accessor->componentType;
@@ -522,7 +525,7 @@ class AccessorIterator {
  return !(*this == iterator);
  }
 
- [[nodiscard]] ElementType operator*() noexcept {
+ [[nodiscard]] ElementType operator*() const noexcept {
  if (accessor->accessor.sparse.has_value()) {
  if (idx == nextSparseIndex) {
  // Get the sparse value for this index
@@ -546,6 +549,10 @@ class AccessorIterator {
  }
 };
 
+#if FASTGLTF_HAS_CONCEPTS
+static_assert(std::input_iterator<AccessorIterator<math::fvec4>>, "AccessorIterator needs to satisfy input_iterator");
+#endif
+
 template <typename ElementType, typename BufferDataAdapter = DefaultBufferDataAdapter>
 class IterableAccessor {
  friend class AccessorIterator<ElementType, BufferDataAdapter>;
@@ -602,6 +609,10 @@ class IterableAccessor {
  }
 };
 
+#if FASTGLTF_HAS_CONCEPTS
+static_assert(std::ranges::input_range<IterableAccessor<math::fvec4>>, "IterableAccessor needs to satisfy input_range");
+#endif
+
 FASTGLTF_EXPORT template <typename ElementType, typename BufferDataAdapter = DefaultBufferDataAdapter>
 #if FASTGLTF_HAS_CONCEPTS
 requires Element<ElementType>