From 507f1d82f6c8d13a04d2dc554124b02e4aea6cbd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20P=C3=A9ron?= <peron.clem@gmail.com>
Date: Wed, 18 Jun 2025 17:22:11 +0200
Subject: [PATCH] graph: fix iterator compatibility since C++17
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Add missing iterator typedefs to custom iterator classes when std::iterator
inheritance is deprecated since C++17.

Signed-off-by: Clément Péron <peron.clem@gmail.com>
---
 ortools/base/proto_enum_utils.h | 13 ++++++++++++-
 ortools/graph/graph.h           |  8 +++++++-
 ortools/graph/iterators.h       | 14 ++++++++++++--
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/ortools/base/proto_enum_utils.h b/ortools/base/proto_enum_utils.h
index a78dd61a72..bdf0331056 100644
--- a/ortools/base/proto_enum_utils.h
+++ b/ortools/base/proto_enum_utils.h
@@ -175,8 +175,19 @@ namespace internal {
 template <typename E>
 class RepeatedEnumView {
  public:
-  class Iterator : public std::iterator<std::input_iterator_tag, E> {
+  class Iterator
+#if __cplusplus < 201703L
+      : public std::iterator<std::input_iterator_tag, E>
+#endif
+  {
    public:
+    using difference_type = ptrdiff_t;
+    using value_type = E;
+#if __cplusplus >= 201703L
+    using iterator_category = std::input_iterator_tag;
+    using pointer = E*;
+    using reference = E&;
+#endif
     explicit Iterator(RepeatedField<int>::const_iterator ptr) : ptr_(ptr) {}
     bool operator==(const Iterator& it) const { return ptr_ == it.ptr_; }
     bool operator!=(const Iterator& it) const { return ptr_ != it.ptr_; }
diff --git a/ortools/graph/graph.h b/ortools/graph/graph.h
index c8b7ef0b83..db3f0e2bcb 100644
--- a/ortools/graph/graph.h
+++ b/ortools/graph/graph.h
@@ -315,7 +315,7 @@ class BaseGraph {
 template <typename Graph, typename ArcIterator, typename PropertyT,
           PropertyT (Graph::*property)(typename Graph::ArcIndex) const>
 class ArcPropertyIterator
-#if __cplusplus < 202002L
+#if __cplusplus < 201703L
     : public std::iterator<std::input_iterator_tag, PropertyT>
 #endif
 {
@@ -324,6 +324,11 @@ class ArcPropertyIterator
   // TODO(b/385094969): This should be `NodeIndex` for integers,
   // `NodeIndex::value_type` for strong signed integer types.
   using difference_type = std::ptrdiff_t;
+#if __cplusplus >= 201703L && __cplusplus < 202002L
+  using iterator_category = std::input_iterator_tag;
+  using pointer = PropertyT*;
+  using reference = PropertyT&;
+#endif
 
   ArcPropertyIterator() = default;
 
@@ -346,6 +351,7 @@ class ArcPropertyIterator
                          const ArcPropertyIterator& r) {
     return l.arc_it_ == r.arc_it_;
   }
+
   friend bool operator!=(const ArcPropertyIterator& l,
                          const ArcPropertyIterator& r) {
     return !(l == r);
diff --git a/ortools/graph/iterators.h b/ortools/graph/iterators.h
index 73f67a07bd..50fd5335b0 100644
--- a/ortools/graph/iterators.h
+++ b/ortools/graph/iterators.h
@@ -124,13 +124,18 @@ class IntegerRangeIterator
 // TODO(b/385094969): In C++17, `std::iterator_traits<Iterator>` required
 // explicitly specifying the iterator category. Remove this when backwards
 // compatibility with C++17 is no longer needed.
-#if __cplusplus < 202002L
+#if __cplusplus < 201703L
     : public std::iterator<std::input_iterator_tag, IntegerType>
 #endif
 {
  public:
   using difference_type = ptrdiff_t;
   using value_type = IntegerType;
+#if __cplusplus >= 201703L && __cplusplus < 202002L
+  using iterator_category = std::input_iterator_tag;
+  using pointer = IntegerType*;
+  using reference = IntegerType&;
+#endif
 
   IntegerRangeIterator() : index_{} {}
 
@@ -243,13 +248,18 @@ class IntegerRange : public BeginEndWrapper<IntegerRangeIterator<IntegerType>> {
 // different iterators with the same index type and sentinel.
 template <typename IndexT, const IndexT& sentinel, typename Tag>
 class ChasingIterator
-#if __cplusplus < 202002L
+#if __cplusplus < 201703L
     : public std::iterator<std::input_iterator_tag, IndexT>
 #endif
 {
  public:
   using difference_type = ptrdiff_t;
   using value_type = IndexT;
+#if __cplusplus >= 201703L && __cplusplus < 202002L
+  using iterator_category = std::input_iterator_tag;
+  using pointer = IndexT*;
+  using reference = IndexT&;
+#endif
 
   ChasingIterator() : index_(sentinel), next_(nullptr) {}