From e968c3312b8edffa75f9d6c109aeddedb7b6436d Mon Sep 17 00:00:00 2001
From: Andrey Semashev <andrey.semashev@gmail.com>
Date: Mon, 9 Jun 2025 04:41:53 +0300
Subject: [PATCH] Forward dereferencing operators in operator_brackets_proxy.

This allows for expressions like it[n]->foo() and (*it[n]).foo() to compile.
---
 include/boost/iterator/iterator_facade.hpp | 15 ++++++++++++++-
 test/iterator_adaptor_test.cpp             | 10 ++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/include/boost/iterator/iterator_facade.hpp b/include/boost/iterator/iterator_facade.hpp
index 0604b3c..0c6b356 100644
--- a/include/boost/iterator/iterator_facade.hpp
+++ b/include/boost/iterator/iterator_facade.hpp
@@ -365,12 +365,25 @@ public:
             typename std::remove_cv< typename std::remove_reference< T >::type >::type
         >::value,
         operator_brackets_proxy&
-    >::type operator= (T&& val) noexcept(std::is_nothrow_assignable< reference, T&& >::value)
+    >::type operator= (T&& val) noexcept(noexcept(*std::declval< Iterator const& >() = std::declval< T&& >()))
     {
         *m_iter = static_cast< T&& >(val);
         return *this;
     }
 
+    // Provides it[n]->foo(). Leverages chaining of operator->.
+    reference operator->() const noexcept(noexcept(*std::declval< Iterator const& >()))
+    {
+        return *m_iter;
+    }
+
+    // Provides (*it[n]).foo()
+    template< typename Ref = reference, typename Result = decltype(*std::declval< Ref >()) >
+    Result operator*() const noexcept(noexcept(**std::declval< Iterator const& >()))
+    {
+        return **m_iter;
+    }
+
 private:
     Iterator m_iter;
 };
diff --git a/test/iterator_adaptor_test.cpp b/test/iterator_adaptor_test.cpp
index d237ac4..dc67e2a 100644
--- a/test/iterator_adaptor_test.cpp
+++ b/test/iterator_adaptor_test.cpp
@@ -189,6 +189,16 @@ main()
     boost::const_nonconst_iterator_test(i, ++j);
   }
 
+  // Test that operator_brackets_proxy forwards operator-> and operator*
+  {
+    dummyT* ptr_array[] = { array + 0, array + 1, array + 2,
+                            array + 3, array + 4, array + 5 };
+
+    ptr_iterator<dummyT*> i(ptr_array);
+    BOOST_TEST_EQ(i[2]->foo(), 2);
+    BOOST_TEST_EQ((*i[2]).foo(), 2);
+  }
+
   int test;
   // Test the iterator_traits
   {