From 288587070c33385aa2a621819938b4f6e8c638ff Mon Sep 17 00:00:00 2001
From: Roland Reichwein <Roland.Reichwein@bmw.de>
Date: Sun, 31 May 2026 14:00:51 +0200
Subject: [PATCH] Fix fixed_iterator::operator* return type
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

fixed_iterator::operator* returned value_type by value, so writes like *it = ...
modified a temporary rather than the underlying location. This broke the
iterator’s intended use (e.g., writing to a fixed register/memory location).
Now returning iterator_traits<TIterator>::reference instead (const and
non-const overloads).
---
 include/etl/fixed_iterator.h |  4 ++--
 test/test_fixed_iterator.cpp | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/include/etl/fixed_iterator.h b/include/etl/fixed_iterator.h
index f0ab7609..fb274b6c 100644
--- a/include/etl/fixed_iterator.h
+++ b/include/etl/fixed_iterator.h
@@ -108,7 +108,7 @@ namespace etl
     //***************************************************************************
     /// Dereference operator.
     //***************************************************************************
-    ETL_CONSTEXPR14 typename etl::iterator_traits<TIterator>::value_type operator*()
+    ETL_CONSTEXPR14 typename etl::iterator_traits<TIterator>::reference operator*()
     {
       return *it;
     }
@@ -116,7 +116,7 @@ namespace etl
     //***************************************************************************
     /// Dereference operator.
     //***************************************************************************
-    ETL_CONSTEXPR const typename etl::iterator_traits<TIterator>::value_type operator*() const
+    ETL_CONSTEXPR typename etl::iterator_traits<TIterator>::reference operator*() const
     {
       return *it;
     }
diff --git a/test/test_fixed_iterator.cpp b/test/test_fixed_iterator.cpp
index af6d54a1..72b6c907 100644
--- a/test/test_fixed_iterator.cpp
+++ b/test/test_fixed_iterator.cpp
@@ -229,6 +229,22 @@ namespace
       CHECK(fi1 != fi3);
     }
 
+    //*************************************************************************
+    TEST(test_dereference_write_through)
+    {
+      int                       value = 42;
+      etl::fixed_iterator<int*> fi(&value);
+
+      // Writing through the dereferenced iterator should modify the underlying value.
+      *fi = 99;
+      CHECK_EQUAL(99, value);
+
+      // Increment does nothing, so writing again still targets the same location.
+      ++fi;
+      *fi = 123;
+      CHECK_EQUAL(123, value);
+    }
+
 #if ETL_USING_CPP14
     //*************************************************************************
     TEST(test_fixed_iterator_constexpr_ctor)