From e4eaeeac4482f3b48882afba01e0514ac4b715af Mon Sep 17 00:00:00 2001
From: Andrey Semashev <andrey.semashev@gmail.com>
Date: Fri, 11 Oct 2024 00:26:30 +0300
Subject: [PATCH] Make function_output_iterator compliant with
 std::output_iterator concept.

Fixes https://github.com/boostorg/iterator/issues/85.
Closes https://github.com/boostorg/iterator/pull/87.
---
 include/boost/iterator/function_output_iterator.hpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/boost/iterator/function_output_iterator.hpp b/include/boost/iterator/function_output_iterator.hpp
index b59cbc9..eeb8ddf 100644
--- a/include/boost/iterator/function_output_iterator.hpp
+++ b/include/boost/iterator/function_output_iterator.hpp
@@ -11,6 +11,7 @@
 #ifndef BOOST_ITERATOR_FUNCTION_OUTPUT_ITERATOR_HPP
 #define BOOST_ITERATOR_FUNCTION_OUTPUT_ITERATOR_HPP
 
+#include <cstddef>
 #include <iterator>
 #include <boost/config.hpp>
 #include <boost/core/enable_if.hpp>
@@ -62,7 +63,7 @@ namespace iterators {
   public:
     typedef std::output_iterator_tag iterator_category;
     typedef void                value_type;
-    typedef void                difference_type;
+    typedef std::ptrdiff_t      difference_type;
     typedef void                pointer;
     typedef void                reference;