Prohibit default construction of function_output_iterator on function pointers.

Default-constructed function_output_iterator with function pointers is unusable
and previously would have contained an uninitialized function pointer.
Disable the default constructor using SFINAE to prevent misuse.

Also reformat code.

include/boost/iterator/function_output_iterator.hpp

@@ -8,69 +8,76 @@
 // 27 Feb 2001   Jeremy Siek
 //      Initial checkin.
 
-#ifndef BOOST_ITERATOR_FUNCTION_OUTPUT_ITERATOR_HPP
-#define BOOST_ITERATOR_FUNCTION_OUTPUT_ITERATOR_HPP
+#ifndef BOOST_ITERATOR_FUNCTION_OUTPUT_ITERATOR_HPP_INCLUDED_
+#define BOOST_ITERATOR_FUNCTION_OUTPUT_ITERATOR_HPP_INCLUDED_
 
 #include <cstddef>
 #include <iterator>
 #include <type_traits>
 
-#include <boost/config.hpp>
-
 namespace boost {
 namespace iterators {
 
-  template <class UnaryFunction>
-  class function_output_iterator {
-  private:
-    typedef function_output_iterator self;
-
-    class output_proxy {
+template< typename UnaryFunction >
+class function_output_iterator
+{
+private:
+    class output_proxy
+    {
     public:
-      explicit output_proxy(UnaryFunction& f) BOOST_NOEXCEPT : m_f(f) { }
-
-      template <class T>
+        explicit output_proxy(UnaryFunction& f) noexcept :
+            m_f(f)
+        {}
 
+        template< typename T >
         typename std::enable_if<
             !std::is_same< typename std::remove_cv< typename std::remove_reference< T >::type >::type, output_proxy >::value,
             output_proxy const&
-      >::type operator=(T&& value) const {
+        >::type operator=(T&& value) const
+        {
             m_f(static_cast< T&& >(value));
             return *this;
         }
 
-      BOOST_DEFAULTED_FUNCTION(output_proxy(output_proxy const& that), BOOST_NOEXCEPT : m_f(that.m_f) {})
-      BOOST_DELETED_FUNCTION(output_proxy& operator=(output_proxy const&))
+        output_proxy(output_proxy const& that) = default;
+        output_proxy& operator=(output_proxy const&) = delete;
 
     private:
         UnaryFunction& m_f;
     };
 
-  public:
-    typedef std::output_iterator_tag iterator_category;
-    typedef void                value_type;
-    typedef std::ptrdiff_t      difference_type;
-    typedef void                pointer;
-    typedef void                reference;
+public:
+    using iterator_category = std::output_iterator_tag;
+    using value_type = void;
+    using difference_type = std::ptrdiff_t;
+    using pointer = void;
+    using reference = void;
 
-    explicit function_output_iterator() {}
+    template<
+        bool Requires = std::is_class< UnaryFunction >::value,
+        typename = typename std::enable_if< Requires >::type
+    >
+    function_output_iterator() :
+        m_f()
+    {}
 
-    explicit function_output_iterator(const UnaryFunction& f)
-      : m_f(f) {}
+    explicit function_output_iterator(UnaryFunction const& f) :
+        m_f(f)
+    {}
 
     output_proxy operator*() { return output_proxy(m_f); }
-    self& operator++() { return *this; }
-    self& operator++(int) { return *this; }
+    function_output_iterator& operator++() { return *this; }
+    function_output_iterator& operator++(int) { return *this; }
 
-  private:
+private:
     UnaryFunction m_f;
-  };
+};
 
-  template <class UnaryFunction>
-  inline function_output_iterator<UnaryFunction>
-  make_function_output_iterator(const UnaryFunction& f = UnaryFunction()) {
-    return function_output_iterator<UnaryFunction>(f);
-  }
+template< typename UnaryFunction >
+inline function_output_iterator< UnaryFunction > make_function_output_iterator(UnaryFunction const& f = UnaryFunction())
+{
+    return function_output_iterator< UnaryFunction >(f);
+}
 
 } // namespace iterators
 
@@ -79,4 +86,4 @@ using iterators::make_function_output_iterator;
 
 } // namespace boost
 
-#endif // BOOST_ITERATOR_FUNCTION_OUTPUT_ITERATOR_HPP
+#endif // BOOST_ITERATOR_FUNCTION_OUTPUT_ITERATOR_HPP_INCLUDED_

test/Jamfile.v2

@@ -58,6 +58,7 @@ test-suite iterator
     [ run function_input_iterator_test.cpp ]
     [ run function_output_iterator_test.cpp ]
     [ compile-fail function_output_iterator_cf.cpp ]
+    [ compile-fail function_output_iterator_def_ctor_cf.cpp ]
 
     [ run generator_iterator_test.cpp ]
 

test/function_output_iterator_def_ctor_cf.cpp

@@ -0,0 +1,14 @@
+// Copyright 2025 (c) Andrey Semashev
+// Distributed under the Boost Software License Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/iterator/function_output_iterator.hpp>
+
+int main()
+{
+    boost::iterators::function_output_iterator< void (*)(int) > it;
+    (void)it;
+
+    return 0;
+}