Moved generator_iterator.hpp in iterator directory and modernized.

generator_iterator now uses decltype approach to deduce value and reference
types instead of the legacy result_type typedef, which was required to be
defined by the generator function.

The default constructor of generator_iterator now value initializes its
data members to avoid using uninitialized data.

doc/generator_iterator.htm

@@ -15,7 +15,7 @@
   <h1>Generator Iterator Adaptor</h1>
 
   <p>Defined in header <a href=
-  "../../boost/generator_iterator.hpp">boost/generator_iterator.hpp</a></p>
+  "../../boost/iterator/generator_iterator.hpp">boost/iterator/generator_iterator.hpp</a></p>
 
   <p>The generator iterator adaptor makes it easier to create custom input
   iterators from 0-ary functions and function objects. The adaptor takes a
@@ -33,9 +33,7 @@
   <blockquote>
     <pre>
 namespace boost {
-  template &lt;class Generator&gt;
+namespace iterators {
-  class generator_iterator_policies;
-
   template &lt;class Generator&gt;
   class generator_iterator_generator;
 
@@ -43,6 +41,7 @@ namespace boost {
   typename generator_iterator_generator&lt;Generator&gt;::type
   make_generator_iterator(Generator &amp; gen);
 }
+}
 </pre>
   </blockquote>
   <hr>
@@ -60,8 +59,8 @@ template &lt;class Generator&gt;
 class generator_iterator_generator
 {
 public:
-  typedef <i>unspecified</i> type; // the resulting generator iterator type 
+  using type = <i>unspecified</i>; // the resulting generator iterator type
-}
+};
 </pre>
 
   <h3>Template Parameters</h3>
@@ -78,8 +77,8 @@ public:
       "http://www.sgi.com/tech/stl/Generator.html">Generator</a></tt></td>
 
       <td>The generator (0-ary function object) type being wrapped. The
-      return type of the function must be defined as
+      return type of the function is deduced automatically from its
-      <tt>Generator::result_type</tt>. The function object must be a model of
+      <tt>operator()</tt>. The function object must be a model of
       <a href=
       "http://www.sgi.com/tech/stl/Generator.html">Generator</a>.</td>
     </tr>
@@ -122,14 +121,14 @@ make_generator_iterator(Generator &amp; gen);
   <blockquote>
     <pre>
 #include &lt;iostream&gt;
-#include &lt;boost/generator_iterator.hpp&gt;
+#include &lt;boost/iterators/generator_iterator.hpp&gt;
 
 class my_generator
 {
 public:
-  typedef int result_type;
+  using result_type = int;
   my_generator() : state(0) { }
-  int operator()() { return ++state; }
+  result_type operator()() { return ++state; }
 private:
   int state;
 };
@@ -137,7 +136,7 @@ private:
 int main()
 {
   my_generator gen;
-  boost::generator_iterator_generator&lt;my_generator&gt;::type it = boost::make_generator_iterator(gen);
+  auto it = boost::iterators::make_generator_iterator(gen);
   for(int i = 0; i &lt; 10; ++i, ++it)
     std::cout &lt;&lt; *it &lt;&lt; std::endl;
 }

include/boost/generator_iterator.hpp

@@ -1,85 +1,14 @@
-// (C) Copyright Jens Maurer 2001.
+// (C) Copyright Andrey Semashev 2025.
 // 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)
-//
-// Revision History:
-
-// 15 Nov 2001   Jens Maurer
-//      created.
-
-//  See http://www.boost.org/libs/utility/iterator_adaptors.htm for documentation.
 
 #ifndef BOOST_ITERATOR_ADAPTOR_GENERATOR_ITERATOR_HPP
 #define BOOST_ITERATOR_ADAPTOR_GENERATOR_ITERATOR_HPP
 
-#include <boost/iterator/iterator_facade.hpp>
+// This is a deprecated header left for backward compatibility.
-#include <boost/ref.hpp>
+// Please use <boost/iterator/generator_iterator.hpp> instead.
 
-namespace boost {
+#include <boost/iterator/generator_iterator.hpp>
-namespace iterators {
-
-template<class Generator>
-class generator_iterator
-  : public iterator_facade<
-        generator_iterator<Generator>
-      , typename Generator::result_type
-      , single_pass_traversal_tag
-      , typename Generator::result_type const&
-    >
-{
-    typedef iterator_facade<
-        generator_iterator<Generator>
-      , typename Generator::result_type
-      , single_pass_traversal_tag
-      , typename Generator::result_type const&
-    > super_t;
-
- public:
-    generator_iterator() {}
-    generator_iterator(Generator* g) : m_g(g), m_value((*m_g)()) {}
-
-    void increment()
-    {
-        m_value = (*m_g)();
-    }
-
-    const typename Generator::result_type&
-    dereference() const
-    {
-        return m_value;
-    }
-
-    bool equal(generator_iterator const& y) const
-    {
-        return this->m_g == y.m_g && this->m_value == y.m_value;
-    }
-
- private:
-    Generator* m_g;
-    typename Generator::result_type m_value;
-};
-
-template<class Generator>
-struct generator_iterator_generator
-{
-  typedef generator_iterator<Generator> type;
-};
-
-template <class Generator>
-inline generator_iterator<Generator>
-make_generator_iterator(Generator& gen)
-{
-  typedef generator_iterator<Generator> result_t;
-  return result_t(&gen);
-}
-
-} // namespace iterators
-
-using iterators::generator_iterator;
-using iterators::generator_iterator_generator;
-using iterators::make_generator_iterator;
-
-} // namespace boost
 
 #endif // BOOST_ITERATOR_ADAPTOR_GENERATOR_ITERATOR_HPP

include/boost/iterator/generator_iterator.hpp

@@ -0,0 +1,96 @@
+// (C) Copyright Jens Maurer 2001.
+// 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)
+//
+// Revision History:
+
+// 15 Nov 2001   Jens Maurer
+//      created.
+
+//  See http://www.boost.org/libs/utility/iterator_adaptors.htm for documentation.
+
+#ifndef BOOST_ITERATOR_GENERATOR_ITERATOR_HPP_INCLUDED_
+#define BOOST_ITERATOR_GENERATOR_ITERATOR_HPP_INCLUDED_
+
+#include <memory>
+#include <type_traits>
+
+#include <boost/iterator/iterator_facade.hpp>
+#include <boost/iterator/iterator_categories.hpp>
+
+namespace boost {
+namespace iterators {
+
+template< typename Generator >
+class generator_iterator :
+    public iterator_facade<
+        generator_iterator< Generator >,
+        decltype(std::declval< Generator& >()()),
+        single_pass_traversal_tag,
+        decltype(std::declval< Generator& >()()) const&
+    >
+{
+    friend class iterator_core_access;
+
+private:
+    using super_t = iterator_facade<
+        generator_iterator< Generator >,
+        decltype(std::declval< Generator& >()()),
+        single_pass_traversal_tag,
+        decltype(std::declval< Generator& >()()) const&
+    >;
+
+public:
+    generator_iterator() :
+        m_g(nullptr),
+        m_value()
+    {}
+
+    generator_iterator(Generator* g) :
+        m_g(g),
+        m_value((*m_g)())
+    {}
+
+private:
+    void increment()
+    {
+        m_value = (*m_g)();
+    }
+
+    typename super_t::reference dereference() const
+    {
+        return m_value;
+    }
+
+    bool equal(generator_iterator const& y) const
+    {
+        return m_g == y.m_g && m_value == y.m_value;
+    }
+
+private:
+    Generator* m_g;
+    typename Generator::result_type m_value;
+};
+
+template< typename Generator >
+struct generator_iterator_generator
+{
+    using type = generator_iterator< Generator >;
+};
+
+template< typename Generator >
+inline generator_iterator< Generator > make_generator_iterator(Generator& gen)
+{
+    return generator_iterator< Generator >(std::addressof(gen));
+}
+
+} // namespace iterators
+
+using iterators::generator_iterator;
+using iterators::generator_iterator_generator;
+using iterators::make_generator_iterator;
+
+} // namespace boost
+
+#endif // BOOST_ITERATOR_GENERATOR_ITERATOR_HPP_INCLUDED_

test/generator_iterator_test.cpp

@@ -6,7 +6,7 @@
 // http://www.boost.org/LICENSE_1_0.txt
 //
 
-#include <boost/generator_iterator.hpp>
+#include <boost/iterator/generator_iterator.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <algorithm>
 

test/test_cmake/main.cpp

@@ -4,7 +4,6 @@
 //  See accompanying file LICENSE_1_0.txt or copy at
 //  https://www.boost.org/LICENSE_1_0.txt)
 
-#include <boost/generator_iterator.hpp>
 #include <boost/indirect_reference.hpp>
 #include <boost/next_prior.hpp>
 #include <boost/pointee.hpp>
@@ -15,6 +14,7 @@
 #include <boost/iterator/filter_iterator.hpp>
 #include <boost/iterator/function_input_iterator.hpp>
 #include <boost/iterator/function_output_iterator.hpp>
+#include <boost/iterator/generator_iterator.hpp>
 #include <boost/iterator/indirect_iterator.hpp>
 #include <boost/iterator/interoperable.hpp>
 #include <boost/iterator/is_iterator.hpp>