Ticket #4189: transform_iterator.2.patch

boost/iterator/transform_iterator.hpp

@@ -14 +14 @@
 #include <boost/iterator/iterator_categories.hpp>
 #include <boost/mpl/not.hpp>
 #include <boost/mpl/bool.hpp>
+#include <boost/optional.hpp>
 #include <boost/type_traits/function_traits.hpp>
+#include <boost/type_traits/has_trivial_constructor.hpp>
 #include <boost/type_traits/is_const.hpp>
 #include <boost/type_traits/is_class.hpp>
 #include <boost/type_traits/is_function.hpp>
@@ -130 +132 @@
    {}
 
     UnaryFunc functor() const
-      { return m_f; }
+      { return unwrap_functor(m_f); }
 
   private:
     typename super_t::reference dereference() const
-    { return m_f(*this->base()); }
+    { return unwrap_functor(m_f)(*this->base()); }
 
+    UnaryFunc const& unwrap_functor(UnaryFunc const& t) const
+    { return t; }
+
+    UnaryFunc const& unwrap_functor(optional<UnaryFunc> const& t) const
+    { return *t; }
+
+    typedef typename mpl::if_<
+        mpl::and_<
+            is_class<UnaryFunc>
+          , mpl::not_<has_trivial_constructor<UnaryFunc> >
+        >
+      , optional<UnaryFunc>
+      , UnaryFunc
+    >::type unary_functor_type;
+
     // Probably should be the initial base class so it can be
     // optimized away via EBO if it is an empty class.
-    UnaryFunc m_f;
+    unary_functor_type m_f;
   };
 
   template <class UnaryFunc, class Iterator>