Finished iterator_adaptor tutorial

Added example test code
Rolled forward old counting_iterator abstract for boost docs.


[SVN r21649]

example/node_iterator3.hpp

@@ -0,0 +1,58 @@
+// Copyright David Abrahams 2004. Use, modification and distribution is
+// subject to 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)
+#ifndef NODE_ITERATOR3_DWA2004110_HPP
+# define NODE_ITERATOR3_DWA2004110_HPP
+
+# include "node.hpp"
+# include <boost/iterator/iterator_adaptor.hpp>
+
+# ifndef BOOST_NO_SFINAE
+#  include <boost/type_traits/is_convertible.hpp>
+#  include <boost/utility/enable_if.hpp>
+# endif
+
+template <class Value>
+class node_iter
+  : public boost::iterator_adaptor<
+        node_iter<Value>                // Derived
+      , Value*                          // Base
+      , boost::use_default              // Value
+      , boost::forward_traversal_tag    // CategoryOrTraversal
+    >
+{
+ private:
+    struct enabler {};  // a private type avoids misuse
+
+    typedef boost::iterator_adaptor<
+        node_iter<Value>, Value*, boost::use_default, boost::forward_traversal_tag
+    > super_t;
+    
+ public:
+    node_iter()
+      : super_t(0) {}
+
+    explicit node_iter(Value* p)
+      : super_t(p) {}
+
+    template <class OtherValue>
+    node_iter(
+        node_iter<OtherValue> const& other
+# ifndef BOOST_NO_SFINAE
+      , typename boost::enable_if<
+            boost::is_convertible<OtherValue*,Value*>
+          , enabler
+        >::type = enabler()
+# endif 
+    )
+      : m_node(other.m_node) {}
+
+ private:
+    friend class boost::iterator_core_access;
+    void increment() { this->base_reference() = this->base()->next(); }
+};
+
+typedef node_iter<node_base> node_iterator;
+typedef node_iter<node_base const> node_const_iterator;
+
+#endif // NODE_ITERATOR3_DWA2004110_HPP