[Boost-commit] svn:boost r4329

From: jefffaust_at_[hidden]
Date: 2007-05-28 13:25:02

Author: jefffaust
Date: 2007-05-28 13:25:01 EDT (Mon, 28 May 2007)
New Revision: 4329
URL: http://svn.boost.org/trac/boost/changeset/4329

Log:
added

Added:
   sandbox/explore/boost/explore/is_assoc_iter.hpp

Added: sandbox/explore/boost/explore/is_assoc_iter.hpp
==============================================================================
--- (empty file)
+++ sandbox/explore/boost/explore/is_assoc_iter.hpp	2007-05-28 13:25:01 EDT (Mon, 28 May 2007)
@@ -0,0 +1,66 @@
+//
+// is_assoc_iter.hpp - meta function to see if an iterator is for an associative
+//                     container, which we assume is true if value_type is a pair.
+//
+// Copyright (c) 2007 Danny Havenith
+//
+// 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/mpl/bool.hpp>
+#include <boost/mpl/eval_if.hpp>
+
+namespace explore
+{
+    namespace detail
+    {
+        using namespace boost::mpl;
+
+        struct false_type
+        {
+            char member[100];
+        };
+
+        // crude SFINAE-and-sizeof. uses the fact that a pointer to a value type
+        // is probably different from than that of false_type. Cleaning this up would take
+        // some more LOC.
+        template< typename T>
+        typename T::value_type* has_value_func( const T &);
+
+        false_type has_value_func(...);
+
+        template <typename T>
+        T& make_t();
+
+        template< typename T>
+        struct has_value_type : bool_<
+            sizeof(false_type)
+            !=
+            sizeof(has_value_func(make_t<T>()))>
+        {};
+
+        //
+        // returns true if the value_t could be the value_type
+        // of a map of which the iterator matches iterator_t
+        //
+        template<typename T>
+        struct is_pair : false_ {};
+
+        template<typename T1, typename T2>
+        struct is_pair<std::pair<T1, T2> > : true_ {};
+
+        template<typename T>
+        struct value_type_is_pair : is_pair<typename T::value_type> {};
+    }
+
+    // an associative iterator has a value type of pair<>
+    template <typename T>
+    struct is_assoc_iter :
+        eval_if<
+            detail::has_value_type<T>,
+            detail::value_type_is_pair<T>,
+            false_
+        > {};
+}
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