Add support for retrieving the arity of a function type without partial

specialization. Document and test this


[SVN r14694]

include/boost/type_traits/function_traits.hpp

@@ -300,6 +300,66 @@ struct function_traits :
 {
 };
 
+#else
+
+namespace detail {
+
+template<int N> 
+struct type_of_size
+{
+  char elements[N];
+};
+
+template<typename R>
+type_of_size<1> function_arity_helper(R (*f)());
+
+template<typename R, typename T1>
+type_of_size<2> function_arity_helper(R (*f)(T1));
+
+template<typename R, typename T1, typename T2>
+type_of_size<3> function_arity_helper(R (*f)(T1, T2));
+
+template<typename R, typename T1, typename T2, typename T3>
+type_of_size<4> function_arity_helper(R (*f)(T1, T2, T3));
+
+template<typename R, typename T1, typename T2, typename T3, typename T4>
+type_of_size<5> function_arity_helper(R (*f)(T1, T2, T3, T4));
+
+template<typename R, typename T1, typename T2, typename T3, typename T4,
+         typename T5>
+type_of_size<6> function_arity_helper(R (*f)(T1, T2, T3, T4, T5));
+
+template<typename R, typename T1, typename T2, typename T3, typename T4,
+         typename T5, typename T6>
+type_of_size<7> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6));
+
+template<typename R, typename T1, typename T2, typename T3, typename T4,
+         typename T5, typename T6, typename T7>
+type_of_size<8> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6, T7));
+
+template<typename R, typename T1, typename T2, typename T3, typename T4,
+         typename T5, typename T6, typename T7, typename T8>
+type_of_size<9> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6, T7, T8));
+
+template<typename R, typename T1, typename T2, typename T3, typename T4,
+         typename T5, typename T6, typename T7, typename T8, typename T9>
+type_of_size<10> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6, T7, T8, 
+                                              T9));
+
+template<typename R, typename T1, typename T2, typename T3, typename T4,
+         typename T5, typename T6, typename T7, typename T8, typename T9,
+         typename T10>
+type_of_size<11> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6, T7, T8, 
+                                              T9, T10));
+} // end namespace detail
+
+// Won't work with references
+template<typename Function>
+struct function_traits
+{
+  BOOST_STATIC_CONSTANT(int, arity = (sizeof(detail::function_arity_helper((Function*)0))-1));
+};
+
 #endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 } // boost
 

index.htm

@@ -839,7 +839,7 @@ properties. </p>
         <td valign="top" width="23%" bgcolor="#C0C0C0"><code>::boost::function_traits&lt;F&gt;::arity</code></td>
         <td valign="top" width="28%" bgcolor="#C0C0C0">Determine the arity of the function type <code>F</code>. </td>
         <td valign="top" width="13%" bgcolor="#C0C0C0">&nbsp;</td>
-        <td width="25%" bgcolor="#C0C0C0">P</td>
+        <td width="25%" bgcolor="#C0C0C0">Without partial specialisation support, this template does not compile for reference types.</td>
         <td valign="top" width="5%">&nbsp;</td>
     </tr>
     <tr>
@@ -975,6 +975,13 @@ template.</p>
         <td valign="top" width="41%" bgcolor="#C0C0C0"><code>&lt;boost/type_traits/object_traits.hpp&gt;</code></td>
         <td valign="top" width="9%">&nbsp;</td>
     </tr>
+    <tr>
+        <td>&nbsp;</td>
+        <td valign="top" bgcolor="#C0C0C0"><code>function_traits</code></td>
+        <td valign="top" bgcolor="#C0C0C0"><code>&lt;boost/type_traits/function_traits.hpp&gt;</code></td>
+        <td>&nbsp;</td>
+    </tr>
+
     <tr>
         <td valign="top" width="7%">&nbsp;</td>
         <td valign="top" width="43%" bgcolor="#C0C0C0"><code>has_trivial_constructor</code></td>

tests/function_traits_test.cpp

@@ -45,11 +45,13 @@ struct is_double<double>
 
 int test_main(int, char*[])
 {
-#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
   typedef int F2(float, double);
 
   typedef boost::function_traits<F2> traits;
 
+  BOOST_TEST(traits::arity == 2);
+
+#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
   BOOST_TEST(is_int<traits::result_type>::value);
   BOOST_TEST(is_float<traits::arg1_type>::value);
   BOOST_TEST(is_double<traits::arg2_type>::value);