Ticket #7343: djw_result_of_sfinae.patch

boost/utility/detail/result_of_iterate.hpp

@@ -51 +51 @@
             typename remove_cv<F>::type(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)), false
           >
         , detail::cpp0x_result_of_impl<
-              F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T))
+              F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)), true
           >
       >::type
 {};
@@ -60 +60 @@
 
 template<typename F BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
          BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),typename T)>
-struct cpp0x_result_of_impl<F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T))>
+class is_callable<F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T))> {
+    typedef char (&pass)[1];
+    typedef char (&fail)[2];
+
+    template<typename G BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
+             BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),typename S)>
+    struct sub {};
+
+    template<typename G BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
+             BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),typename S)>
+    static pass test(sub<G BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
+                         BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),S)>
+                   , boost::remove_reference<
+                          decltype(
+                              boost::declval<G>()(
+                                  BOOST_PP_ENUM_BINARY_PARAMS(BOOST_PP_ITERATION(), declval<S, >() BOOST_PP_INTERCEPT)
+                              )
+                          )
+                      >* x = 0);
+    static fail test(...);
+
+public:
+    const static bool value = sizeof(pass) == sizeof(test(sub<F BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
+                                                              BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)
+                                                          >()));
+    typedef typename boost::mpl::bool_<value>::type type;
+};
+
+template<typename F BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
+         BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),typename T)>
+struct cpp0x_result_of_impl<F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)), true>
+    : lazy_enable_if<
+          is_callable<F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T))>
+        , cpp0x_result_of_impl<F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)), false>
+      >
+{};
+
+template<typename F BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
+         BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),typename T)>
+struct cpp0x_result_of_impl<F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)), false>
 {
   typedef decltype(
     boost::declval<F>()(

boost/utility/result_of.hpp

@@ -24 +24 @@
 #include <boost/type_traits/is_pointer.hpp>
 #include <boost/type_traits/is_member_function_pointer.hpp>
 #include <boost/type_traits/remove_cv.hpp>
+#include <boost/type_traits/remove_reference.hpp>
 #include <boost/utility/declval.hpp>
+#include <boost/utility/enable_if.hpp>
 
 #ifndef BOOST_RESULT_OF_NUM_ARGS
 #  define BOOST_RESULT_OF_NUM_ARGS 16
@@ -58 +60 @@
 
 BOOST_MPL_HAS_XXX_TRAIT_DEF(result_type)
 
+template<typename F> struct is_callable;
+
 template<typename F, typename FArgs, bool HasResultType> struct tr1_result_of_impl;
-template<typename F> struct cpp0x_result_of_impl;
+template<typename F, bool> struct cpp0x_result_of_impl;
 
 template<typename F>
 struct result_of_void_impl

libs/utility/test/result_of_test.cpp

@@ -129 +129 @@
 #endif
 };
 
+// sfinae_tests are derived from example code from Joel de Guzman,
+// which demonstrated the interaction between result_of and SFINAE.
+template <typename F, typename Arg>
+typename boost::result_of<F(Arg const&)>::type
+sfinae_test(F f, Arg const& arg)
+{
+    return f(arg);
+}
+
+template <typename F, typename Arg>
+typename boost::result_of<F(Arg&)>::type
+sfinae_test(F f, Arg& arg)
+{
+    return f(arg);
+}
+
+int sfinae_test_f(int& i)
+{
+    return i;
+}
+
 struct X {};
 
 int main()
@@ -268 +289 @@
 #endif
 #endif
 
+#if defined(BOOST_RESULT_OF_USE_DECLTYPE)
+  int i = 123;
+  sfinae_test(sfinae_test_f, i);
+#endif // defined(BOOST_RESULT_OF_USE_DECLTYPE)
+
   return 0;
 }