[result_of] Test fails on clang trunk and gcc-4.7

[Michel Morin]

In C++11, when a function call expression EXPR is a prvalue of non-class types, decltype(EXPR) does not have cv-qualifiers. This is because

• decltype(EXPR)is the type of EXPR when a function call expression EXPR is a prvalue;
• a prvalue of non-class types is never cv-qualified.

So, for "const int f();", decltype(f()) is int.

Because this rule was introduced at the last minute of the C++11 standardization process, only a few compilers implement it for now: clang trunk (which will be clang-3.1) and gcc-4.7. On those compilers in a C++11 mode, the test fails with the following errors.

1. result_of_test.cpp:210:3: error: static assertion failed:

   (is_same<result_of<const
   result_of_member_function_template(double)>::type, const
   double>::value)
   

2. result_of_test.cpp:211:3: error: static assertion failed:

   (is_same<result_of<volatile
   result_of_member_function_template(double)>::type, volatile
   double>::value)
   

3. result_of_test.cpp:212:3: error: static assertion failed:

   (is_same<result_of<const volatile
   result_of_member_function_template(double)>::type, const volatile
   double>::value)
   

4. result_of_test.cpp:239:3: error: static assertion failed:

   (is_same<result_of<const volatile
   no_result_type_or_result_of(void)>::type, const unsigned
   short>::value)
   

5. result_of_test.cpp:244:3: error: static assertion failed:

   (is_same<result_of<const volatile
   no_result_type_or_result_of_template<void>(void)>::type, const
   unsigned short>::value)
   

[Daniel Walker]

These test cases are checking that result_of uses the appropriate operator() when there are cv-overloads by using cv-qualification on the return type as a flag. I replaced the return types with a wrapper, cv_overoad_check, that is used to signal which overload was used. Fixed in [80352].

[Michel Morin]

Confirmed the fix. The test ran fine on gcc 4.7, 4.8 (experimental) and clang 3.1, 3.2 (trunk). Thanks for the fix, Daniel.