C++ decltype fails to deduce type

Question

Is decltype really buggy in Visual Studio 2012 or is it actually supposed to be this hard to use?

Example:

namespace ptl
{

    struct Test
    {
            


        

Answer 1

I agree with Dietmar: This is a bug in the compiler. The issue appears to be that decltype cannot be applied to an expression that takes the address of a function template specialization. That is, the following is a minimal repro for this issue:

template <typename>
void f();

typedef decltype(&f<void>) t;

As a workaround, consider applying decltype to the function template specialization directly, then adding * to form the required pointer type:

inline auto ExampleFxn2()
    -> decltype(ptl::static_constructor<ptl::Test, float>)*
{
   return &ptl::static_constructor<ptl::Test, float>;
}

Please consider opening a bug for this on Microsoft Connect and posting a link as a comment here for future readers (or, if you would prefer not to, let me know and I would be happy to open a bug for this issue).

Answer 2

The type of &ptl::static_constructor<ptl::Test, float> can be deduced by decltype(). This looks like a bug in MSVC++. Both clang and gcc agree that the code is fine (assuming #include <new> is added).