C++ type equality not recognized under SFINAE context - by Bronek

Status : 

  Fixed<br /><br />
		This item has been fixed in the current or upcoming version of this product.<br /><br />
		A more detailed explanation for the resolution of this particular item may have been provided in the comments section.


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ID 718729 Comments
Status Closed Workarounds
Type Bug Repros 0
Opened 1/15/2012 3:04:51 PM
Access Restriction Public
Moderator Decision Sent to Engineering Team for consideration

Description

Template like the following may fail (under SFINAE context, so it's quiet failure) when both parameters are same type, and type T is a pointer to template specialization

template <typename T, T> struct same_ { typedef void* type; };

Outside of SFINAE context, similar code works as intended.
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Posted by Bronek on 1/16/2012 at 2:30 PM
Actual workaround posted in "Workarounds" tab
Posted by Bronek on 1/16/2012 at 12:55 PM
Ooops, code posted at 16/01/2012 at 12:13 is not working workaround, it disables SFINAE.
Posted by Bronek on 1/16/2012 at 12:13 PM
Thank you - great to know this is fixed!

For those stuck with the current version, here is workaround:

template <typename A> struct testme{};

typedef char true_;
typedef int false_;
template <typename T, T> struct same_ { typedef void* type; };

template <typename A>
struct has_path_
{
typedef testme<int> A::*f;
static false_ select(...);
static true_ select(typename same_<f, &A::path>::type);
};

template <typename A>
struct has_path
{
enum { value = sizeof(has_path_<A>::select(0)) == sizeof(true_) };
};

struct get
{
testme<int> path;
};

int main()
{
int t[(int)has_path<get>::value];
(void)t;
}
Posted by Microsoft on 1/16/2012 at 12:05 PM
Hi:
    A fix for this issue has been checked into the compiler sources. The fix should show up in the next release of Visual C++.

Xiang Fan
Visual C++ Team
Posted by MS-Moderator07 [Feedback Moderator] on 1/15/2012 at 7:12 PM
Thanks for your feedback.

We are rerouting this issue to the appropriate group within the Visual Studio Product Team for triage and resolution. These specialized experts will follow-up with your issue.
Posted by MS-Moderator01 on 1/15/2012 at 3:41 PM
Thank you for your feedback, we are currently reviewing the issue you have submitted. If this issue is urgent, please contact support directly(http://support.microsoft.com)