[c++] Compiler fails to deduce template parameter. by Cory Nelson

Closed

as Fixed

Type:	Bug
ID:	619198
Opened:	11/4/2010 1:25:24 AM
Access Restriction:	Public

Workaround(s)

view

User(s) can reproduce this bug

The attached reproduction code uses tags and template argument deduction to pull base classes out of a derived class. It is 100% legal C++, and compiles fine in GCC (tested with v4.5.1).

The first use of the "get" function works just as expected, but for some reason the second produces two identical C2784 errors, followed by a single C2782 error. These errors are incorrect -- the template arguments are in no way ambiguous.

Interestingly enough, IntelliSense is able to deduce the types correctly.

Details (expand)

Visual Studio 2010

Compatibility

struct base1 {};
struct base2 {};

struct tag1 {};
struct tag2 {};

template<typename Base, typename Tag>
struct tagged {};

struct test : tagged<base1, tag1>, tagged<base2, tag2> {};

template<typename Tag, typename Base>
inline tagged<Base, Tag>& get(tagged<Base, Tag> &o) { return o; }

int main()
{
    test t;

    get<tag1>(t); // works.
    get<tag2>(t); // fails to compile -- template parameter 'Base' is ambiguous.

    return 0;
}

English

Windows 7

English (US)

the compiler errors out

this standard-compliant code should compile without error.

File Name	Submitted By	Submitted On	File Size
cxxtest.cpp	Cory Nelson	11/4/2010	453 bytes

Posted by Cory Nelson on 2/6/2011 at 5:49 AM

Will this fix be in 2010 SP1, or will we have to wait for whatever is next?

Posted by Microsoft on 11/4/2010 at 2:09 AM

Thanks for your feedback. We are routing 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.

Microsoft