[LLVMbugs] [Bug 10218] New: __compressed_pair<int, int> does not compile

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=10218

           Summary: __compressed_pair<int, int> does not compile
           Product: libc++
           Version: unspecified
          Platform: Macintosh
        OS/Version: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
        AssignedTo: hhinnant at apple.com
        ReportedBy: jonathan.sauer at gmx.de
                CC: llvmbugs at cs.uiuc.edu


The following applies to a class internal to libc++; I stumbled upon it while
narrowing down Bug 10191. Still, I thought it might be useful to report it:


template <class _T1, class _T2>
class __libcpp_compressed_pair_imp
{
public:
    typedef _T1 _T1_param;
    typedef _T2 _T2_param;

    __libcpp_compressed_pair_imp();
    __libcpp_compressed_pair_imp(_T1_param __t1, int = 0);
    __libcpp_compressed_pair_imp(_T1_param __t1, _T2_param __t2);
};


int main(int, char**)
{
    __libcpp_compressed_pair_imp<int, int>    f;
}


I isolated this code from the __compressed_pair implementation in <memory>.
When compiling with clang r133996, the following error is generated:


clang.cpp:10:2: error: constructor cannot be redeclared
        __libcpp_compressed_pair_imp(_T1_param __t1, _T2_param __t2);
        ^
clang.cpp:16:41: note: in instantiation of template class
'__libcpp_compressed_pair_imp<int, int>'
      requested here
        __libcpp_compressed_pair_imp<int, int>  f;
                                                ^
clang.cpp:9:5: note: previous declaration is here
    __libcpp_compressed_pair_imp(_T1_param __t1, int = 0);
    ^
1 error generated.


This is because <int> is used both as a way to distinguish between the
constructor for <_T1> and <_T2> as well as <_T2> itself, effectively making
lines A and identical.

I think a private type should be used for the dummy parameters instead of <int>
(if the bug is considered relevant, that is).

I'm using libc++ r133667.

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