[llvm-bugs] [Bug 24891] New: std::integral_constant::operator ()() usage in std::tuple::get()

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=24891

            Bug ID: 24891
           Summary: std::integral_constant::operator ()() usage in
                    std::tuple::get()
           Product: clang
           Version: 3.6
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++14
          Assignee: unassignedclangbugs at nondot.org
          Reporter: witosx at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 14917
  --> https://llvm.org/bugs/attachment.cgi?id=14917&action=edit
c++14 source code ilustrating the problem

Clang will comply with "candidate template ignored: invalid
explicitly-specified argument for template parameter '__i'" when trying to
fetch tuple element with std::get when index is given by
std::integral_constant::operator()() called on lvalue/rvalue reference.

Attached stripped down example of source failing to compile. 

Full compilation error:

rafalw at montec-d3 ~/CODE % clang++ -c -std=c++14 integral_constant.cpp 
integral_constant.cpp:17:5: error: no matching function for call to 'get'
    std::get<i()>(tuple);
    ^~~~~~~~~~~~~
integral_constant.cpp:36:5: note: in instantiation of function template
specialization 'get_b<unsigned long, 1>' requested here
    get_b(I{});
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:147:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(std::pair<_Tp1, _Tp2>& __in) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:152:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(std::pair<_Tp1, _Tp2>&& __in) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:157:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(const std::pair<_Tp1, _Tp2>& __in) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:166:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(pair<_Tp, _Up>& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:171:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(const pair<_Tp, _Up>& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:176:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(pair<_Tp, _Up>&& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:181:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(pair<_Up, _Tp>& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:186:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(const pair<_Up, _Tp>& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:191:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(pair<_Up, _Tp>&& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/array:280:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(array<_Tp, _Nm>& __arr) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/array:289:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(array<_Tp, _Nm>&& __arr) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/array:297:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(const array<_Tp, _Nm>& __arr) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:832:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '__i'
    get(tuple<_Elements...>& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:838:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '__i'
    get(const tuple<_Elements...>& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:844:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '__i'
    get(tuple<_Elements...>&& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:867:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(tuple<_Types...>& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:873:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(tuple<_Types...>&& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:879:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(const tuple<_Types...>& __t) noexcept
    ^
integral_constant.cpp:25:5: error: no matching function for call to 'get'
    std::get<i()>(tuple);
    ^~~~~~~~~~~~~
integral_constant.cpp:39:5: note: in instantiation of function template
specialization 'get_c<unsigned long, 1>' requested here
    get_c(I{});
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:147:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(std::pair<_Tp1, _Tp2>& __in) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:152:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(std::pair<_Tp1, _Tp2>&& __in) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:157:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(const std::pair<_Tp1, _Tp2>& __in) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:166:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(pair<_Tp, _Up>& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:171:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(const pair<_Tp, _Up>& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:176:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(pair<_Tp, _Up>&& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:181:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(pair<_Up, _Tp>& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:186:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(const pair<_Up, _Tp>& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/utility:191:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(pair<_Up, _Tp>&& __p) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/array:280:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(array<_Tp, _Nm>& __arr) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/array:289:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(array<_Tp, _Nm>&& __arr) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/array:297:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Int'
    get(const array<_Tp, _Nm>& __arr) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:832:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '__i'
    get(tuple<_Elements...>& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:838:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '__i'
    get(const tuple<_Elements...>& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:844:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '__i'
    get(tuple<_Elements...>&& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:867:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(tuple<_Types...>& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:873:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(tuple<_Types...>&& __t) noexcept
    ^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/tuple:879:5:
note: candidate template ignored:
      invalid explicitly-specified argument for template parameter '_Tp'
    get(const tuple<_Types...>& __t) noexcept
    ^
2 errors generated.

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