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From: Stefan Ring <stefanrin@gmail.com>
Date: Wed, 6 Jan 2021 21:51:30 +0100
Message-ID: <CAAxjCEw2O6YSN0x4F5pXFO1EABhbR98okjpj_u0GU8Apid49Pw@mail.gmail.com>
Subject: Re: Possible bug in gcc-10.2 with non-type template parameter
To: Edward Diener <eldlistmailingz@tropicsoft.com>
Cc: gcc-help <gcc-help@gcc.gnu.org>
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On Mon, Jan 4, 2021 at 9:49 PM Edward Diener
<eldlistmailingz@tropicsoft.com> wrote:
>
> The code, called test_predicate.cpp, simplified from a much more
> elaborate implementation:
>
> template < typename T, T *d >  class atmp { atmp() {} };
>
> template < typename T > struct ast
>      {
>      static T avar;
>      static atmp<T,&avar> acst;
>      };
>
> template < typename T > T ast<T>::avar;
> template < typename T > atmp<T,&ast<T>::avar> ast<T>::acst;
>
> int main()
>     {
>     return 0;
>     }
>
> The command line compile flags for gcc-10.2:
>
> -fvisibility-inlines-hidden -Wno-unused-local-typedefs
> -ftrack-macro-expansion=0 -Wno-unused-variable
> -D_GLIBCXX_USE_CXX11_ABI=1 -Wa,-mbig-obj -m64 -mthreads -O0 -fno-inline
> -Wall -g -fvisibility=hidden -std=c++11 -c
>
> The result:
>
> test_predicate.cpp:10:47: error: conflicting declaration 'atmp<T, (&
> ast<T>::avar)> ast<T>::acst'
>     10 | template < typename T > atmp<T,&ast<T>::avar> ast<T>::acst;
>        |                                               ^~~~~~
> test_predicate.cpp:6:26: note: previous declaration as 'atmp<T, (&
> ast<T>::avar)> ast<T>::acst'
>      6 |     static atmp<T,&avar> acst;
>        |                          ^~~~
>
> The same source compiled with clang-11.0 and VC++14.2 succeeds with no
> error.
>
> Is this s bug in gcc ? If so, is there a known workaround ?

Hmm, I'm not a language lawyer, and the error message does not seem to
make sense, but what happens when you remove the offending line in
your real program?