[GitHub] [arrow] kou commented on pull request #13874: ARROW-17408: [c++] Fixing C++20 compile warning using operator==(const T&, const T&)

[GitBox <gi...@apache.org>]

kou commented on PR #13874:
URL: https://github.com/apache/arrow/pull/13874#issuecomment-1214676146

   It seems that this breaks VC++ CI: https://ci.appveyor.com/project/ApacheSoftwareFoundation/arrow/builds/44467048/job/2tamgyjibu9kuqvi
   
   ```text
   C:\projects\arrow\cpp\src\arrow/util/compare.h(55): error C2593: 'operator ==' is ambiguous
   C:\projects\arrow\cpp\src\arrow/util/compare.h(54): note: could be 'bool arrow::util::EqualityComparable<arrow::Scalar>::operator ==(const T &) const'
           with
           [
               T=arrow::Scalar
           ]
   C:\projects\arrow\cpp\src\arrow/util/compare.h(57): note: or       'bool arrow::util::operator ==(const T &,const T &)' [found using argument-dependent lookup]
           with
           [
               T=arrow::Scalar
           ]
   C:\projects\arrow\cpp\src\arrow/util/compare.h(55): note: while trying to match the argument list '(const T, const T)'
           with
           [
               T=arrow::Scalar
           ]
   C:\projects\arrow\cpp\src\arrow/util/compare.h(55): note: while compiling class template member function 'bool arrow::util::EqualityComparable<arrow::Scalar>::operator !=(const T &) const'
           with
           [
               T=arrow::Scalar
           ]
   C:\projects\arrow\cpp\src\arrow/scalar.h(53): note: see reference to class template instantiation 'arrow::util::EqualityComparable<arrow::Scalar>' being compiled
   ```
   
   Could you also add a C++20 CI job?
   
   ```diff
   diff --git a/dev/tasks/tasks.yml b/dev/tasks/tasks.yml
   index 7ecc610224..068c956dc8 100644
   --- a/dev/tasks/tasks.yml
   +++ b/dev/tasks/tasks.yml
   @@ -1211,7 +1211,7 @@ tasks:
          flags: "-e ARROW_BUILD_SHARED=OFF -e ARROW_BUILD_STATIC=ON -e ARROW_TEST_LINKAGE=static"
          image: ubuntu-cpp
    
   -{% for cpp_standard in [14, 17] %}
   +{% for cpp_standard in [14, 17, 20] %}
      test-ubuntu-20.04-cpp-{{ cpp_standard }}:
        ci: github
        template: docker-tests/github.linux.yml
   ```


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