Can I use decltype?

[長田偉伸]

[Description]
  Please confirm the attached file

[Cause location]
  $base = std::static_pointer_cast<decltype($base)::element_type>($sub);

[Error Message]
  $ bison parser.yy; clang++-6.0 -std=c++17 -Wall -Wextra -g -O0 parser.cc
  parser.yy:87:79: error:
'decltype(yylhs.value.as<std::shared_ptr<Baseclass> >())' (aka
'std::shared_ptr<Baseclass> &')
        is not a class, namespace, or enumeration
                          yylhs.value.as< std::shared_ptr<Baseclass> >
() = std::static_pointer_cast<decltype(yylh...

                              ^
  1 error generated.

[Environment]
  OS: Windows10 (WSL)
  Bison: version 3.1.91
  clang: version 6.0.0

parser.yy
Description: Binary data