Compiler error in `type_conversion.hpp`

[eschnett]

I am using libcxxwrap-julia 0.9.7.

I encounter this error:

In file included from /usr/local/include/jlcxx/array.hpp:4:
/usr/local/include/jlcxx/type_conversion.hpp:646:100: error: cannot initialize a member subobject of type 'const void *' with an lvalue of type 'std::vector<openPMD::Datatype> (*)()'
  struct boxed_void_ptr { const void* ptr; } *presult = (struct boxed_void_ptr*)result, vresult = {cpp_ptr};
                                                                                                   ^~~~~~~
/usr/local/include/jlcxx/type_conversion.hpp:823:13: note: in instantiation of function template specialization 'jlcxx::boxed_cpp_pointer<std::vector<openPMD::Datatype> ()>' requested here
    return {boxed_cpp_pointer(&cppval, julia_type<CppT&>(), false).value};
            ^
/usr/local/include/jlcxx/type_conversion.hpp:838:10: note: in instantiation of member function 'jlcxx::BoxValue<std::vector<openPMD::Datatype> (&)(), jlcxx::WrappedCppPtr>::operator()' requested here
  return BoxValue<CppT, static_julia_type<CppT>>()(std::forward<ArgT>(cppval));
         ^
/Users/runner/work/openPMD-api/openPMD-api/src/binding/julia/Datatype.cpp:31:9: note: in instantiation of function template specialization 'jlcxx::Module::set_const<std::vector<openPMD::Datatype> (&)()>' requested here
    mod.set_const("openPMD_datatypes", openPMD_Datatypes);
        ^
1 error generated.

See here for the Github CI run that reports this error.

The compilers used are

-- The C compiler identification is AppleClang 14.0.0.14000029
-- The CXX compiler identification is AppleClang 14.0.0.14000029
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Applications/Xcode_14.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Applications/Xcode_14.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found Julia executable: /usr/local/bin/julia
-- Julia_VERSION_STRING: 1.9.2
-- Julia_INCLUDE_DIRS:   /Applications/Julia-1.9.app/Contents/Resources/julia/include/julia
-- Julia_LIBRARY_DIR:    /Applications/Julia-1.9.app/Contents/Resources/julia/lib
-- Julia_LIBRARY:        /Applications/Julia-1.9.app/Contents/Resources/julia/lib/libjulia.1.9.dylib
-- JULIA_HOME:           /Applications/Julia-1.9.app/Contents/Resources/julia/bin
-- Julia_LLVM_VERSION:   v14.0.6
-- Julia_WORD_SIZE:      64
-- Found Julia: /Applications/Julia-1.9.app/Contents/Resources/julia/lib/libjulia.1.9.dylib (found version "1.9.2") 
-- JlCxx version: v0.9.7
-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY - Success
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY - Success
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR - Success

Would an explicit cast to const void * solve the problem?

The same code compilers without errors on other (i.e. Linux) architectures.

[barche]

Unfortunately, it is not possible to set a std::vector as a module constant, since it is mapped to a pointer to that vector and this changes on every invocation. I would recommend using a lambda expression to make a function that returns the vector instead. I'll adapt libcxxwrap so that this type of use always gives a compile error.