Pass by reference of map typed struct(CxxWrap.jl)

pass by reference of map typed struct(CxxWrap.jl)

Hi,

I’m trying to pass the argument by reference from Julia to C++. This argument is simple struct,
so I used map_type at wrap module difinition.

I am having trouble observing the values of arguments on the Julia side that have been changed on the c++ side.

The following is a minimal example.

What is wrong with it?


c++

struct StructTest{
    int a;
};

JLCXX_MODULE define_module(jlcxx::Module& mod)
{
    mod.map_type<StructTest>("StructTest");

    mod.method("increment", [](StructTest& s){
        s.a += 10;
        std::cout << "increment : s.a = " << s.a << std::endl;
        return s;       // The object is copied and returned for testing purposes.
    });
}

julia

module CxxTest
    struct StructTest
        a::Int32
    end

    @wrapmodule(lib_path, :define_module)

    function __init__()
        @initcxx
    end
end

Execution Result

julia> using CxxTest

julia> s = CxxTest.StructTest(10)
CxxTest.StructTest(10)

julia> CxxTest.increment(s)
increment : s.a = 20            # works correctly in the c++ side
CxxTest.StructTest(20)          # The return value is also correct.

julia> s.a                      # The value have not changed.
10