Simple way to call a Julia function throught LibraryLink

JuliaConnect.cpp

#include "WolframLibrary.h"
#include "julia.h"

DLLEXPORT mint WolframLibrary_getVersion() {
    return WolframLibraryVersion;
}

DLLEXPORT int WolframLibrary_initialize(WolframLibraryData libData) {
    return 0;
}

DLLEXPORT void WolframLibrary_uninitialize(WolframLibraryData libData) {}

EXTERN_C DLLEXPORT int juliaInit(WolframLibraryData libData, mint argc, MArgument *args, MArgument res) {
    jl_init();
    return LIBRARY_NO_ERROR;
}

EXTERN_C DLLEXPORT int juliaExit(WolframLibraryData libData, mint argc, MArgument *args, MArgument res) {
    int ret = 0;
    jl_atexit_hook(ret);
    return ret;
}



EXTERN_C DLLEXPORT int juliaFunc(WolframLibraryData libData, mint argc, MArgument *args, MArgument res) {

    mreal in = MArgument_getReal(args[0]);

    jl_eval_string("my_func(x) = 2*x");

    jl_function_t *func = jl_get_function(jl_current_module, "my_func");
    jl_value_t* arg = jl_box_float64(in);

    double ret = jl_unbox_float64(jl_call1(func, arg));

    MArgument_setReal(res, ret);
    return LIBRARY_NO_ERROR;
}