Libjulia: is it really necessary to wrap immutable variables to protect them and why?

General Usage
1

Hello here,

I have a C wrapper that calls Julia functions using libjulia and wraps the result in an IdDict, for example:

int64_t jl_setindex_wrap_eval_string(int64_t index, const char* code)
{
    if (index == 0){
        jl_printf(jl_stderr_stream(), "ERROR: index is 0 (jl_setindex_wrap_eval_string)\n");
        return(0);
    }else if (code == NULL){
        jl_printf(jl_stderr_stream(), "ERROR: empty code string (jl_setindex_wrap_eval_string)\n");
        return(0);  
    }
    jl_value_t *res = jl_eval_string(code);
    JL_CHECK_EXCEPT(0)
    JL_GC_PUSH1(&res);
    jl_call3(setind, refs, res, jl_box_int64(index));
    JL_GC_POP();
    return(index);
}

Where setind is the setindex! function.

From the documentation (Embedding Julia: Embedding Julia · The Julia Language), I knew that, immutable variables “needs to be wrapped in an equivalent mutable container or, preferably, in a RefValue{Any} before it is pushed to IdDict .”. Here refs is an IdDict.

I use this code for mutable and immutable ((scalars and (named)Tuple) values since a while so I wanted to know why it is necessary and if this is mandatory.

Some informations about this? And which bad effects can happen? I have not encountered some.

Greg