Support for the Ruby 2.4 series has ended. See here for reference.
See also BigDecimal.new
 
               static VALUE
BigDecimal_global_new(int argc, VALUE *argv, VALUE self)
{
    ENTER(1);
    Real *pv;
    VALUE obj;
    obj = TypedData_Wrap_Struct(rb_cBigDecimal, &BigDecimal_data_type, 0);
    GUARD_OBJ(pv, BigDecimal_new(argc, argv));
    if (ToValue(pv)) pv = VpCopy(NULL, pv);
    RTYPEDDATA_DATA(obj) = pv;
    return pv->obj = obj;
}