Use typedef from header file that isn't #included as a return type

Question

Related to my previous question .

I need to use a typedef from a header file ( original.h ) as a return type in another header which doesn't have access to original.h . To complicate things further, this typedef is nested inside a class. I've tried directly copypasting the typedef, but the return types don't match in the cpp file (which does have access to original.h ).

Is there a way to either cast between identical typedefs or forward-declare a typedef (from searching up online the second one seems impossible, but maybe something could work considering it will only be used as a return type)?

Edit: full typedef:

typedef union
{
    struct
    {
        #ifdef __vxworks
        unsigned Comm : 8;
        unsigned Mode : 8;
        unsigned RSL : 1;
        #else
        unsigned RSL : 1;
        unsigned Mode : 8;
        unsigned Comm : 8;
        #endif
    };
    struct
    {
        unsigned value : 17;
    };
} tLEDs;

Answer 1

I ended up just manually writing a function to copy all fields of the struct, ie for this problem:

LEDs tleds_to_leds(tLEDs tleds)
{
    LEDs leds;
    leds.rsl = tleds.RSL;
    leds.mode = tleds.Mode;
    leds.comm = tleds.Comm;
    leds.value = tleds.value;
    return leds;
}