Functions takes arrays and outputting another array

[uzibalqa]

I want to make a bash function that takes two arrays and outputs another array.

Here I use "typeset".  Should I use "declare" instead as in (declare -n 
_array1="$1" _array2="$2") ?

For the output, I have thought about introducing a null.  Is this the correct 
way to output arrays
from a function?

fill_array()
  typeset -n _array1="$1" _array2="$2"
  typeset _ext
  for _ext in "${_array1[@]}"; do
    case $_ext in
      (PEXTD) _out+=( '--include=*.'{cp,cpp,f90,f95,f03,f08} ) ;;
      (PROGL) _out+=( '--include=*.'{rc,el,c,f} ) ;;
      (TYPOG) _out+=( '--include=*.'{org,texi,tex} ) ;;
      (*) continue
    esac
    printf '%s\0" "${_out[@]}"
  done
}