group_name_list Function

   function group_name_list(this) result(names)
      !! All registered + external group names as a char array.
      type(nml_schema_t), intent(in) :: this
      character(len=:), allocatable :: names(:)
      integer :: ng, ne, i, mlen, k

      ng = 0
      if (allocated(this%groups)) ng = size(this%groups)
      ne = 0
      if (allocated(this%external_names)) ne = size(this%external_names)
      mlen = 1
      do i = 1, ng
         mlen = max(mlen, len(this%groups(i)%name))
      end do
      if (ne > 0) mlen = max(mlen, len(this%external_names))
      allocate (character(len=mlen) :: names(ng + ne))
      k = 0
      do i = 1, ng
         k = k + 1
         names(k) = this%groups(i)%name
      end do
      do i = 1, ne
         k = k + 1
         names(k) = this%external_names(i)
      end do
   end function group_name_list