single_map_add Subroutine

  subroutine single_map_add(map, ptr)
    !! Add pointer to single-array map (grow if needed)
    implicit none
    type(array_ptr), allocatable :: map(:)
    type(array_type), intent(in), target :: ptr
    integer :: n, i

    if(.not. allocated(map))then
       allocate(map(diffstruc__init_map_cap))
    end if
    n = size(map)
    ! find first null slot
    do i = 1, n
       if(.not. associated(map(i)%p))then
          map(i)%p => ptr
          return
       end if
    end do
    ! no slot -> grow (double capacity)
    block
      type(array_ptr) :: tmp(n)
      integer :: newcap
      newcap = n
      tmp = map
      deallocate(map)
      allocate(map(n + newcap))
      map(1:n) = tmp
    end block
    map(n+1)%p => ptr
  end subroutine single_map_add