ensure_authoring_particle_capacity Subroutine

  subroutine ensure_authoring_particle_capacity(authoring, required_size)
    type(app_config_authoring), intent(inout) :: authoring
    integer, intent(in) :: required_size
    type(particle_authoring_spec), allocatable :: grown(:)
    integer :: old_capacity, new_capacity

    if (required_size <= 0) return
    if (allocated(authoring%particle_species)) then
      old_capacity = size(authoring%particle_species)
    else
      old_capacity = 0
    end if
    if (old_capacity >= required_size) return

    new_capacity = max(required_size, max(1, 2*old_capacity))
    allocate (grown(new_capacity))
    grown = particle_authoring_spec()
    if (old_capacity > 0) grown(1:old_capacity) = authoring%particle_species(1:old_capacity)
    call move_alloc(grown, authoring%particle_species)
  end subroutine ensure_authoring_particle_capacity