new_contents: from dune.xt.grid import Dim, Cube, make_cube_grid
  
  grid = make_cube_grid(Dim(1), [0], [1], [2])
  d = grid.dimension
  
  from dune.xt.functions import ConstantFunction, GridFunction
  from dune.xt.la import Istl
  from dune.gdt import ContinuousLagrangeSpace, MatrixOperator, LocalElementIntegralBilinearForm, LocalLaplaceIntegrand
  
  space = ContinuousLagrangeSpace(grid, 1)
  op = MatrixOperator(grid, space, space, Istl())
  
  func = ConstantFunction(Dim(1), Dim(1), [1])
  op += LocalElementIntegralBilinearForm(LocalLaplaceIntegrand(GridFunction(grid, func, (Dim(d), Dim(d)))))
  del func
  op.assemble()
  
  
subject: document problematic data function lifetime