step-70: warning: possibly dangling reference to a temporary [-Wdangling-reference]

[marcfehling]

I built the library with the component examples recently with gcc 13.1.1 and I got the following warning for step-70:

Building CXX object examples/CMakeFiles/example_step_70_debug.dir/step-70/step-70.cc.o
dealii/examples/step-70/step-70.cc: In instantiation of ‘void Step70::StokesImmersedProblem<dim, spacedim>::assemble_nitsche_restriction() [with int dim = 2; int spacedim = 3]’:
dealii/examples/step-70/step-70.cc:1869:9:   required from ‘void Step70::StokesImmersedProblem<dim, spacedim>::run() [with int dim = 2; int spacedim = 3]’
dealii/examples/step-70/step-70.cc:1938:22:   required from here
dealii/examples/step-70/step-70.cc:1484:25: warning: possibly dangling reference to a temporary [-Wdangling-reference]
 1484 |             const auto &JxW    = p.get_properties()[0];
      |                         ^~~
dealii/examples/step-70/step-70.cc:1484:52: note: the temporary was destroyed at the end of the full expression ‘(& p)->dealii::Particles::ParticleAccessor<3, 3>::get_properties().dealii::ArrayView<const double>::operator[](0)’
 1484 |             const auto &JxW    = p.get_properties()[0];
      |                                  ~~~~~~~~~~~~~~~~~~^
dealii/examples/step-70/step-70.cc: In instantiation of ‘void Step70::StokesImmersedProblem<dim, spacedim>::assemble_nitsche_restriction() [with int dim = 3; int spacedim = 3]’:
dealii/examples/step-70/step-70.cc:1869:9:   required from ‘void Step70::StokesImmersedProblem<dim, spacedim>::run() [with int dim = 3; int spacedim = 3]’
dealii/examples/step-70/step-70.cc:1946:22:   required from here
dealii/examples/step-70/step-70.cc:1484:25: warning: possibly dangling reference to a temporary [-Wdangling-reference]
 1484 |             const auto &JxW    = p.get_properties()[0];
      |                         ^~~
dealii/examples/step-70/step-70.cc:1484:52: note: the temporary was destroyed at the end of the full expression ‘(& p)->dealii::Particles::ParticleAccessor<3, 3>::get_properties().dealii::ArrayView<const double>::operator[](0)’
 1484 |             const auto &JxW    = p.get_properties()[0];
      |                                  ~~~~~~~~~~~~~~~~~~^
dealii/examples/step-70/step-70.cc: In instantiation of ‘void Step70::StokesImmersedProblem<dim, spacedim>::assemble_nitsche_restriction() [with int dim = 2; int spacedim = 2]’:
dealii/examples/step-70/step-70.cc:1869:9:   required from ‘void Step70::StokesImmersedProblem<dim, spacedim>::run() [with int dim = 2; int spacedim = 2]’
dealii/examples/step-70/step-70.cc:1954:22:   required from here
dealii/examples/step-70/step-70.cc:1484:25: warning: possibly dangling reference to a temporary [-Wdangling-reference]
 1484 |             const auto &JxW    = p.get_properties()[0];
      |                         ^~~
dealii/examples/step-70/step-70.cc:1484:52: note: the temporary was destroyed at the end of the full expression ‘(& p)->dealii::Particles::ParticleAccessor<2, 2>::get_properties().dealii::ArrayView<const double>::operator[](0)’
 1484 |             const auto &JxW    = p.get_properties()[0];
      |                                  ~~~~~~~~~~~~~~~~~~^

[bangerth]

Yes, good catch. I have a patch.