Errors With Declarations

[TLWise]

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Question

I am using the following code:
'''InputParameters
IntegralDirectedSurfaceForceFEM::validParams()
{
InputParameters params = SideIntegralPostprocessor::validParams();
params.addClassDescription("Computes the directed force from friction and pressure differences on a surface.");
params.addRequiredParam("vel_x", "The velocity in the x-direction.");

: SideIntegralPostprocessor(parameters),
_vel_x(getFunctor("vel_x")),'''

I am getting the following error:
'''/home/twise/projects/crab/src/postprocessors/IntegralDirectedSurfaceForceFEM.C:36:28: error: invalid initialization of reference of type 'const VariableValue&' {aka 'const MooseArray&'} from expression of type 'Moose::Functor' {aka 'const Moose::FunctorEnvelope'}
36 | _vel_x(getFunctor("vel_x")), // _vel_x(getFunctor("vel_x")),
| ~~~~~~~~~~~~~~~~^~~~~~~~~'''

[TLWise]

Adding Templ<is_ad> appears to have eliminated the problem.

[GiudGiud]

the error here

invalid initialization of reference of type 'const VariableValue&' {aka 'const MooseArray&'} from expression of type 'Moose::Functor'

says that you have _vel_x as a variable value, which you can initialize with coupledValue from the Coupleable interface.
But you are trying to initialize it with getFunctor, which is meant for retrieving references to functors