Overloading Present for multiple arguments

Question

Is it possible to overload Present(arg) so I can have Present(arg1,arg2,...) to mean

If (Present (arg1) .And. Present (arg2) .And. ... )

I am trying to do it but it feels as though it is not so straightforward to do.

Answer 1

Interestingly the answer is: no, you cannot. You can indeed create a generic identifier called present and have a new specific name:

module mod
  interface present
    module procedure present_two_real
  end interface
contains
  logical function present_real_real(a,b)
    ..
  end function
end module

However, inside that function we know that the dummy arguments must be optional. If they weren't it wouldn't be legal to pass optional actual arguments in a procedure to that function: see Fortran 2008 12.5.2.12.

When we look at how we different two procedures must be to be able to have the same generic identifier (12.4.3.4.5) we have constraint C1215. It's this constraint with the optional requirement in the new specific name which makes us unable to do what you want. Note that the argument in the specific procedure present isn't optional.

That doesn't mean you can't have a generic present_all, of course. You'll need a specific procedure for each combination of argument characteristics you want, though (as my choice of specific name above suggests). [Recall that template's are not in Fortran's style.] Further, you'll still need to handle the requirement to distinguish the specific implementations. It all sounds like a bit too much work, really.