J3/05-127r1

Date:    8 February 2005
To:      J3
From:    Van Snyder
Subject: Implicit interfaces and conflicting references

NUMBER:

TITLE: Implicit interfaces and conflicting references

KEYWORDS: implicit interface, procedure pointer, dummy procedure,
          procedure reference

DEFECT TYPE:

STATUS: J3 consideration in progress

QUESTION:
Is the following program legal:

_________________________
module test_mod

contains

subroutine reference(proc,choice)
    ! Proc has implicit interface
    external :: proc ! Or
        ! procedure(), pointer :: proc
    logical :: choice
    if(choice) then
       call proc(1.0) ! Call with real argument
    else
       call proc(1) ! Call with integer argument
    end if
end subroutine

subroutine proc_real(x)
   real :: x
end subroutine

subroutine proc_integer(x)
   integer :: x
end subroutine

end module

program test
   use test_mod
   call reference(proc_real,.true.)
   call reference(proc_integer,.false.)
end program
_________________________

12.3.2.5 says: "The type...of dummy arguments of a procedure referenced
from a scoping unit  where the interface of  the procedure is implicit
shall be such that the actual arguments  are consistent with the
characteristics of the dummy arguments." We define a procedure reference
in 2.5.6 as the "appearance of  procedure designator, ... in a context
requiring execution at that point."

Are both calls to proc above references, at compile time? If both calls
to proc are references then they both need to be consistent with the
interface of the actual argument associated with the dummy procedure.
This is not possible and the program would be illegal. However, if only
the call executed counts as a reference, than the program is legal.

The same question applies to both dummy procedures and procedure pointers
with implicit interfaces.

ANSWER:

The program is not standard conforming.  Both calls to PROC in the module
subroutine REFERENCE are references to the dummy procedure PROC and must
be consistent.

Consider the definitions of <<procedure reference>> and <<data object
reference>> in 2.5.6.  The terminology in both cases is "the appearance
of the [entity] in a context requiring its... at that point."

There is no controversy that, for example, a program containing an
intrinsic assignment statement wherein <variable> and <expr> have
different declared derived types is not standard conforming, even if the
statement is never executed.

EDITS:

None.

SUBMITTED BY: Aleksandar Donev

HISTORY: J3/05-127   m171 Submitted