Pass a different declared type to a binding procedure Fortran

Question

Given the following code

  type t1 
     integer :: dum 
  type(aop), alloctable  :: bc(:) 
  end type t1 

 type aop 
   procedure(A_INT), pass(t1), pointer :: ptr => null()
 end type aop 

 abstract interface 
    subroutine A_INT ( this ) 
            import t1
            class(t1) , intent(in) :: this 
    end subroutine 

 end interface 

Can someone explain why this is illegal? At least the compiler says

error #8170: The passed-object dummy argument is missing from the procedure interface.   [A_INT]
            procedure(A_INT), pass(t1),
   -------------------^

UPDATED

When I do this instead

  type t1 
     integer :: dum 
  type(aop), alloctable  :: bc(:) 
  end type t1 

 type aop 
   procedure(A_INT), pass(this), pointer :: ptr => null()
 end type aop 

 abstract interface 
    subroutine A_INT ( this ) 
            import t1
            class(t1) , intent(in) :: this 
    end subroutine 

 end interface 

I get following error

error #8262: For a type-bound procedure that has the PASS binding attribute, the first dummy argument must have the same declared type as the type being defined.   [THIS]
             subroutine A_INT(  this

which I guess this means that the compiler expects the first argument to be of aop type? Is it not possible to have this being of t1 type?

Answer 1

You are using pass(t1) bu there is no dummy argument t1, there is only the argument this which is of type t1.

With a single dummy argument I would typically not use any explicit pass here at all. A passed dummy argument makes sense only when it is of the same type as the type in which the pointer is defined. Otherwise, for arguments of other types, just use nopass.