[J3] Same specific procedure for multiple type-bound procedures?

[Malcolm Cohen]

Hi Daniel,

 

Without looking at the code, of course the same *actual* procedure could be
used to implement more than one type-bound procedure.

 

Do not use the word specific here: specific has a technical meaning, and you
will just confuse yourself. Asking whether the same *specific* procedure can
be used for more than one type-bound procedure is *meaningless*. Type-bound
procedures are themselves *specific* (unless they are generic, of course,
just like procedure names are specific unless they are generic).

 

One binds an *actual* (or "ordinary" if you prefer) procedure to be the
implementation of a *specific* type-bound procedure. The type-bound
procedure is not the actual procedure, the actual procedure is merely the
implementation *in that type*.

 

A generic named procedure is a set of *specific* ordinary procedures that
satisfy the ambiguity rules.

 

A generic type-bound procedure is a set of *specific* type-bound procedures
that satisfy the ambiguity rules.

 

It is all very simple and consistent: "named generic: set of named
procedures" and "type-bound generic: set of type-bound procedures". In the
type-bound procedure case, it does not matter what the implementing
procedures are, it is the type-bound procedures that must satisfy the
generic rules. That is because the type-bound procedures can be overridden
individually, so generic resolution absolutely needs non-ambiguous
resolution: whether one of the types uses the same actual procedure to
implement two type-bound procedures is simply irrelevant and unhelpful to
consider.

 

When the generic type-bound procedure is an operator, the resulting generic
set will consist of all procedures, type-bound or otherwise, with that
operator symbol in a scope. The ambiguity rules in 15.4.3.4.5 work equally
on pairs of named procedures, pairs of type-bound procedures, and pairs
consisting of one named procedure and one type-bound procedure.

 

BOTH of your examples are invalid because the specific type-bound procedures
do NOT satisfy the ambiguity rules:

 

Error: chen1.f90, line 24: Ambiguous specific type-bound procedures G and F
for type-bound generic OPERATOR(+) in type BASE1

 

Error: chen2.f90, line 18: Ambiguous specific type-bound procedures BASE2
and BASE1 for type-bound generic OPERATOR(+) in type BASE

 

Cheers,

-- 

..............Malcolm Cohen, NAG Oxford/Tokyo.

 

From: J3 <j3-bounces at mailman.j3-fortran.org> On Behalf Of Daniel Chen via J3
Sent: Wednesday, January 29, 2025 6:04 AM
To: Van Snyder via J3 <j3 at mailman.j3-fortran.org>
Cc: Daniel Chen <cdchen at ca.ibm.com>
Subject: [J3] Same specific procedure for multiple type-bound procedures?

 

Hello,
As in the following code,

Case 1:
```
module m

 

   type base

      integer :: i = -999

      contains

         procedure, pass(b) :: g => int_base1_base    !! Same specific

         generic :: operator(+) => g

   end type

 

   type base1

      integer :: j  = -999

      contains

         procedure, pass :: f => int_base1_base       !! Same specific

         generic :: operator(+) => f

   end type

 

   contains

 

   integer function int_base1_base ( a, b )

      class(base1), intent(in) :: a

      class(base), intent(in) :: b

   end function

 

end module


```

Case 2:
```
module m
 
   type base
      integer :: i = -999
      contains
         procedure, pass(b) :: base1 => base_base_base   !! Same specific
         procedure, pass(b) :: base2 => base_base_base   !! Same specific
         generic :: operator(+) => base1, base2
   end type
 
   contains
 
   type(base) function base_base_base ( a, b )
      class(base), intent(in) :: a
      class(base), intent(in) :: b
   end function
 
end module


```

Are these 2 cases legal?  Can multiple binding-name from either different
types or the same type point to the same specific procedure?
I didn't find any wording in the standard that disallows it.

Thanks,
Daniel



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