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Subject: [Bug fortran/41951] [OOP] Not diagnosing ambiguous operators (TB vs. INTERFACE)
Date: Fri, 16 Nov 2012 12:33:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41951

--- Comment #17 from janus at gcc dot gnu.org 2012-11-16 12:33:00 UTC ---
(In reply to comment #16)
> One way to reject the abstract case in comment 11, would be to just do the
> checking, but not add the procedure to the operator list:

The only problem with the patch in comment 16 is that the error message it
gives on comment 11 ...

generic :: assignment(=) => assign
                               1
Error: Entity 'assign_it' at (1) is already present in the interface

... is technically not correct. 'assign_it' is not added twice, but in one case
is just the interface of the deferred type-boud procedure 'assign'. Instead, it
might be better to complain about 'Ambiguous interfaces' (since any
non-abstract extension of the type 'sort_t' will have to override/implement the
type-bound 'assign' with a procedure which is ambiguous to 'assign_it').

However, such an error about 'Ambiguous interfaces' is also missing for the
following case (which is still accepted):

module m_sort
  implicit none

  type, abstract :: sort_t
  contains
    generic :: assignment(=) => assign
    procedure(assign_ifc), deferred :: assign 
  end type

  abstract interface
    subroutine assign_ifc (lhs, rhs)
      import
      class(sort_t), intent(out) :: lhs
      class(sort_t), intent(in) :: rhs
    end subroutine
  end interface

  interface assignment(=)
    subroutine assign_it (lhs, rhs)
      import
      class(sort_t), intent(out) :: lhs
      class(sort_t), intent(in) :: rhs
    end subroutine
  end interface

end module