[Bug fortran/42385] [OOP] poylmorphic operators do not work

[damian at rouson dot net]

------- Comment #1 from damian at rouson dot net  2010-05-21 14:01 -------
As suggested by Janus and Paul, I'm adding the additional test case below. Note
that the first two pointer assignments in main are not necessary to demonstrate
the linking problem. I put them there (1) to give more detail about what I was
trying to do and (2) because deleting those leaves pointless code since there
would be no reason to do the the third assignment without doing the first two.

$cat link_demo.f03
module field_module
  implicit none

  type ,abstract :: field 
  contains
    procedure(field_eq_field) ,deferred :: assign         
    generic :: assignment(=) => assign
  end type

  abstract interface
    subroutine field_eq_field(lhs,rhs)
      import :: field
      class(field) ,intent(out) :: lhs
      class(field) ,intent(in) :: rhs
    end subroutine
  end interface 
end module
module periodic_field_module
  use field_module ,only : field
  implicit none

  type ,extends(field) :: periodic_field
    real :: f=0.
  contains
    procedure :: assign => copy
  end type

contains
  function new_periodic_field()
    type(periodic_field) ,pointer :: new_periodic_field
    allocate(new_periodic_field)
  end function

  subroutine copy(lhs,rhs)
    class(field) ,intent(in) :: rhs
    class(periodic_field) ,intent(out) :: lhs
    select type(rhs)
      class is (periodic_field)
        lhs%f = rhs%f
      class default
        stop 'periodic_field%copy: unsupported right-hand-side class.'
    end select
  end subroutine
end module
program main
  use field_module 
  use periodic_field_module 
  implicit none
  class(field) ,pointer :: u,f
  u => new_periodic_field() 
  f => new_periodic_field()
  f = u
end program

$ gfortran link_demo.f03 
Undefined symbols:
  "_field_eq_field_", referenced from:
      _MAIN__ in ccFO42I9.o
ld: symbol(s) not found
collect2: ld returned 1 exit status


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42385