[Bug fortran/45516] New: [F08] allocatable compontents of recursive type

[Bug fortran/45516] New: [F08] allocatable compontents of recursive type

[janus at gcc dot gnu dot org]

John Reid, The new features of Fortran 2008, chapter 5.3:

A recursive type is permitted to be based on allocatable components. Here is a
simple example of a type that holds a stack:

type entry
  real :: value
  integer :: index
  type(entry), allocatable :: next
end type entry

[...]

For this gfortran currently gives:

  type(entry), allocatable :: next
                                  1
Error: Component at (1) must have the POINTER attribute


-- 
           Summary: [F08] allocatable compontents of recursive type
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: janus at gcc dot gnu dot org
OtherBugsDependingO 39627
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45516

[Bug fortran/45516] [F08] allocatable compontents of recursive type

[janus at gcc dot gnu dot org]

------- Comment #1 from janus at gcc dot gnu dot org  2010-09-03 09:59 -------
Here is a patch to accept the type declaration in comment #0:

Index: decl.c
===================================================================
--- decl.c      (revision 163798)
+++ decl.c      (working copy)
@@ -1494,11 +1494,11 @@ build_struct (const char *name, gfc_charlen *cl, g
   gfc_component *c;
   gfc_try t = SUCCESS;

-  /* F03:C438/C439. If the current symbol is of the same derived type that
we're
-     constructing, it must have the pointer attribute.  */
+  /* F08:C440. If the current symbol is of the same derived type that we're
+     constructing, it must be POINTER or ALLOCATABLE.  */
   if ((current_ts.type == BT_DERIVED || current_ts.type == BT_CLASS)
       && current_ts.u.derived == gfc_current_block ()
-      && current_attr.pointer == 0)
+      && !current_attr.pointer && !current_attr.allocatable)
     {
       gfc_error ("Component at %C must have the POINTER attribute");
       return FAILURE;


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45516

[Bug fortran/45516] [F08] allocatable compontents of recursive type

[burnus at gcc dot gnu dot org]

------- Comment #2 from burnus at gcc dot gnu dot org  2010-09-03 12:12 -------
(In reply to comment #1)
> Here is a patch to accept the type declaration in comment #0:

Well, you at least need to use gfc_notify_std(GFC_STD_F2008, ... And one should
make sure that the allocation/clean up works as expected.

 * * *

As follow up to the initial implementation, one should implement at some point
the following, which does not do a deep copy but simply appends the old data.
(Example from the mentioned article.)

type entry
  real :: value
  integer :: index
  type(entry), allocatable :: next
end type entry

type (entry), allocatable :: top
top = entry ( new_value, new_index, top )

(The last line assume reallocate on assignment; I think it already works for
derived types with structure constructor; I know that it does not yet work for
intrinsic types - not does it work on other assignment than structure
constructors.)

The classical way to append a new item is the following, which should avoid a
deep copy (check!):

  type (entry), allocatable :: top, temp
  temp = entry ( new_value, new_index, temp )
  call move_alloc(top,temp%next)
  call move_alloc(temp,top)


-- 

burnus at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |domob at gcc dot gnu dot
                   |                            |org, burnus at gcc dot gnu
                   |                            |dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45516