Thoughts on allocatable components

[Erik Edelmann]

Here's some thoughts about implementing the allocatable
components stuff.  Fell free to add things to the list if I
forgot something (or remove things, if you feel they shouldn't be
there :-).

What needs to be done (roughly in this order):

* Declaration of allocatable components, explicit allocation &
  deallocation.  NOTE: Deallocation recursive if necessary.

* Automatic deallocation:

    * Automatic variables on procedure exit.
    * Function results, when the result has been used
    * INTENT(OUT) dummies on procedure entry.

* Assignments: Allocate automatically, if not allocated to the
  correct size (deallocate first if allocated to the wrong size)

* In a structure constructor for such a type, the expression
  corresponding to an allocatable array component can be

    * The NULL() intrinsic, indicating an unallocated array.
    * An allocatable array which may be allocated or unallocated.
    * Any other array expression, indicating an allocated array.


Difficulties:

* The recursive deallocations might be a bit tricky.  When that's
  working, the automatic deallocation things will be pretty
  straight forward.

* The assignment-stuff is going to be hard as well.  It depends a
  little bit on how optimal we want to make it of course:  the
  "simple" but sub-optimal solution would be to allways
  deallocate (and then allocate again).

* I'm not yet sure how hard the structure constructor part will
  be.


        Erik