Re: [Patch,Fortran] Add polymorphic type support (OOP, RTTI) - merge from Fortran-dev branch

[Daniel Kraft <d at domob dot eu>]

Hi Paul,

Paul Richard Thomas wrote:
> Dear All,
>
> Please find attached the patch for dynamic dispatch that Tobias
> referred to.  It is incomplete, in that subroutines do not yet work
> and the testcases have not yet been supplied.  However, it does handle
> both specific and generic functions correctly.

here are some comments regarding your patch:

Your dynamic dispatch is done (if I understood it correctly) by building 
a switch on the vindex which has labels for each subtype of the CLASS' 
declared type and where the then-appropriate procedure is called.  Am I 
right here?

I'm not sure about what we would expect in that case, but from a C++ 
point of view, one should be allowed to declare a derived-type in a 
module and use it there with CLASS, but the compiled code should also 
work when passed a CLASS object whose actual type is some subtype that 
was unknown at compile-time of the original module.  Would this work?

Tobias mentioned a possible rework of the internal structure for 4.6, so 
I guess this is not something really important...  But later on, we 
could instead use a vtable of procedure-pointers for dynamic dispatch; 
IIRC, you even mentioned one some time, didn't you?  Just some thoughts, 
though.

+      /* If we have to match a passed class member, force the actual
+	 expression to have the correct type.  */
+      if (!tbp->n.tb->nopass)
+	{
+	  if (e->value.compcall.base_object == NULL)
+	    {
+	      e->value.compcall.base_object = gfc_get_expr ();
+	      e->value.compcall.base_object->expr_type = EXPR_VARIABLE;
+	      e->value.compcall.base_object->symtree = e->symtree;
+	      e->value.compcall.base_object->ref = gfc_copy_ref (e->ref);
+	    }

You could replace those four lines generating the base_object by a call 
to extract_compcall_passed_object if you want, but of course you don't 
save much.  I'd still do it, I guess.

All in all, I think the patch is ok.  But as I've not yet really read 
the other polymorphism patch, I don't feel confident to give a review 
here (and you didn't yet request one, did you?).

Thanks for your and Janus' work here!
Daniel

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