virtual instance variables

virtual instance variables

[Jeremy Yallop]

Should this be considered a bug?

    # (object val virtual c : float method m = c end) # m;;
    Segmentation fault

Re: [Caml-list] virtual instance variables

[Jon Harrop]

On Thursday 28 June 2007 14:34:20 Jeremy Yallop wrote:
> Should this be considered a bug?
>
>     # (object val virtual c : float method m = c end) # m;;
>     Segmentation fault

Yes:

$ ocaml
        Objective Caml version 3.09.1

# (object val virtual c : float method m = c end) # m;;
Syntax error

$ ocaml
        Objective Caml version 3.10.0

# (object val virtual c : float method m = c end) # m;;
Signal -10

and what is signal -10?! :-)

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
The OCaml Journal
http://www.ffconsultancy.com/products/ocaml_journal/?e

Re: [Caml-list] virtual instance variables

[Vincent Hanquez]

On Thu, Jun 28, 2007 at 02:47:59PM +0100, Jon Harrop wrote:
> $ ocaml
>         Objective Caml version 3.10.0
> 
> # (object val virtual c : float method m = c end) # m;;
> Signal -10
> 
> and what is signal -10?! :-)

$ ocaml
        Objective Caml version 3.10.0

# Sys.sigsegv;;
- : int = -10
# 


-- 
Vincent Hanquez

Re: [Caml-list] virtual instance variables

[Jacques Garrigue]

From: Jeremy Yallop <jeremy.yallop@ed.ac.uk>

> Should this be considered a bug?
> 
>     # (object val virtual c : float method m = c end) # m;;
>     Segmentation fault

Any segmentation fault using no unsafe features is clearly a bug, and
should go in the bug database.
Should be fixed soon.

Jacques Garrigue

Re: [Caml-list] virtual instance variables

[Jacques Garrigue]

From: micha <micha-1@fantasymail.de>

> entering in the toplevel: 
> 
> class virtual c = object val virtual d : int end;;
> 
> then:
> 
> class d = object inherit c val d = 9 end;;
> 
> gives me: Exception: Not_found.
> What is not found?  (compiling works)

Great, you found the first bug in this release!
To trigger it you must create a virtual instance variable without
using it (which is certainly useless, but allowed.)
This is now fixed in CVS.

Note that if you write 
  class virtual c = object val virtual d : int method d = d end;;
there is of course no problem.

> if I define:
>  class virtual c = object val d = 0 end;;
>  class d = object inherit c val d = 9 end;;
> 
> gives the warning:
> Warning V: the instance variable d is overriden.
> The behaviour changed in ocaml 3.10 (previous behaviour was hiding.)
> 
> I thought that  without the virtual declaration the behaviour is the
> same as before?

No, it is not. Or, more precisely, we reverted to the behviour of
ocaml 1. Visible instance variables are merged. To avoid this, you
must hide the first d by a coercion:

class d = object inherit (c : object end) val d = 9 end;;

Jacques Garrigue